IRRIGATION SYSTEMS AND DESIGN - IWRE 317 questions collection 1997 - 2018 (COURSE INSTRUCTOR: PROFESSOR A. K. TARIMO)

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Design of irrigation system
IWRE 317
QUESTIONS COLLECTION
TESTs AND UEs
1997 – 2018
COMPILED BY Musadoto IWRE- 3

PROBATION/FIRST SITTING UNIVERSITY EXAMINATION (SEMESTER 5)
IWRE 317
IRRIGATION SYSTEMS AND DESIGN
ACADEMIC YEAR 2009/2010
THIRD YEAR
IWRE AND AGE STUDENTS
September 2010
Q1 (a) Outline what you understand about the term pump characteristic curves and their
respective importance in pump selection (10 Marks)
(b) A sprinkler irrigation system requires a centrifugal pump to operate. It was found out
that a small centrifugal pump with a discharge of 0.046 m3
/s could pump the irrigation
water at a head of 24 m if it is operating with an efficiency of 80 %. It was also found
that at this head, it requires 17.8 kW at 1400 rpm. Assuming the efficiency of the
pump remains constant, what is the theoretical discharge of the pump if its speed is
increased to 2000 rpm? What are the theoretical head and horsepower at 2000 rpm?
(15 Marks)
Q2` a) Briefly explain the major difference between drip irrigation and other irrigation
systems. (10 Marks)
b) If the conventional peak ETc is 10 mm/day and 80% of the area is shaded by trees in
an orchard, determine the design ETc rate, volume of water required per tree per day,
and application rate in L/h per tree for a drip irrigation system. Assume EU = 0.93, a
tree spacing of 3 x 6 m, 20 h/day operation and irrigation interval of 2 days. Also,
determine the number of emitters required per tree. Assume a medium textured soil
of low density, a 1.5 m root zone and 45% of the area is to be irrigated. Hint: Make
use of Table 1. (15 Marks)
Table 1: Estimated Maximum Diameter of the Wetted Circle Formed by
Single Emission Outlet Discharging 4L/h on Various Soils

Varying Layers
________________________________
Soil or Root Homogenous Generally Low Generally Medium
Depth and Soil Density Density
Soil Texture (m) (m) (m)
Depth 0.75m
Coarse 0.45 0.75 1.05
Medium 0.90 1.2 1.5
Fine 1.05 1.5 1.8
Depth 1.5m
Coarse 0.75 1.4 1.8
Medium 1.2 2.1 2.7
Fine 1.5 2.0 2.4
Q3 (a) i) Briefly explain how to measure the consumptive use of field crops. (6 Marks)
ii) Briefly explain three different methods that are used to estimate
consumptive use of a particular crop. (6 Marks)
(b) The root zone of a certain soil has a field capacity of 180 mm and a wilting point
of 100 mm. The consumptive use of crops in July is 6 mm/day. Assuming no
rainfall, how often ought a farmer to irrigate? How much water should be applied
at each irrigation if there is to be no deep percolation? (13 Marks)
Q4 (a) Explain briefly why sprinkler system of irrigation is preferred to surface methods
of irrigation. (10 Marks)

(b) Determine the total pumping head for a sprinkler irrigation system on a level land.
The average operating pressure at the nozzle is 3kg/cm2
. The friction loss in the
main is 6.5 m and in the lateral is 4 m; the depth from the centre line of the pump
to the water level is 5 m and the required discharge is 31.6 L/s. The riser height is
1.5 m and friction loss in all valves 3.25 m. Determine the horsepower
requirements of the pump if it operates at 65 % efficiency. (15 Marks)
IWRE 317
THIRD YEAR
IWRE AND AGE STUDENTS
October 2011
systems. (10 Marks)
c) If the conventional peak ETc is 10 mm/day and 80% of the area is shaded by trees in
an orchard, determine the design ETc rate, volume of water required per tree per day,
and application rate in L/h per tree for a drip irrigation system. Assume EU = 0.93, a
tree spacing of 3 x 6 m, 20 h/day operation and irrigation interval of 2 days. Also,
determine the number of emitters required per tree. Assume a medium textured soil
of low density, a 1.5 m root zone and 45% of the area is to be irrigated. Hint: Make
use of Table 1. (15 Marks)

Varying Layers
________________________________
Depth 0.75m
Coarse 0.45 0.75 1.05
Medium 0.90 1.2 1.5
Fine 1.05 1.5 1.8
Depth 1.5m
Coarse 0.75 1.4 1.8
Medium 1.2 2.1 2.7
Fine 1.5 2.0 2.4
Q2 A soil sample with a wet weight of 300 g has 28.0 percent water content on a mass basis.
Its saturated water content is 36.1 percent on a mass basis. Assume density of water equals
1.00 g/cm3
and density of soil particles equals 2.65 g/cm3
.
(a) Find the mass of water, soil porosity, and air filled porosity of the sample at 28.0
percent water content (12 marks)
(b) If the sample at 28.0 percent water content is representative of the top 45 cm of a
0.3 ha plot, how much water, in m3
and as an average areal depth in cm, must drain
from the top 45 cm to increase the air filled porosity to 25.0 percent? (13 marks)
Q3 (a) Define the following terms:

i) Consumptive use of a crop (3 marks)
ii) Irrigation interval (3 marks)
iii) Peak irrigation water requirement (3 marks)
(b) Determine the total pumping head for a sprinkler system on level land. The average
pressure at the nozzle is 280 kPa; the friction loss in the main is 6.2 m, and in the
lateral is 3.6 m; the drawdown of the well is 4.5 m at the required discharge of 35
L/s; the riser height is 1.0 m; and friction loss in all valves is 3.2 m. Determine the
power requirements for the pump if it operates at 70 % efficiency. (16 marks)
Q4 (a) Discuss the following terms:
i) Net irrigation water requirement, (3 marks)
ii) Seasonal irrigation water requirement, (3 marks) and
iii) Readily available moisture. (3 marks)
(b) A stream of 150 litres per second was diverted from a canal and 120 litres per
second were delivered to the field. An area of 2.0 hectares was irrigated in 9 hours.
The effective depth of root zone was 2 m. The run off loss in the field was 450 m3
.
The depth of water penetration varied linearly from 2 m at the head end of the field
to 1.4 m at the tail end. Available moisture holding capacity of the soil is 220
mm/m depth of the soil. Determine the water conveyance efficiency, water
application efficiency, and water storage efficiency. Irrigation was started at
moisture extraction level of 50% of the available water.
TEST
AE 313
THIRD YEAR
AGRICULTURAL ENGINEERING STUDENTS

Time 2 hours
1.00 g/cm3
.
percent water content.
from the top 45 cm to increase the air filled porosity to 25.0 percent?
Q2 (a) Explain the difference in between a water storage efficiency and water application
efficiency.
(b) Shortly, explain how you would determine the overall efficiency of an irrigation
system.
(c) Water is applied through a cut-throat flume to a level basin system which is 0.3 ha
in area. The water is applied for 120 minutes with flow measured through the flume
at 11.8 L/s. The root zone has a capacity to store an equivalent depth of 26 mm of
water. State which efficiencies are applicable and compute their values.
Q3 (a) Explain how one would determine the operating pressure of a sprinkler system at
the junction of the main pipe and the lateral line.
(b) A lateral runs down-slope on a ground surface with constant slope of 0.010 m/m.
The actual friction loss in the lateral is 0.0085 m/m and the lateral length is 274 m.
A 1.2 m riser is required for the crop. Compute the design operating pressure for
the sprinkler nozzle if the pressure head required at the mainline is 3448 kPa.

Q4 (a) Explain factors that influences the application efficiency of a drip irrigation system.
(b) A trickle system is to be designed for an established orchard in which the field slope
is greater than 2 percent and spacing between trees is greater than 4 m. Four point
source emitters corresponding to long-path-type C in Fig. 1 are to be used per tree.
Design emitter discharge is 8.0 L/h and the manufacturer’s coefficient of variation
is 0.08. The minimum design emission uniformity is 85%.
Compute the minimum emitter discharge and corresponding minimum emitter
pressure. And why is necessary to know the minimum pressure head?
Fig 1: Discharge rates for various emitter designs as a function of operating head

TEST
AE 313
THIRD YEAR
Time 3 hours
Q1 (a) Explain the effect of change of speed and impeller diameter on pump
performance. (6marks)
(b) An existing irrigation system has a pump which delivers 3500L/min flow at a total
head of 70.0m The impeller diameter is 30.0cm and it is rotated at 1800rpm. A
motor with an output shaft power of 60 horsepower is required to drive the pump.
The existing irrigation system is modified to incorporate low pressure nozzles and
make other reductions in friction head loss. The required flow rate is unchanged but
the discharge pressure requirement is reduced to 55.0m head. It is decided to keep
the existing pump but to pull and trim the impeller to match the new system
requirements.
(i) Determine the impeller diameter required for the new discharge conditions
and the shaft horsepower necessary to drive the modified pump (9 marks).
(ii) Compute the flow rate which will have to be produced by an additional
pump to meet the original discharge requirements when the modified pump
is re-installed (10 marks).

i)Net irrigation water requirement, (3 marks)
ii)Seasonal irrigation water requirement, (3 marks) and
iii)Readily available moisture. (3 marks)
(b) A stream of 150 litres per second was diverted from a canal and 120 litres per
second were delivered to the field. An area of 2.0 hectares was irrigated in 9 hours.
The effective depth of root zone was 2 m. The run off loss in the field was 450 m3
.
The depth of water penetration varied linearly from 2 m at the head end of the field
to 1.4 m at the tail end. Available moisture holding capacity of the soil is 220
mm/m depth of the soil. Determine the water conveyance efficiency, water
application efficiency, water storage efficiency and water distribution efficiency,
if irrigation was started at a moisture extraction level of 60 % of the available
moisture (16 marks)
Q3 (a) Define the following terms:
a) Consumptive use of a crop (3 marks)
b) Irrigation interval (3 marks)
c) Peak irrigation water requirement (3 marks)
(b) Determine the total pumping head for a sprinkler system on level land. The
average pressure at the nozzle is 280 kPa; the friction loss in the main is 6.2 m, and
in the lateral is 3.6 m; the drawdown of the well is 4.5 m at the required discharge
of 35 L/s; the riser height is 1.0 m; and friction loss in all valves is 3.2 m. Determine
the power requirements for the pump if it operates at 70 % efficiency. (16 marks)
Q4 (a) Define the term emission uniformity of a drip irrigation system (10 marks)
(b) Determine the emission uniformity for a large long-path emitters if the
manufacturer’s coefficient of variation is 0.15. The are four emitters per plant,
average operating pressure is 90 kPa, and minimum pressure is 80 kPa.. Hint: make
use of Fig 1. (15 marks)

