Homework help

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.

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