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Q1 Determine the water balance for a given the data below in a rural catchment where an earth dam of surface area when full is 870 m2.
Human population data
Human population in 2007 = 5900
No of households in 2012 = 1150
Human water consumption = 20 litres / per person – day
The longest duration of dry spell = 120 days
Rate of population growth = 2.4%
60% of population draw water from the dam daily
Livestock data
Grade cow consumes 50 litres/head-day
Indigenous cow consumes 30% of grade cow consumption
Cattle ownership composition (Grade to indigenous cow) = 1:4
Assume sheep and goats have negligible impact
Average No of livestock per household = 12
Assume 50% of households own livestock
Irrigation data
ETo = 4 mm/day
Kc values for different stages: Germination = 0.6, Flowing=0.8, Fruiting=1.0, Maturity = 0.9
Crop duration = 120 days
Irrigation hours per day = 4 hours
Irrigation days per week = 5 days
Irrigation efficiency = 50%
Area to be irrigated at any one time = 25 ha
Crop growth rate = 1 annually
Hydrology
Runoff coefficient = 10%
Catchment area 2.5 km2
Mean annual rainfall = 900 mm
Open water evaporation = 1700 mm/yr
Q2 Given the dimensions of an earth dam as stated below
Upstream length = 20 m
Downstream length = 15 m
Upstream slope = 1:4
Downstream slope = 1:3
Height of embankment = 6 m which is the maximum water level for the worst case scenario
Width of dam = 5 m
Dry density of construction material = 1850 kg/m3
Gravitational acceleration =9.81 m/s2
Determine the forces acting on the dam in KN/M length
Q3. For the dam in Q2, determine its safety against overturning and sliding assuming the factor of safety is 1.5.