Fig 1: Discharge of various emitters versus pressure head. Values of K and x are for pressure in
kPa and flow in L/h

TEST
AE 313
THIRD YEAR
Date: 31st January 2012
1. A 10 ha cropped field (peak crop evapotranspiration is 5 mm/day and rooting depth of
0.915 m) has been irrigated by a hand moved portable sprinkler irrigation system. The soil
in this field is loam with field capacity soil moisture content (θfc) of 21% by volume and
wilting point water content (θwp)of 7% by volume. Sprinklers each discharging 30 L/min,
are used at 12.2 m spacing. Lateral spacing is 12.2 m. The irrigation efficiency is 70% and
irrigation starts with 50% depletion of soil water reservoir. (25 marks)
Determine
a) The total available soil water (moisture) capacity of the soil.
b) The gross depth of water to be applied during each irrigation.
c) The irrigation cycle.
d) The quantity of water needed from the source, if the sprinkler system operates
12 hours/day each day during the irrigation cycle.
e) The rate of application of irrigation water.
2. a) What is subsurface irrigation? Differentiate between natural and the artificial sub
surface irrigation. Is the drip system also a subsurface irrigation? (10 marks)
b) Find the time required to cover an area of 0.15 ha of the border strip by a stream
with a discharge of 0.04m3
/s. The average depth of flow over the strip is 80 mm
and the average infiltration rate is 40 mm/hr. Find the maximum area that can be
irrigated by the same discharge. (15 marks)
3. An area of 10 ha is to be irrigated by a pumping system working for 10 hours a day.
The available moisture holding capacity of the soil is 160 mm/m and the root zone
depth is 1.2 m. Irrigation is to be done when 50 % of the available moisture in the

root zone is depleted. Water application efficiency is 70%. Peak rate of moisture
use by crops is 4 mm per day. Losses in the water conveyance system are
negligible. (25 marks)
Determine: (i) The net depth of water application
(ii) The irrigation interval
(iii) The depth of water to be pumped per application and the
required system's capacity
4. A typical orchard is to be developed on a field with dimensions of 253m by 439 m.
The orchard will be irrigated using a drip system laid out so that each tree is served
by 4 emitters. The following design conditions are based on peak period
requirements at full tree maturity:
Operating pressure head at the emitter = 10 m
Peak period crop water requirement = 5 mm/day
Emission Uniformity (distribution pattern efficiency)= 92%
Operating time = 18 hours/day
Estimate the following design parameters: (25 marks)
a) Number of emitters required.
b) Required emitter discharge, L/hr
c) Length of the lateral, m
TEST
AE 313/IRWE 317
THIRD YEAR
AGRICULTURAL/IRRIGATION AND WATER RESOURCES ENGINEERING
STUDENTS

Date: January 2013
Q1 A 10 ha cropped field (peak crop evapotranspiration is 5 mm/day and rooting depth of
0.915 m) has been irrigated by a hand moved portable sprinkler irrigation system. The soil
in this field is loam with field capacity soil moisture content (θfc) of 21% by volume and
wilting point water content (θwp)of 7% by volume. Sprinklers each discharging 30 L/min,
are used at 12.2 m spacing. Lateral spacing is 12.2 m. The irrigation efficiency is 70% and
irrigation starts with 50% depletion of soil water reservoir.
Determine
a) The total available soil water (moisture) capacity of the soil.
b) The gross depth of water to be applied during each irrigation.
c) The irrigation cycle.
d) The quantity of water needed from the source, if the sprinkler system operates
12 hours/day each day during the irrigation cycle.
e) The rate of application of irrigation water.
Q2 A typical orchard is to be developed on a field with dimensions of 253m by 439 m. The
orchard will be irrigated using a drip system laid out so that each tree is served by 4
emitters. The following design conditions are based on peak period requirements at full
tree maturity:
Operating pressure head at the emitter = 10 m
Peak period crop water requirement = 5 mm/day
Emission Uniformity (distribution pattern efficiency)= 92%
Operating time = 18 hours/day
Estimate the following design parameters: (25 marks)
d) Number of emitters required.
e) Required emitter discharge, L/hr
f) Length of the lateral, m

Q3 (a) Explain the effect of change of speed and impeller diameter on pump performance.
head of 62.0 m. The impeller diameter is 25.0cm and it is rotated at 1750rpm. A
requirements.
and the shaft horsepower necessary to drive the modified pump.
is re-installed.
Q4 (a) The terms consumptive use and evapotranspiration are the same. Discuss.
(b) An area of maize plants has an average rooting depth of 0.7m. The soil has a field
capacity of 35 percent by weight, a permanent wilting point of 18 percent by weight
and a dry bulk density of 1.58. A soil moisture sample weighed 61.4 g and after
oven drying 53.6 g. What depth of irrigation water should be applied to the root
zone in order to replenish the soil moisture level to field capacity?

UNIVERSITY EXAMINATION (SEMESTER 5)
AE 313
THIRD YEAR
Time 3 hours
systems. (10 Marks)
b) If the conventional peak ETc is 9.0 mm/day and 75% of the area is shaded by
trees in an orchard, determine the design ETc rate, volume of water required
per tree per day, and application rate in L/h per tree for a drip irrigation system.
Assume EU = 0.93, a tree spacing of 3 x 6 m, 22 h/day operation and irrigation
interval of 2 days. Also, determine the number of emitters required per tree.
Assume a medium textured soil of low density, a 1.5 m root zone and 45% of
the area is to be irrigated. Hint: Make use of Table 1. (15 Marks)

Varying Layers
________________________________
Depth 0.75m
Coarse 0.45 0.75 1.05
Medium 0.90 1.2 1.5
Fine 1.05 1.5 1.8
Depth 1.5m
Coarse 0.75 1.4 1.8
Medium 1.2 2.1 2.7
Fine 1.5 2.0 2.4
Q2. (a) Why is the moisture content at which a crop permanently wilts a function of
consumptive-use rate as well as soil texture? (10 marks)
(b) A farmer having 20 hectares of land grows wheat in 10 hectares, potatoes in 4
hectares, peas in 2 hectares and onions in 4 hectares during dry season. The
irrigating season is 4 months. The water requirements of wheat, potatoes, peas and
onions are 45 cm, 50 cm, 15 cm and 10 cm, respectively. What size of irrigation
stream will be required from a source which can supply for 10 hours each day during

the season? (15 marks)
Q3 (a) Briefly describe one method of operating a sprinkler system when the period
between irrigations is greater the computed irrigation interval. (8 marks)
b) A grower’s field has 22 cm of available water. The management allowable deficit
is 40 per cent. During the peak period, the crop evapotranspiration is 8 mm/day.
The grower wants to allow one day without operations for each irrigation interval
during peak period and operates two sets per day. The hand-move sprinkler
irrigation system has 1180 m of main line with valves (hydrants) at both ends and
every 20 m. How many laterals are required to irrigate the system? (17 marks)
Q4 (a) Explain the effect of change of speed and impeller diameter on pump performance.
(5marks)
head of 61.5m The impeller diameter is 26.0cm and it is rotated at 1800rpm. A
requirements.
and the shaft horsepower necessary to drive the modified pump(10 marks).
is re-installed (10 marks).

AE 313
THIRD YEAR
Time 3 hours
Q1 a) Explain advantages and disadvantages of drip irrigation system compared to those
of sprinkler irrigation system.
b) A typical orchard is to b developed on a field with dimensions of 250m by 450m.
The orchard will be irrigated using a trickle system laid out so that each tree is
served by four emitters. The following design conditions are based on peak period
requirements at full tree maturity:
 Operating pressure head at the emitter = 15m
 Peak period crop water requirement = 6mm/d
 Distribution pattern efficiency = 92 percent
 Operating time = 22 h/d
Estimate the following design parameters:
i) Number of emitters required
ii) Required emitters discharge (L/h)
iii) Length of lateral (m).

Table 1: General estimates of trickle system equipment requirements
Type of Crop Row
Spacing
(m)
Plants per
Hectare
Emitters
per
Hectare
Lateral
Length
(m)/ha)
Ordinary orchards 6 250 500 -
1,500
1,900
Dwarf orchards and
vineyards
3.7 1,000 2,000 3,040
Berries and wide-
spaced row crops
1.5 15,000 7,500 6,840
Greenhouse and close
– spaced row crops
1 25,000 10,000 10,640
1.00 g/cm3
.
percent water content.
from the top 45 cm to increase the air filled porosity to 25.0 percent?
Q3 (a) Outline what you understand about pump characteristic curves and their respective
importance in pump selection
(b) A test on a centrifugal pump to be used in an irrigation farm supplied the following
results:

Discharge Q (m3
/s) 0 0.080 0.25 0.29 0.32
Total pressure head
H (m)
45 42.0 38.0 29.0 16.0
The pump is connected to a suction pipe, length 3.0m and a discharge pipe, length
40m, each with diameter 250mm. Water is pumped from a level of 1.0m below the
pump's centre line and is discharged at a level of 17.0m above the centre line of the
pump. Assume f = 0.0015, determine the flow rate in m3
/hr
Q4 a) i) State three major conditions which tend to satisfy irrigation farmers with
low water application efficiency
ii) State three major conditions which tend to stimulate irrigation farmers to
attain high water application efficiency
b) Determine the required capacity of a sprinkler system to apply water at the rate of
13mm/hr. Two 186metres long sprinkler lines are required. Sixteen sprinklers are
spaced at 12 - metre intervals on each line. The spacing between lines is 18metres.
Allowing 1 hour for moving each 186 metre sprinkler line, how many hours would
be required to apply a 5cm irrigation to a square 16hectors field? How many days
are required assuming 12hour days?

