430.4 m 430.4 m Q4) The table below gives the monthly inflows during a criical l

ID: 1730223 • Letter: 4

Question

430.4 m 430.4 m Q4) The table below gives the monthly inflows during a criical low water period at a site of a /, ·, proposed dam. It is planned to construct a concrete dam at the site to create a reservoir. Downstream water rights require a release of 5.4 hectare-meter per three months. Assume that 57% ofthe rainfall on the land area to beflo ded by the reservoir has reached the stream in the past. Using a net increased pool area of 405 hectares, find the required useful storage. [15 Marks] Take pan evaporation coefficient equal to 0.76 Pan DeaMonth a-m Month Inlow Precipitat., Inflow Precipitat.,Evaporat, ha-m Inflow Precipitat., Evaporat., ha-m Evaporat, Demand, 15.0 20 33.7 5412.5 73 27 20 86 7.5 f a reservoir was terminated when 20% of its initio cd life o l cana ein

Explanation / Answer

Prepare a table with cumulative inflow, demand, precipitation, evaporation and downstream water discharge for 3 months at a time.

Precipitation in ha-m=Precipitation in mm*Area * 10-3

Precipitation reach the stream=Ps=0.57*Precipitation in ha-m

Evaporation in ha-m=Es=Evaporation in mm*Area *pan cofficiesnt* 10-3

Adjusted inflow=Inflow+Ps-Es-downstream discharge

Storage required=Adjusted inflow-Demand

Month

Inflow (ha-m)

Demand (ha-m)

Precipitation (mm)

Pan evaporation (mm)

Ps (ha-m)

Es (ha-m)

Downstream Discharge(ha-m)

Adjusted Inflow(ha-m)

Storage required (ha-m)

(1-3)

4.2

120

289

27.702

88.954

5.4

-62.4522

-104.4522

(4-6)

149.5

23.701

5.4

120.3994

100.3994

(7-9)

323.7

104

32.011

5.4

286.2888

244.2888

(10-12)

11.8

298

271

68.793

83.414

5.4

-8.2205

-32.2205

?Storage=

208.031

Hence total useful storage required=208.031 ha-m