Example 1.1 Consider a reservoir with one inlet stream, one outlet at a dam and
ID: 114987 • Letter: E
Question
Example 1.1 Consider a reservoir with one inlet stream, one outlet at a dam and a surface area of 2.5 km2. There hasn't been any rain for weeks, and the reservoir level is falling at a rate of 3.0 mm/day. The average evaporation rate from the reservoir surface is 1.2 mm/day the inlet discharge is 10,000 m3/day, and the outlet discharge is 16,000 m3/day. Assuming that the only other important fluxes are the groundwater discharges in and out of the reservoir, what is the total net rate of groundwater discharge into the reservoir? 30 13Explanation / Answer
In this case,the reservoir is the region for which a balance is constructed.Fluxes in to this region include the inlet stream flow (I) and the net ground water discharge (G).fluxes out of this region include the outlet stream (O) and evaporation (E) from the surface.Hydrologic balance in this case requires
I+G-O-E=dV/dt
where dV/dtis the change in reservoir volume per time.calculate rate of change in reservoir volume as
dV/dt=-0.003m/day*2.5km2*(1000 m/km)2
=-7500m3/day
Similarly, the rate of evaporative loss is
E=0.0012m/day*2.5km2*(1000 m/km)2
=3000m3/day
Sloving the first equation for G yields a net groundwater discharge of 1500m3/day.
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