AE 313/IRWE 317
THIRD YEAR
Time 3 hours
Q1 a) Briefly discuss the stages that are involved in estimating a pump capacity. (9
marks)
b) A sprinkler irrigation system is to be designed to irrigate 8 ha of vegetables in
deep silt loam soil in moderate dry climate. The field is flat. Determine the
limiting rate of application, irrigation period, the net depth of water per
application, the depth of water pumped per application and the required system
capacity in hectare-centimetres per day. If the system is operated for 15 hours
each day, determine the pump capacity in litres/second. (16 marks)
Assumptions: Irrigation starts at 50% moisture depletion level
Water application efficiency is 75%
Hint: Make use of Tables 1, 2, 3 and 4
Table 1: Range of available water holding capacity of soils

Table 2: Effective root zone depth of some common crops (grown on very deep, well
drained soils)
Rooting characteristics
Shallow
rooted
Moderately
deep rooted
Deep
rooted
Very deep
rooted
Depth of root zone
60cm 90cm 120cm 180cm
Rice Wheat Maize Sugarcane
Potato Tobacco Cotton Citrus
Cauliflower Castor Sorghum Coffee
Cabbage Groundnut Pearl
millet
Apple
Lettuce Muskmelon Soya bean Grapevine
Onion Carrots Sugar beet Safflower
Pea Tomato Lucerne
Bean
Chilli
Soil type Percent moisture, based on dry
weight of soil
Depth of
available water
per unit of soil
Field
Capacity
Permanent
wilting point
percentage
Cm per metre
depth of soil
Fine sand 3-5 1-3 2-4
Sandy
loam
5-15 3-8 4-11
Silt loam 12-18 6-10 6-13
Clay
loam
15-30 7-16 10-18
Clay 25-40 12-20 16-30

Table 3: Maximum rates of soil moisture use by crops under different climatic
conditions
Table 4: Suggested maximum application rates for sprinklers for average soil, slope and tilth
S/No Soil texture and
profile
0-5% slope 5-8% slope 8-12% slope 12-16%
slope
cm/hr cm/hr cm/hr cm/hr
1 Course sandy soils to
2m
5.0 3.7 2.5 1.3
2 Course sandy soils
over more compact
soils
3.7 2.5 2.0 1.0
3 Light sandy loams to
2m
2.5 2.0 1.5 1.0
4 Light sandy loams
over more compact
soils
2.0 1.3 1.0 0.8
5 Silt loams to 2m 1.3 1.0 0.8 0.5
6 Silt loams over more
compact soils
0.8 0.6 0.4 0.3
7 Heavy textured clays
or clay loams
0.4 0.3 0.2 0.1
Climatic
Conditions
Peak rate of soil moisture
removal (mm/day)
Cool, humid 3
Cool, dry 4
Moderate, humid 4
Moderate, dry 5
Hot, humid 5
Hot, dry 8

Q2 a) Define irrigation frequency and explain how to estimate it. (10 marks)
b) Determine the seasonal consumptive use and net irrigation water requirements for
a crop from the following data: (15 marks)
Month Pan
evaporation
(cm)
Consumptive
use
coefficient
Effective
precipitation
(cm)
November 20 0.45 3.0
December 22 0.50 4.0
January 24 0.80 3.5
February 26 0.85 2.0
Q3 a) Level borders have been used for irrigation relatively flat lands in areas not strictly
arid or humid. Explain why heavy rains would create a problem? (10 marks)
b) A maize crop is to be irrigated by check basin method. The size of each basin is
10m x 8m. The size of the available stream is 18L/s. The water holding capacity of
the root zone soil is 16%. The dry bulk density of the soil is 1.58g/cc. Soil moisture
content before irrigation is 8.5% by weight. Determine the irrigation duration if the
water application efficiency is 96%. The depth of the root zone is 80cm. (15 marks)
Q4 If the conventional peat ET is 8.0mm/day and 80 percent of the area is shaded by trees in
an orchard, determine the design ET rate, volume of water required per tree per day, and
application rate in L/h per tree for a micro-irrigation system. Assume EU = 0.90, a tree
spacing of 3 x 6m, 18 h/day operation, and irrigation interval of 2 days. (25 marks)

AE 313/IRWE 317
THIRD YEAR
Time 3 hours
Q1 a) Briefly discuss the stages that are involved in estimating a pump capacity.
b) A sprinkler irrigation system is to be designed to irrigate 8 ha of vegetables in
deep silt loam soil in moderate dry climate. The field is flat. Determine the
limiting rate of application, irrigation period, the net depth of water per
application, the depth of water pumped per application and the required system
capacity in hectare-centimetres per day. If the system is operated for 15 hours
each day, determine the pump capacity in litres/second.
(Q1 Test 201 1998/99 Hort students)
Table 1: Range of available water holding capacity of soils
Soil type Percent moisture, based on dry
weight of soil
Depth of
available water
per unit of soil
Field
Capacity
Permanent
wilting point
percentage
Cm per metre
depth of soil
Fine sand 3-5 1-3 2-4
Sandy
loam
5-15 3-8 4-11
Silt loam 12-18 6-10 6-13
Clay
loam
15-30 7-16 10-18

Table 2: Effective root zone depth of some common crops (grown on very deep,
well drained soils)
Rooting characteristics
Shallow
rooted
Moderately
deep rooted
Deep
rooted
Very deep
rooted
Depth of root zone
60cm 90cm 120cm 180cm
Rice Wheat Maize Sugarcane
Potato Tobacco Cotton Citrus
Cauliflower Castor Sorghum Coffee
Cabbage Groundnut Pearl
millet
Apple
Lettuce Muskmelon Soya bean Grapevine
Onion Carrots Sugar beet Safflower
Pea Tomato Lucerne
Bean
Clay 25-40 12-20 16-30

Chilli
Table 3: Maximum rates of soil moisture use by crops under different climatic
conditions
Table 4: Suggested maximum application rates for sprinklers for average soil, slope and tilth
S/No Soil texture and
profile
0-5% slope 5-8% slope 8-12% slope 12-16%
slope
cm/hr cm/hr cm/hr cm/hr
1 Course sandy soils to
2m
5.0 3.7 2.5 1.3
2 Course sandy soils
over more compact
soils
3.7 2.5 2.0 1.0
3 Light sandy loams to
2m
2.5 2.0 1.5 1.0
4 Light sandy loams
over more compact
soils
2.0 1.3 1.0 0.8
5 Silt loams to 2m 1.3 1.0 0.8 0.5
6 Silt loams over more 0.8 0.6 0.4 0.3

compact soils
7 Heavy textured clays
or clay loams
0.4 0.3 0.2 0.1
Q2 a) Define irrigation frequency and explain how to estimate it. (9 marks)
c) Determine the seasonal consumptive use and net irrigation water requirements for
a crop from the following data: (Source AE 302, 2011 Irrigation and drainage Q1)
Month Pan
evaporation
(cm)
Consumptive
use
coefficient
Effective
precipitation
(cm)
November 20 0.45 3.0
December 22 0.50 4.0
January 24 0.80 3.5
February 26 0.85 2.0
Q3 a) Level borders have been used for irrigation relatively flat lands in areas not strictly
arid or humid. Explain why heavy rains would create a problem?
b) A maize crop is to be irrigated by check basin method. The size of each basin is
10m x 8m. The size of the available stream is 18L/s. The water holding capacity of
the root zone soil is 16%. The dry bulk density of the soil is 1.58g/cc. Soil moisture
content before irrigation is 8.5% by weight. Determine the irrigation duration if the
water application efficiency is 96%. The depth of the root zone is 80cm. (Q4 Test
201 1998/99 Hort students)
Q4 If the conventional peat ET is 8.0mm/day and 80 percent of the area is shaded by trees in
an orchard, determine the design ET rate, volume of water required per tree per day, and
application rate in L/h per tree for a micro-irrigation system. Assume EU = 0.90, a tree
spacing of 3 x 6m, 18 h/day operation, and irrigation interval of 2 days. (Test AE 313
2007/2008 Q3 )
AE 313/IWRE 317

THIRD YEAR
AGRICULTURAL ENGINEERING AND IRRIGATION AND WATER RESOURCES
ENGINEERING STUDENTS
September 2013
Q1 a) Smallholder farmers want to grow horticultural crops as a joint venture. In the process
of developing the farm, they discovered that they need to by a centrifugal pump that that
has a water horsepower of 11 hp that will pump water against a total head of 28m.
Determine the rate at which the pump is lifting the water. If the pump has a shaft
horsepower of 14 hp at what efficiency is it operating? (15 marks)
b) If the pump is driven by an electric motor which has an efficiency of 90%, what is the
cost of electrical energy per unit (kw-hour)? Assume that the pump is operating for 10
hours daily for 20 days in a month and the cost of the electrical energy for a month is Tshs
15,000,000. (10 marks)
Q2 (a) Gravitational, capillary and hygroscopic are three classes of moisture in the soil.
Discuss the classes in relation to soil properties. (9 marks)
(b) Ten-250 m long laterals with sprinklers in a 18 m square spacing pattern are
operated simultaneously to irrigate a 25 ha field. The system delivers a daily
irrigation water requirement of 8 mm per day and the frequency of irrigation is 12
days. Determine the depth of irrigation water application to the field. (16 marks)
Q3 (a) Define irrigation frequency and explain how to estimate it. (8 marks)
(b) An area of 20 ha is to be irrigated by a pump which is operated daily. Irrigation is
done when the moisture content in the root zone is depleted. The peak rate of
moisture use by crops is 8 mm/day. The conveyance losses are negligible, irrigation
interval is 20 days, gross depth of water application is 230 mm and the required
capacity of the irrigation system is 30 L/s. Determine the moisture holding capacity
of the soil, the irrigation water application efficiency and the duration of irrigation
per day. (17 marks)
systems. (9 marks)

d) If the conventional peak ETc is 9.0 mm/day and 75% of the area is shaded by trees
in an orchard, determine:
(i) The design ETc rate, (4 marks)
(ii) Volume of water required per tree per day, (4 marks)
(iii) Application rate in L/h per tree. (4 marks)
(iv) The number of emitters required per tree. (4 marks)
Assume: - EU = 0.93,
- A tree spacing of 3 x 6 m,
- 22 h/day operation
- Irrigation interval of 2 days.
- A medium textured soil of low density,
- A 1.5 m root zone and
- 45% of the area is to be irrigated.
Hint: Make use of Table 1.
Varying Layers
________________________________
Depth 0.75m
Coarse 0.45 0.75 1.05
Medium 0.90 1.2 1.5
Fine 1.05 1.5 1.8

Depth 1.5m
Coarse 0.75 1.4 1.8
Medium 1.2 2.1 2.7
Fine 1.5 2.0 2.4
IWRE 317
DESIGN OF IRRIGATION SYSTEMS
THIRD YEAR
IRRIGATION AND WATER RESOURCES ENGINEERING/AGRICULTURAL
ENGINEERING STUDENTS
Time: 3 hours
FERBRUARY 2018

Q1 a) What are the factors that influence the consumptive use of water for any crop and
how is consumptive use related to the total crop water requirement? (10 marks)
b) A field is to be irrigated with a sprinkler system. The root zone is 1.3 m deep and the
available moisture holding capacity of the soil is 160 mm/meter depth. The field is to
be irrigated when 50% of the available moisture capacity is depleted. The gross depth
of water that has to be pumped per application is 130 mm and the area to be irrigated
par day is 0.7 ha. The whole field is covered after 17 days. Determine the net depth of
water application per irrigation, the peak rate of moisture use par day, the water
application efficiency and the total area irrigated. (30 marks)
Q2 a) Describe what is meant by advance curve and a cut-back stream in an irrigation furrow
system. (10 marks)
b) Determine the size of the irrigation stream required to irrigate an area of 15 ha in a
region having no effective rainfall and where the peak consumptive use is 5 mm/day.
The irrigation system is operated for 12 hours each day. The field irrigation efficiency
is 50 per cent. (20 marks)
Q3 a) A farmer is using a drip irrigation system to irrigate fruits and vegetable crops. The
system worked well in the beginning but now the spatial application is not uniform.
Preliminary investigations showed that there is a problem of clogging in the system.
Describe the possible causes of clogging of emitters and pipelines in his drip irrigation
system. (15 marks)
b) Determine the emission uniformity for large long-path emitters if the manufacturer’s
coefficient of variation is 0.15. There are four emitters per plant. The average operating
pressure is 90 kPa and the minimum pressure is 80 kPa. Hint: make use of Fig. 1. (15
marks)

Fig. 1: Discharge of various emitters versus pressure head. Values of K and x are for pressure in
kPa and flow in L/h
HOMEWORK
AE:201
SECOND YEAR
AGRICULTURE GENERAL AND AGRONOMY STUDENTS

Q 1.0 (a) Define the following terms:
a) Consumptive use of a crop
b) Irrigation interval
c) Peak irrigation water requirement
(b) An experienced farmer in Majengo irrigation scheme in Mbeya region found out that the
average volumetric moisture content in the root zone depth of 1.20 mm will correspond quite
reasonably with moisture content at field capacity of 34%, two days after completing an irrigation
event. The daily consumptive use is 9 mm during the hottest month of the season. During this
period, what will be the average volumetric moisture content 10 days after completing an irrigation
event? If the management allowed deficit is 80 mm, what is the required interval between irrigation
events during the hottest month? What is the required irrigation interval when the daily
consumptive use is 6 mm?
Q 2.0 (a) Explain in detail the conditions that will allow you to use a centrifugal pump and
the problems you might encounter in the process of using it.
(b) A sprinkler irrigation system requires a centrifugal pump to operate. It was found out that
a small centrifugal pump with a discharge of 0.046 m3
/s could pump the irrigation water at a head
of 24 m if it is operating with an efficiency of 80 %. It was also found that at this head, it requires
17.8 kW at 1400 rpm. Assuming the efficiency of the pump remains constant, what is the
theoretical discharge of the pump if its speed is increased to 2000 rpm? What is the theoretical
head and horsepower at 2000 rpm?
Q 3.0 (a) Explain the difference you would expect in root systems of crops which have been
irrigated by widely-spaced, heavy irrigations and frequent, light irrigations.
(b) Determine the water-applications efficiency and distribution uniformity if a stream of 100
L/s was delivered to the field for 2.5 hours, runoff averaged 55 L/s for 1 hour and depth of
penetration of the water varied from 1.8 m at the upper end to 1.2 m at the lower end of the field.
The root-zone depth is 1.8 m

Q 4.0 (a) How can the knowledge of the source of irrigation water be useful in solving a
drainage problem?
(b) An infrequent irrigation is practiced at the horticultural unit of the University whenever
oranges are irrigated. The soils at the orange farm are clay loam with a drainable porosity of 0.05,
a hydraulic conductivity of 0.7m/day and an impervious layer 2.2 m below the drains. Drainage
requirements for the orange trees are such that the initial water table depth below the surface is
0.20 m with a rate of drop of 0.25 m for the first day. Because of outlet depth, the maximum depth
of the drain is limited to 1.3 m measured to the bottom of the 125 mm drains. Compute the drain
spacing.
TEST
AE:201
SECOND YEAR
1 (a) Briefly describe one method of operating a sprinkler system when the period
between irrigations is greater the computed irrigation interval.
(b) An area of 10 ha is to be irrigated by a pumping system working for 10 hours a day. The
available moisture holding capacity of the soil is 160 mm/m and the root zone depth is 1.2 m.
Irrigation is to be done when 50 % of the available moisture in the root zone is depleted. Water

application efficiency is 70%. Peak rate of moisture use by crops is 4 mm per day. Losses in the
water conveyance system are negligible.
Determine:
(i) The net depth of water application
(iii) The depth of water to be pumped per application and the required system's capacity
2 (a) Why is accurate information regarding water supply important to the development
of an irrigation system (Israelsen page 417 chap. 2 number 1)
(b) During periods of peak water use, water is diverted from an irrigation canal into a storage
reservoir at a rate of 0.8 m3
/s one day/week (water is distributed to other irrigators along the canal
during the remaining days of the week). Water is conveyed from the reservoir to a 50-ha field in
a 2000-m long unlined ditch. The field is irrigated continuously during peak water use periods.
Determine:
(i) the reservoir storage efficiency;
(ii) the conveyance efficiency;
(iii) the application efficiency; and
(iv) the overall irrigation efficiency
for the following conditions:
. the average daily irrigation requirement during peak water use periods is 10 mm/day
. seepage and evaporation losses in the unlined ditch total 1.0L/min/m
. total seepage and evaporation losses from the reservoir are 100L/min (James page 107
number 2.8)
3 (a) What properties of the soil determine the percentages of these three classes of
moisture in the soil: hygroscopic, capillary, and gravitational ? (Israelsen page 422 number 7)
(b) A maize crop needs to be irrigated in the near future. Its root depth is 0.8 m and the soil in
which it is growing is a clay loam with a total available water (TAW) of 15 cm/m. An irrigation

service estimates that the average evapotranspiration for maize over the next 7 days should be 12
mm/day. The irrigator wishes the management allowed deficit (MAD) to be no greater than 60 %
and no less than 50 % of TAW. A student visited the field today and took a gravimentric soil
sample 30 cm long and 2.5 cm in diameter. It weighed 260 gm in the laboratory. She found that
the volume of water necessary to saturate the sample after it had been oven dried was 58.9 cm3
.
The specific weight of the soil particles was 2.65 gm/cm3
. She put a 1/3 atmosphere pressure on
the saturated sample until drainage stopped and found that the sample had lost 24.7 gm of water.
How many days until the irrigator should expect to irrigate?
4 (a) Explain why the need for surface drainage increases as the annual rainfall increases
(b) Consider a land near the University farm is used for vegetable growth. The hydraulic
conductivity values for the soil profile are 0 - 1.25 m depth: 0.9m/day and 1.25 - 2.50 m depth:
1.6m/day. Below 2.5 m, the soil profile is impervious. The pipe drain depth is limited to 1.25 m
by the outfall conditions and the water table depth required is 0.75 m. Daily rainfall for vegetable
crops and normal under-drainage is 13 mm/day. With the help of Table1; compute the drain
spacing

HOMEWORK
AE:201
SECOND YEAR
Q1.0 (a) i) Briefly explain how to measure the consumptive use of field crops
ii) Briefly explain three different methods that are used to estimate consumptive use of a
particular crop
(b) The root zone of a certain soil has a field capacity of 180 mm and a wilting point of 100
mm. The consumptive use of crops in July is 6 mm/day. Assuming no rainfall, how often ought
a farmer to irrigate? How much water should be applied at each irrigation if there is to be no deep
percolation?
Q2.0 (a) Discuss in detail what is meant by the term water application efficiency and how is
it different from water storage efficiency
(b) A 75 mm application of water measured at the pump increased the average water
content of the top 0.6 m of soil from 18 % to 23 % by weight. If the average dry bulk density is
1.2, what is the water application efficiency?
Q3.0 (a) Write short notes on the methods used to estimate the depth and spacing of drainage
systems
(b) Determine the depth and spacing of drains to maintain a constant water table 1.5 m
below assuming that the height of the water table at the mid-plane is 0.5 m above the centre of 150
mm drains. The average hydraulic conductivity of the soil is 0.6 m/day, the depth D to the
impervious layer is 3 m, and the excess irrigation rate is 3 mm/day per metre length. Assume a

spacing of 40 m to select the equivalent depth.
Q4.0 (a) Outline what you understand about the term pump characteristic curves and their
respective importance in pump selection
(b) A test on a centrifugal pump to be used in an irrigation farm supplied the following results:
Discharge Q (m3
/s) 0 0.079 0.158 0.238 0.317
Total pressure head
H (m)
44.5 42.3 37.4 28.6 15.3
The pump is connected to a suction pipe, length 2.5 m and a discharge pipe, length
40 m, each with diameter 200 mm. Water is pumped from a level of 1.5 m below
the pump's centre line and is discharged at a level of 16.5 m above the centre line
of the pump. Assume f = 0.0015, determine the flow rate in m3
/hr
Q5.0 (a) Explain detail the term Maximum Practical Suction Lift of a
centrifugal pump
(b) The graph shows the characteristic curves of a centrifugal pump for various
impeller diameters. The pump is connected to a pipe system of which the system
curve Hsys = 35 + 16,000Q2
(Hsys in m and Q in m3
/s). Determine what will be
the flow rate as well as the power required, if the impeller diameter is 190 mm.
(Source South africa book)
Q6.0 (a) Briefly discuss the stages involved before in the estimation of a
pump capacity.
(b) A sprinkler irrigation system is to be designed to irrigate 8 ha of vegetables
in deep silt loam soil in moderate dry climate. The field is flat. Determine the
limiting rate of application, irrigation period, the net depth of water per application,
the depth of water pumped per application and the required system capacity in
hectare-centimetres per day. If the system is operated for 15 hours each day,
determine the pump capacity in litres/second.

Hint: Make use of Tables 1, 2 and 3
(source michael pg 651)
Q7.0 (a) Describe what is meant by advance curve and a cut-back in a
irrigation furrow system.
(b) The following data was obtained from a test furrow in a sand soil.
Stream size
(litres/min)
Distance
(m)
Advance time
(min)
Wetted
perimeter
(cm)
Furrow
cross-sectional
area
corresponding
to depth of flow
(cm2
)
92.00 20
40
60
1.75
5.75
10.91
25.39
25.82
26.39
60.00
93.00
103.00

80
100
110
17.83
23.67
27.75
26.70
27.11
27.42
108.40
111.65
112.28
Compute the accumulated infiltrated depth of the furrow
(Source Michael pg 619)
Q8.0 (a) Discuss the following terms:
i) Net irrigation water requirement,
ii) Seasonal irrigation water requirement, and
iii) Readily available moisture.
(b) A stream of 135 litres per second was diverted from a canal and 100 litres per second were
delivered to the field. An area of 1.6 hectares was irrigated in 8 hours. The effective depth of root
zone was 1.8 m. The run off loss in the field was 432 m3
. The depth of water penetration varied
linearly from 1.8 m at the head end of the field to 1.2 m at the tail end. Available moisture holding
capacity of the soil is 200 mm/m depth of the soil. Determine the water conveyance efficiency,
water application efficiency, water storage efficiency and water distribution efficiency, if
irrigation was started at a moisture extraction level of 50 % of the available moisture
(Source Michael pg 549)
Q9.0 (a) Explain the importance of determining the following irrigation efficiencies:
(i) Water conveyance efficiency,
(ii) Water application efficiency,
(iii) Water storage efficiency, and
(iv) Water distribution efficiency.
(b) During periods of peak water use, water is diverted from an irrigation canal into a storage
reservoir at a rate of 0.8 m3
/s one day/week (water is distributed to other irrigators along the canal

during the remaining days of the week). Water is conveyed from the reservoir to a 50-ha field in
a 2000-m long unlined ditch. The field is irrigated continuously during peak water use periods.
Determine:
(i) the reservoir storage efficiency;
(ii) the conveyance efficiency;
(iii) the application efficiency; and
(iv) the overall irrigation efficiency
for the following conditions:
. the average daily irrigation requirement during peak water use periods is 10 mm/day
. seepage and evaporation losses in the unlined ditch total 1.0L/min/m
. total seepage and evaporation losses from the reservoir are 100L/min (James page 107
number 2.8)
Q10.0 (a) Outline areas that requires the installation of a drainage system and why?
(b) An infrequent irrigation is practised at the horticultural unit of the University whenever
a hydraulic conductivity of 0.7m/day and an impervious layer 2.2 m below the drains.Drainage
spacing.

HOMEWORK
AE:201
SECOND YEAR
particular crop
percolation?
Discharge Q (m3
/s) 0 0.079 0.158 0.238 0.317
Total pressure head
H (m)
44.5 42.3 37.4 28.6 15.3
The pump is connected to a suction pipe, length 2.5 m and a discharge pipe, length 40 m, each
with diameter 200 mm. Water is pumped from a level of 1.5 m below the pump's centre line and
is discharged at a level of 16.5 m above the centre line of the pump. Assume f = 0.0015, determine
the flow rate in m3
/hr

Q3.0 (a) Describe what is meant by advance curve and a cut-back in a irrigation furrow
system.
Stream size
(litres/min)
Distance
(m)
Advance time
(min)
Wetted
perimeter
(cm)
Furrow
cross-sectional
area
corresponding
to depth of flow
(cm2
)
92.00 20
40
60
80
100
110
1.75
5.75
10.91
17.83
23.67
27.75
25.39
25.82
26.39
26.70
27.11
27.42
60.00
93.00
103.00
108.40
111.65
112.28
a hydraulic conductivity of 0.7m/day and an impervious layer 2.2 m below the drains.Drainage

spacing.
HOMEWORK
AE:201
SECOND YEAR
HORTCULTURE STUDENTS
Q2.0 (a) Explain detail the term Maximum Practical Suction Lift of a centrifugal pump
(b) The graph shows the characteristic curves of a centrifugal pump for various impeller
diameters. The pump is connected to a pipe system of which the system curve Hsys = 35 +
16,000Q2
/s). Determine what will be the flow rate as well as the power
required, if the impeller diameter is 190 mm.

Q3.0 (a) Briefly discuss the stages involved before in the estimation of a pump capacity.
(b) A sprinkler irrigation system is to be designed to irrigate 8 ha of vegetables in deep silt
loam soil in moderate dry climate. The field is flat. Determine the limiting rate of application,
irrigation period, the net depth of water per application, the depth of water pumped per application
and the required system capacity in hectare-centimetres per day. If the system is operated for 15
hours each day, determine the pump capacity in litres/second.
Q4.0 (a) Write short notes on the methods used to estimate the depth and spacing of drainage
systems
(b) Determine the depth and spacing of drains to maintain a constant water table 1.5 m
below assuming that the height of the water table at the mid-plane is 0.5 m above the centre of 150
mm drains. The average hydraulic conductivity of the soil is 0.6 m/day, the depth D to the
impervious layer is 3 m, and the excess irrigation rate is 3 mm/day per metre length. Assume a
spacing of 40 m to select the equivalent depth.

TEST
AE:201
SECOND YEAR
Q 1. (a) Explain the factors that have to be taken into consideration when designing a furrow
irrigation system.
(b) Furrows 90 m long and spaced at 75 cm apart are irrigated by an initial furrow stream of 2
L/S. The initial furrow stream reached the lower end of the field in 50 minutes. The size of the
stream was the reduced to 0.5 L/S. The cut back stream continued for 1 hour. Estimate the average
depth of irrigation.
Consumptive use of a crop
Irrigation interval
Peak irrigation water requirement
(b) An area of 10 ha is to be irrigated by a pumping system working for 10 hours a day. The
available moisture holding capacity of the soil is 160 mm/m and the root zone depth is 1.2 m.
Irrigation is to be done when 50 % of the available moisture in the root zone is depleted. Water
application efficiency is 70%. Peak rate of moisture use by crops is 4 mm per day. Losses in the
water conveyance system are negligible.

Determine: (i) The net depth of water application
(iii) The depth of water to be pumped per application and the required system's capacity
Q 3.0 (a) Explain in detail the term Maximum Practical Suction Lift of a centrifugal pump.
(b) The graph shows the characteristic curves of a centrifugal pump for various impeller
diameters. The pump is connected to a pipe system of which the system curve Hsys = 35 + 16,000Q2
/s). Determine what will be the flow rate as well as the power required, if
the impeller diameter is 190 mm.
Q 4.0 (a) Write short notes on how to estimate the depth and spacing of drainage systems.
(b) Consider a land near the University farm is used for vegetable growth. The hydraulic
conductivity values for the soil profile are 0 - 1.25 m depth: 0.9m/day and 1.25 - 2.50 m depth:
1.6m/day. Below 2.5 m, the soil profile is impervious. The pipe drain depth is limited to 1.25 m
by the outfall conditions and the water table depth required is 0.75 m. Daily rainfall for vegetable
crops and normal under-drainage is 13 mm/day. With the help of Table 1; compute the drain
spacing

EXAMINATION
AE:302
THIRD YEAR
HORTICULTURE STUDENTS
Q1 (a) (i) Briefly explain what is meant by priming a centrifugal pump.
(ii) State four different techniques that are used to prime centrifugal pumps.
(b) Determine the annual consumption of electrical energy by a motor driven centrifugal pump
installed in a shallow well. The pump discharges is 16 L/s against a total head of 7 m. The pump
efficiency is 70 % and the motor efficiency is 84 %. The drive efficiency may be assumed to be
100 %. The pump is operated for 3500 hours per year.
Q2 (a) Briefly describe one method of operating a sprinkler equipment when the period
between irrigations is greater than the computed irrigation interval.
(b) A 16 ha field is to be irrigated at a maximum rate of 12 mm/hour with a sprinkler system.
The root zone is 1.2 m deep and the available water capacity of the soil is 200 mm/m of depth.
The water application efficiency is 75 % and the soil is to be irrigated when 45 % of the available
water capacity is depleted. The peak rate of water use is 5.0 mm/day. Determine the net depth of
application per irrigation, depth of water to be pumped, days to cover the field and area to be
irrigated per day.

Q 3 (a) Explain why the need for surface drainage increases as the annual rainfall increases.
(b) Consider a land near Lower Moshi irrigation scheme is used for vegetable growth. The
hydraulic conductivity values for the soil profile are 0 - 1.25 m depth: 0.9m/day and 1.25 - 2.50 m
depth: 1.6m/day. Below 2.5 m, the soil profile is impervious. The pipe drain depth is limited to
1.25 m by the outfall conditions and the water table depth required is 0.75 m. Daily rainfall for
vegetable crops and normal under-drainage is 13 mm/day. With the help of Table 1; compute the
drain spacing.
SEPTEMBER, 1998
UNIVERSITY EXAMINATION
AE:201
SECOND YEAR
Q1 (a) Describe the probable difference in root systems of crops which have been irrigated
by frequent, light irrigations and widely spaced, heavy irrigations.
(b) Determine the water application efficiency and distribution uniformity if a stream of 83 L/s
was delivered to the field for 2¼ hours, runoff averaged 45 L/s for 1 hour and the depth of
penetration of the water varied linearly from 1.6 m at the upper end to 1.0 m at the lower end of
the field. The root zone depth is 1.6 m.

Q2 (a) Explain briefly why sprinkler system of irrigation is preferred to surface methods
of irrigation.
(b) Determine the total pumping head for a sprinkler irrigation system on a level land. The
average operating pressure at the nozzle is 3kg/cm2
. The friction loss in the main is 6.5 m and in
the lateral is 4 m; the depth from the centre line of the pump to the water level is 5 m and the
required discharge is 31.6 L/s. The riser height is 1.5 m and friction loss in all valves 3.25 m.
Determine the horsepower requirements of the pump if it operates at 65 % efficiency.
Q3 (a) Write short notes on how to estimate the depth and spacing of drainage systems.
(b) For Lower Moshi irrigation scheme in Kilimanjaro region, compute the drain spacing
assuming the depth to the centre of the drain is 1.9 m and the minimum depth to the water table is
1.6 m. Subsurface explorations indicate a hydraulic conductivity of 0.6 m/day above an impervious
layer at a depth of 6.8 m. The excess irrigation rate is equivalent to a drainage water of 1.3 mm/day.
NOTE: Make use of Figure 1.

SEPTEMBER, 1998
UNIVERSITY EXAMINATION
AE:201
SECOND YEAR
Q1.0 (a) Discuss the following terms:
i)Net irrigation water requirement,
ii)Seasonal irrigation water requirement, and
iii)Readily available moisture.
(b) A stream of 135 litres per second was diverted from a canal and 100 litres per second were
delivered to the field. An area of 1.6 hectares was irrigated in 8 hours. The effective depth of root
zone was 1.8 m. The run off loss in the field was 432 m3
. The depth of water penetration varied
linearly from 1.8 m at the head end of the field to 1.2 m at the tail end. Available moisture holding
capacity of the soil is 200 mm/m depth of the soil. Determine the water conveyance efficiency,
water application efficiency, water storage efficiency and water distribution efficiency, if
irrigation was started at a moisture extraction level of 50 % of the available moisture
Q2.0 (a) Briefly discuss the stages involved in the estimation of a pump capacity.
(b) A sprinkler irrigation system is to be designed to irrigate 8 ha of vegetables in deep silt
loam soil in moderate dry climate. The field is flat. Determine the limiting rate of application,
irrigation period, the net depth of water per application, the depth of water pumped per application
and the required system capacity in hectare-centimetres per day. If the system is operated for 15
hours each day, determine the pump capacity in litres/second.
Assumptions:Irrigation starts at 50% moisture depletion level

a hydraulic conductivity of 0.6m/day and an impervious layer 2 m below the drains. Drainage
spacing. Hint: Make use of Figure 1
SEPTEMBER, 1998
EXAMINATION
HT:302
THIRD YEAR
particular crop
percolation?

Discharge Q (m3
/s) 0 0.079 0.158 0.238 0.317
Total pressure head
H (m)
45 40 36 27 15
The pump is connected to a suction pipe, length 2.6 m and a discharge pipe, length 42 m, each
with diameter 210 mm. Water is pumped from a level of 1.5 m below the pump's centre line and
is discharged at a level of 16.0 m above the centre line of the pump. Assume f = 0.0015, determine
the flow rate in m3
/hr
Q3.0 (a) Describe what is meant by advance curve and a cut-back in a irrigation furrow
system.
Stream size
(litres/min)
Distance
(m)
Advance
time
(min)
Wetted
perimete
r
(cm)
Furrow
cross-sectional
area
corresponding
to depth of flow
(cm2
)
92.00 20
40
60
1.75
5.75
10.91
25.39
25.82
26.39
60.00
93.00

103.00

SUPPLEMENTARY UNIVERSITY EXAMINATION
NOVEMBER, 1998
HT:302
THIRD YEAR
Q 1. (a) Explain the factors that have to be taken into consideration when designing a furrow
irrigation system.
(b) Furrows 100 m long and spaced at 80 cm apart are irrigated by an initial furrow stream of
2.5 L/S. The initial furrow stream reached the lower end of the field in 45 minutes. The size of the
Q 2.0 (a) Explain in detail the conditions that will allow you to use a centrifugal pump and
the problems you might encounter in the process of using it.
(b) A sprinkler irrigation system requires a centrifugal pump to operate. It was found out that
a small centrifugal pump with a discharge of 0.046 m3
/s could pump the irrigation water at a head
of 24 m if it is operating with an efficiency of 80 %. It was also found that at this head, it requires
17.8 kW at 1400 rpm. Assuming the efficiency of the pump remains constant, what is the
theoretical discharge of the pump if its speed is increased to 2000 rpm? What is the theoretical
head and horsepower at 2000 rpm?
Q 3.0 (a) Explain the difference you would expect in root systems of crops which have been

irrigated by widely-spaced, heavy irrigations and frequent, light irrigations.
(b) Determine the water-applications efficiency and distribution uniformity if a stream of 120
L/s was delivered to the field for 2 hours, runoff averaged 50 L/s for 1 hour and depth of penetration
of the water varied from 2. m at the upper end to 1.5 m at the lower end of the field. The root-zone
depth is 2 m.
SUPPLEMENTARY UNIVERSITY EXAMINATION
NOVEMBER 1998
AE:201
SECOND YEAR
Q2.0 (a) Explain detail the term Maximum Practical Suction Lift of a centrifugal pump
(b) The graph (in Fig 1) shows the characteristic curves of a centrifugal pump for various
impeller diameters. The pump is connected to a pipe system of which the system curve Hsys =
34 + 16,000Q2
/s). Determine what will be the flow rate as well as the
power required, if the impeller diameter is 200 mm.
particular crop

percolation?
(b) From previous experience on a particular field it is known that the average volumetric
moisture content in the root zone depth of 650 mm will correspond quite reasonably with moisture
content at field capacity of 0.38, 3 days after completing an irrigation event. The daily
evapotranspiration is 8 mm during the hottest month of the season. During this period, what will
be the average volumetric moisture content 2 weeks after completing an irrigation event? If the
management allowed deficit is 75mm, what is the required interval between irrigation events
during the hottest month? What is the required irrigation interval when the daily evapotranspiration
is 5 mm?
3. (a) Why is it advisable and often necessary to operate the sprinklers for a few minutes
before and after fertilizer is applied? Consider the system, the crop, and the soil.
(b) Determine the required capacity of a sprinkler system to apply water at the rate of 12.5
mm/hr. Two 186 metres long sprinkler lines are required. Sixteen sprinklers are spaced at 12 -
metre intervals on each line. The spacing between lines is 18 metres. Allowing 1 hour for moving
each 186 metre sprinkler line, how many hours would be required to apply a 5 cm irrigation to a
square 16 hectors field? How many days are required assuming 10 hour days?
4. (a) How can knowledge of the source of irrigation water be useful in solving a drainage
problem?
(b) During an irrigation season 110 cm of irrigation and rain water was caught in rain gauge
located in a sprinkler irrigated field. The seasonal water requirement for the crop was estimated to
be 88 cm. Determine the depth of leaching and the leaching fraction. Neglect any changes in soil
water content that may have occurred during the irrigation season.

AE 201
1. (a) Are the terms "Consumptive Use" and "evapotranspiration" the same? Explain.
(b) An area of vine plants has an average rooting depth of 1 m. The soil has a field capacity
of 0.32 by weight and a permanent wilting point of 0.14 by weight and a bulk density of 1.50. A
soil moisture sample weighed 60.13 gm and after oven drying 51.36 gm. What depth of irrigation
water should be applied to the root zone in order to replenish the soil moisture level to field
capacity?

2. (a) Discuss the statement that irrigation and Drainage are complementary practices in
arid regions.
(b) Determine the system capacity for a sprinkler irrigation system to irrigate 16 hectares of
maize crop. Design moisture use rate is 5 mm per day. Moisture replace in soil at each irrigation
is 6 cm. Irrigation efficiency is 70 percent. Irrigation period is 10 days in a 12 day interval. The
system is to .. operated for 20 hours per day.
3. (a) What are the characteristic curves of a pump? Of what value are they?
(b) Determine the annual consumption of electrical energy by a motor driven centrifugal pump
installed in reservoir. The pump discharge 16 L/S against a total head of 7 m. The pump efficiency
is 70% and the motor efficiency is 84%. The drive efficiency may be assumed to be 100%. The
pump is operated for 3500 hours per year.
4. (a) Explain the factors that have to be taken into consideration when designing a furrow
irrigation system.
(b) Furrows 90 m long and spaced at 75 cm apart are irrigated by an initial furrow stream of 2
L/S. The initial furrow stream reached the lower end of the field in 50 minutes. The size of the
HOMEWORK
AE:201
SECOND YEAR
1 (b) From previous experience on a particular field it is known that the average
volumetric moisture content in the root zone depth of 700 mm will correspond quite reasonably
with moisture content at field capacity of 0.40, 3 days after completing an irrigation event. The
daily evapotranspiration is 9 mm during the hottest month of the season. During this period, what
will be the average volumetric moisture content 14 days after completing an irrigation event? If
the management allowed deficit is 80mm, what is the required interval between irrigation events
during the hottest month? What is the required irrigation interval when the daily evapotranspiration

is 6 mm?
2. (a) How can knowledge of the source of irrigation water be useful in solving a drainage
problem?
(b) During an irrigation season 2000 mm of irrigation and rain water was caught in rain gauge
located in a sprinkler irrigated field. The seasonal water requirement for the crop was estimated to
be 1780 mm. Determine the depth of leaching and the leaching fraction. Neglect any changes in
soil water content that may have occurred during the irrigation season.
3 b) Determine the total pumping head for a sprinkler system on level land. The average
pressure at the nozzle is 276 kPa; the friction loss in the main is 6 m, and in the lateral is 3.7 m;
the drawdown of the well is 4.3 m at the required discharge of 32 L/s; the riser height is 1.5 m; and
friction loss in all valves is 3.0 m. Determine the power requirements for the pump if it operates at
65 % efficiency.
4 (b) Determine the required capacity of a sprinkler system to apply water at the rate of
12.5 mm/hr. Two 186 metres long sprinkler lines are required. Sixteen sprinklers are spaced at 12
- metre intervals on each line. The spacing between lines is 18 metres. Allowing 1 hour for moving
each 186 metre sprinkler line, how many hours would be required to apply a 5 cm irrigation to a
square 16 hectors field? How many days are required assuming 10 hour days?
5 b) A tube well having a capacity of 4000L/h operates 20 hours each day during the
irrigation season.How much area can it command if the irrigation interval is 20 days and depth of
irrigation is 7 cm ?
6 b) Determine the size of the irrigation stream required to irrigate an area of 15 ha in a
region having no effective rainfall and where the peak consumptive use is 5 mm/day. The irrigation
system is operated for 12 hours each day. The field irrigation efficiency is 50 per cent.
7 b) An area of 1 ha was irrigated in 10 h with a stream of 30 L/s. Depth of root zone
was 1 m and available moisture holding capacity 16 cm/m. Irrigation was given when 50 % of
available moisture was depleted. Water application efficiency was 60 %. Determine the water
storage efficiency.

Source for 5, 6, and 7 Michael pg 584
8 b) A maize crop is to be irrigated using the check basin method. The size of each basin
is 10 m x 8 m. The size of the available stream is 18L/s. The water holding capacity of the root
zone soil is 16 %. The dry bulk density of the soil is 1.58. Soil moisture content before irrigation
is 8.5 %. Determine the irrigation duration if the water application efficiency is 96 %. The depth
of the root zone is 80 cm.
Michael pg 683
NEW QUESTIONS FOR THE YEAR 1999
1 A farmer having 10 hectares of land grows wheat in 5 hectares, potatoes in 2 hectares, peas
in 1 hectare and onions in 2 hectares during dry season. The irrigating season is 4 months. The
water requirements of wheat, potatoes, peas and onions are 45 cm, 50 cm, 15 cm and 10 cm,
respectively. What size of irrigation stream will be required from a source which can supply for 8
hours each day during the season?
Q4.3 Michael pp 315 Ans. 10.416 lit/sec.
2 An area of 20 hectares is to be irrigated by a pump working for 12 hours a day. The
available moisture holding capacity of the soil is 16 cm/m and the moisture in the root zone is
depleted. Water application efficiency is 70 per cent. Peak rate of moisture use by the crops is 4
mm/day (weighted average). Losses in water conveyance are negligible. Determine the irrigation
period, net depth of water application, depth of water pumped per application, and the required
capacity of the irrigation system in litres per second.
Example 7.10 Michael pp 548
3 A tube well having a capacity of 4000 litres/hr operates 20 hours each day during the
irrigation season. How much area can it command if the irrigation interval is 20 days and depth of
irrigation is 7 cm?
Q 7.2 Michael pp 584
4 Determine the size of the irrigation stream required to irrigate an area of 15 hectares in a
region having no effective rainfall and where the peak consumptive use is 5 mm/day. The irrigation

system is operated for 13 hours each day. The field irrigation efficiency is 50 per cent.
5 A lateral has 12 sprinklers spaced 14 meters apart. The laterals are spaced 20 meters on
the main line. Determine the amount of fertilizer to be applied at each setting when the
recommended fertilizer dose is 80 kg/ha
6 Furrow 100 m long and spaced 90 cm apart and having a slope of 0.2 per cen are irrigated
for 45 minutes by an initial stream of size equal to the maximum non-erosive stream. The stream
size is then reduced to half nad continued for 1 hour 20 minutes. Determine the average depth of
irrigation.
7 A 12-hectare field is to be irrigated at a maximum rate of 1 cm/hr with a sprinkler system.
The root zone is 90 cm deep. The available moisture holding capacity of the soil is 16.5 cm/metre
depth. The water application efficiency is 70 per cent. The field is to be irrigated when 45 per cent
of the aviallable moisture capacity is depleted. The peak rate of moisture use is 5 mm per day.
Determine the net depth of application per irrigation, depth of water to be pumped in centimetres,
days to cover the field and the area irrigated per day.
8 Determine the change in salinity level of the soil due to the evaporation of ground water
over a period of four months, when the depth of ground water evaporated is 11 cm, and its electrical
conductivity is 10 millimhos/cm. The depth of soil influenced by salt accumulation is 30 cm. The
bulk density and saturation per cent of the soil are 1.4 gm/cc and 63 %, respectively. The density
of water is assumed to be 1.0 gm/cc

9 Determine the depth and spacing of drains to maintain a constant water table 1.5m
below the surface assuming that the height of the water table at the midplane is 0.5 m above
the centre of 150-mm drains. The average hydraulic conductivity of the soil is 0.6 m/day the
depth to the impervious layer is 3 m, and the excess irrigation rate is 3.0 mm/day per meter of
length. Assume a spacing of 40 m to select the equivalent depth.
Q14.11 Schwab pp 319
10 Compute the drain spacing for a clay loam soil having a drainable porosity of 0.06, a
hydraulic conductivity of 0.6m/day, and an imprervious layer 2.4 m below the drains. Drainage
requirements for the crop are such that the initial water table depth below the surface is 0.15
m, with a rate of drop of 0.21 m for the first day. Because of outlet depth, the maximum depth
of the drain is limited to 1.2 m measured to the bottom of the 125-mm drains.
Q14.10 Schwab pp 319
11 A 74-mm application of water measured at the pump increased the average water
content of the top 0.6 m of soil from 18 to 23 percent (dry weight basis). If the average dry
density of the soil is 1.2 g/cm3
, what is the water application efficiency?
Q 18.2 Schwab pp 405
12 A flow of 5 m3
/s is diverted from a river into a canal. Of this amount 4 m3
/s is delivered
to farm land. The surface runoff from the irrigated areas averages 0.7 m3
/s and the contribution
to ground water is 0.4 m3
/s. What is the water-conveyance efficiency? What is the water
application efficiency?
1 What substances occupy the pore space of a soil? Is the percentage pore space of a field
soil influenced by its water content?
Israelsen Q 4 pp 422
2 Are irrigated soils that are naturally well drained ever completely saturated? Explain.
3 Why are the actual heights to which water will rise by capillary action in a soil usually
less than the theoretical heights computed from Equation 7.5?

4 How can the concept of field capacity be determined and used even though there is no
point on the moisture drainage curve that uniquely defines field capacity?
5 Why is the moisture content at which a crop permanently wilts a function of
consumptive-use rate as well as soil texture?
6 What characteristics should be considered when deciding whether resistance blocks or
tensiometers should be used?
8 Describe the principle of operation of the neutron method of measuring soil moisture.
9 Are the texture and the structure of soils related to the salinity and alkali problems? If
so, explain.
10 Explain fully why lowering of the water table is helpful in the prevention of
accumulations of soluble salts on the surface of the soil.
11 Are studies of the consumptive use of water in irrigation likely to increase in importance
as time advances? Why?
12 List the three principal factors which influence time of irrigation and amount of water
to apply.
13 What are the essential points of difference between corrugations and furrows used for

irrigation?
14 What are the essential points of difference between corrugations and furrows used for
irrigations?
15 How do excessive intake rates interfere with good surface irrigation?
16 Explain how an irrigation stream too small to irrigate efficiently using surface methods
can often be applied very efficiently by sprinkler irrigation. Q18.3 Schwab pp 405

HOMEWORK
AE:201
SECOND YEAR
Q1 (a) What substances occupy the pore space of a soil? Is the percentage pore space
of a field soil influenced by its water content?
(b) A 12-hectare field is to be irrigated at a maximum rate of 1 cm/hr with a sprinkler
system. The root zone is 90 cm deep. The available moisture holding capacity of the soil is
16.5 cm/metre depth. The water application efficiency is 70 per cent. The field is to be irrigated
when 45 per cent of the available moisture capacity is depleted. The peak rate of moisture use
is 5 mm per day. Determine the net depth of application per irrigation, depth of water to be
pumped in centimetres, days to cover the field and the area irrigated per day.
Q2 (a) List the three principal factors which influence time of irrigation and amount of
water to apply.
(b) Determine the size of the irrigation stream required to irrigate an area of 15 hectares in
a region having no effective rainfall and where the peak consumptive use is 5 mm/day. The
irrigation system is operated for 13 hours each day. The field irrigation efficiency is 50 per
cent.
Q3 (a) What characteristics should be considered when deciding whether resistance
blocks or tensiometers should be used?
(b) A flow of 5 m3
/s is diverted from a river into a canal. Of this amount 4 m3
/s is delivered
to farm land. The surface runoff from the irrigated areas averages 0.7 m3
/s and the contribution
to ground water is 0.4 m3
/s. What is the water-conveyance efficiency? What is the water
application efficiency?
Q4 (a) Are irrigated soils that are naturally well drained ever completely saturated?

Explain.
(b) Compute the drain spacing for a clay loam soil having a drainable porosity of 0.06, a
hydraulic conductivity of 0.6m/day, and an imprervious layer 2.4 m below the drains. Drainage
requirements for the crop are such that the initial water table depth below the surface is 0.15
m, with a rate of drop of 0.21 m for the first day. Because of outlet depth, the maximum depth
of the drain is limited to 1.2 m measured to the bottom of the 125-mm drains.
HOMEWORK
AE:301
THIRD YEAR
HORTCULTURE STUDENTS
Q1 (a) Why is the moisture content at which a crop permanently wilts a function of
(b) A farmer having 10 hectares of land grows wheat in 5 hectares, potatoes in 2 hectares,
peas in 1 hectare and onions in 2 hectares during dry season. The irrigating season is 4 months.
The water requirements of wheat, potatoes, peas and onions are 45 cm, 50 cm, 15 cm and 10
cm, respectively. What size of irrigation stream will be required from a source which can
supply for 8 hours each day during the season?
Q2 (a) Describe the principle of operation of the neutron method of measuring soil
moisture.
(b) A 74-mm application of water measured at the pump increased the average water
, what is the water application efficiency?
Q3 (b) How can the concept of field capacity be determined and used even though there

is no point on the moisture drainage curve that uniquely defines field capacity?
(b) Furrow 100 m long and spaced 90 cm apart and having a slope of 0.2 per cen are
irrigated for 45 minutes by an initial stream of size equal to the maximum non-erosive stream.
The stream size is then reduced to half nad continued for 1 hour 20 minutes. Determine the
average depth of irrigation.
Q4 (a) Explain fully why lowering of the water table is helpful in the prevention of
accumulations of soluble salts on the surface of the soil.
(b) Determine the depth and spacing of drains to maintain a constant water table 1.5m
below the surface assuming that the height of the water table at the midplane is 0.5 m above
the centre of 150-mm drains. The average hydraulic conductivity of the soil is 0.6 m/day the
depth to the impervious layer is 3 m, and the excess irrigation rate is 3.0 mm/day per meter of
length. Assume a spacing of 40 m to select the equivalent depth.

TEST
JANUARY, 2000
HT:302
THIRD YEAR
Q1 (a) Describe what is meant by advance curve and a cut-back in a irrigation furrow
system.
(b) The following data was obtained from a test furrow in a sand soil
Stream size
(litres/min)
Distance
(m)
Advance
time
(min)
Wetted
perimete
r
(cm)
Furrow
cross-sectional
area
corresponding
to depth of flow
(cm2
)
100.00 30
50
70
2.00
6.75
12.00
25.39
25.82
26.39
60.00
93.00
103.00
Compute the accumulated infiltrated depth of the furrow.
Q2 (a) Explain briefly why sprinkler system of irrigation is preferred to surface
methods of irrigation.
(b) Determine the total pumping head for a sprinkler irrigation system on a level land. The
average operating pressure at the nozzle is 3kg/cm2
. The friction loss in the main is 6.5 m and
in the lateral is 4 m; the depth from the centre line of the pump to the water level is 5 m and
the required discharge is 31.6 L/s. The riser height is 1.5 m and friction loss in all valves 3.25

m. Determine the horsepower requirements of the pump if it operates at 65 % efficiency.
Q3 (a) List the three principal factors which influence time of irrigation and amount of
water to apply.
(b) Determine the size of the irrigation stream required to irrigate an area of 15 hectares in
a region having no effective rainfall and where the peak consumptive use is 5 mm/day. The
irrigation system is operated for 13 hours each day. The field irrigation efficiency is 50 per
cent.
iii)Readily available moisture.
(b) A stream of 135 litres per second was diverted from a canal and 100 litres per second
were delivered to the field. An area of 1.6 hectares was irrigated in 8 hours. The effective depth
of root zone was 1.8 m. The run off loss in the field was 432 m3
. The depth of water penetration
varied linearly from 1.8 m at the head end of the field to 1.2 m at the tail end. Available
moisture holding capacity of the soil is 200 mm/m depth of the soil. Determine the water
conveyance efficiency, water application efficiency, water storage efficiency and water
distribution efficiency, if irrigation was started at a moisture extraction level of 50 % of the
available moisture
TEST
JANUARY, 2000
AE:201
SECOND YEAR
Q1 (a) Why is the moisture content at which a crop permanently wilts a function of
(b) A farmer having 10 hectares of land grows wheat in 5 hectares, potatoes in 2 hectares,
peas in 1 hectare and onions in 2 hectares during dry season. The irrigating season is 4 months.
The water requirements of wheat, potatoes, peas and onions are 45 cm, 50 cm, 15 cm and 10
cm, respectively. What size of irrigation stream will be required from a source which can
supply for 8 hours each day during the season?

Q2 (a) What are the characteristic curves of a pump? Of what value are they?
(b) Determine the annual consumption of electrical energy by a motor driven centrifugal
pump installed in reservoir. The pump discharge 16 L/S against a total head of 7 m. The pump
efficiency is 70% and the motor efficiency is 84%. The drive efficiency may be assumed to be
100%. The pump is operated for 3500 hours per year.
Q3 (a) Explain the factors that have to be taken into consideration when designing a
furrow irrigation system.
(b) Furrows 90 m long and spaced at 75 cm apart are irrigated by an initial furrow stream
of 2 L/S. The initial furrow stream reached the lower end of the field in 50 minutes. The size
of the stream was the reduced to 0.5 L/S. The cut back stream continued for 1 hour. Estimate
the average depth of irrigation.
Q4 (a) i) Briefly explain how to measure the consumptive use of field crops
particular crop
(b)The root zone of a certain soil has a field capacity of 180 mm and a wilting point of 100
mm. The consumptive use of crops in July is 6 mm/day. Assuming no rainfall, how often
ought a farmer to irrigate? How much water should be applied at each irrigation if there is to
be no deep percolation?

SUPPLIMENTARY TEST
AE:201
SECOND YEAR
a)Consumptive use of a crop
b)Irrigation interval
c)Peak irrigation water requirement
(b) An experienced farmer in Majengo irrigation scheme in Mbeya region found out that
the average volumetric moisture content in the root zone depth of 1.20 mm will correspond
quite reasonably with moisture content at field capacity of 34%, two days after completing an
irrigation event. The daily consumptive use is 9 mm during the hottest month of the season.
During this period, what will be the average volumetric moisture content 10 days after
completing an irrigation event? If the management allowed deficit is 80 mm, what is the
required interval between irrigation events during the hottest month? What is the required
irrigation interval when the daily consumptive use is 6 mm?
Q 2.0 (a) Explain in detail the conditions that will allow you to use a centrifugal pump
and the problems you might encounter in the process of using it.
(b) A sprinkler irrigation system requires a centrifugal pump to operate. It was found out
that a small centrifugal pump with a discharge of 0.046 m3
/s could pump the irrigation water
at a head of 24 m if it is operating with an efficiency of 80 %. It was also found that at this
head, it requires 17.8 kW at 1400 rpm. Assuming the efficiency of the pump remains constant,
what is the theoretical discharge of the pump if its speed is increased to 2000 rpm? What is the

theoretical head and horsepower at 2000 rpm?
Q 3.0 (a) Explain the difference you would expect in root systems of crops which have
been irrigated by widely-spaced, heavy irrigations and frequent, light irrigations.
(b) Determine the water-applications efficiency and distribution uniformity if a stream of
100 L/s was delivered to the field for 2.5 hours, runoff averaged 55 L/s for 1 hour and depth of
penetration of the water varied from 1.8 m at the upper end to 1.2 m at the lower end of the
field. The root-zone depth is 1.8 m
Q 4.0 (a) How can the knowledge of the source of irrigation water be useful in solving a
drainage problem?
(b) An infrequent irrigation is practiced at the horticultural unit of the University whenever
oranges are irrigated. The soils at the orange farm are clay loam with a drainable porosity of
0.05, a hydraulic conductivity of 0.7m/day and an impervious layer 2.2 m below the drains.
Drainage requirements for the orange trees are such that the initial water table depth below the
surface is 0.20 m with a rate of drop of 0.25 m for the first day. Because of outlet depth, the
maximum depth of the drain is limited to 1.3 m measured to the bottom of the 125 mm drains.
Compute the drain spacing.

JUNE, 2000
EXAMINATION
AE:201
SECOND YEAR
Q1 (a) Briefly describe one method of operating a sprinkler system when the period
between irrigations is greater the the computed irrigatigation interval. (8 marks)
(b) An area of 10 ha is to be irrigated by a pumping system working for 10 hours a day.
The available moisture holding capacity of the soil is 160 mm/m and the root zone depth is 1.2
m. Irrigation is to be done when 50 % of the available moisture in the root zone is depleted.
Water application efficiency is 70%. Peak rate of moisture use by crops is 4 mm per day.
Losses in the water conveyance system are negligible.
Determine:
(i) The net depth of water application
(iii) The depth of water to be pumped per application and the required system's capacity (12
marks)
Q2 (a) Describe the principle of operation of the neutron method of measuring soil
moisture.(8 marks)
(b) A 74-mm application of water measured at the pump increased the average water
, what is the water application efficiency? (12 marks)

iii)Readily available moisture. (8 marks)
(b) A stream of 135 litres per second was diverted from a canal and 100 litres per second
were delivered to the field. An area of 1.6 hectares was irrigated in 8 hours. The effective depth
of root zone was 1.8 m. The run off loss in the field was 432 m3
. The depth of water penetration
varied linearly from 1.8 m at the head end of the field to 1.2 m at the tail end. Available
moisture holding capacity of the soil is 200 mm/m depth of the soil. Determine the water
conveyance efficiency, water application efficiency, water storage efficiency and water
distribution efficiency, if irrigation was started at a moisture extraction level of 50 % of the
available moisture. (12 marks)
JUNE, 2000
EXAMINATION
HT:302
THIRD YEAR
Q1. (a) How can knowledge of the source of irrigation water be useful in solving a
drainage problem? (8 marks)
(b) During an irrigation season 110 cm of irrigation and rain water was caught in rain gauge
located in a sprinkler irrigated field. The seasonal water requirement for the crop was estimated
to be 88 cm. Determine the depth of leaching and the leaching fraction. Neglect any changes
in soil water content that may have occurred during the irrigation season. (12 marks)
Q2. (a) Are the terms "Consumptive Use" and "evapotranspiration" the same? Explain.
( 8 marks )
(b) An area of vine plants has an average rooting depth of 1 m. The soil has a field capacity
of 0.32 by weight and a permanent wilting point of 0.14 by weight and a bulk density of 1.50.
A soil moisture sample weighed 60.13 gm and after oven drying 51.36 gm. What depth of
irrigation water should be applied to the root zone in order to replenish the soil moisture level
to field capacity? ( 12 marks )

Q3. (a) Under what conditions would you use a centrifugal pump? What are some of
the problems connected with its use? ( 8 marks )
(b) Farmers in the Lower Moshi irrigation scheme want to reclaim a water-logged area so
that they can grow beans instead of paddy. To reclaim the area, they need to buy a centrifugal
pump which can lift water at a rate of 100,000 L/hr against a total head of 30 m. Compute the
water horse power of the pump. If the pump has an efficiency of 80% what size of an engine
is required to operate the pump.
If a direct electric motor having an efficiency of 85% is used to operate the pump, compute the
cost of electrical energy in a month of 30 days. The pump is operated for 12 hours daily for 30
days. The cost of electrical energy is Tshs. 5,000/= per unit (kilowatt - hour). (12 marks)

IRRIGATION SYSTEMS AND DESIGN - IWRE 317 questions collection 1997 - 2018 (COURSE INSTRUCTOR: PROFESSOR A. K. TARIMO)

IRRIGATION SYSTEMS AND DESIGN - IWRE 317 questions collection 1997 - 2018 (COURSE INSTRUCTOR: PROFESSOR A. K. TARIMO)

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