one more water budget problem

willowthewisp

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Joined
Aug 25, 2013
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Hello all. I posted a water budget problem last evening and I got some much needed help. I have one more, this ones seems more complicated to me, that I am having a hard time understanding:

"There is a desert landscape around a sea. the entire area is 1500 km2 including the area of the sea which is 810 km2. Annual precipitation in the entire area is 15 mm, of which 20% infiltrates to the groundwater. Evaporation is high, with 85% derived from surface evaporation and the remaining 15% is evaporation from the water table though the sand. Annual transpiration only totals 2 mm/yr all of which is surface transpiration. Water flows in from a river at a rate of 5 m3/sec and is controlled to maintain a volume in the sea (no other surface water input or output exists). Assume a steady-state conditions with respect to the groundwater system (ex: Gin = G out, Sg = 0). Solve for Qg (and interpret the net direction of flow), Es and Eg."

I need to find Qg in cm/yr and Es and Eg in mm/yr.

I am meant to use the groundwater equation which is: change in Sg = I + Gin - Gout - Qg - Eg - Tg. Where Sg is change in groundwater, I is infiltration, Gin is groundwater inflow, Gout is groundwater outflow, Qg is groundwater to stream, Eg is groundwater evaporation and Tg is groundwater transpiration.

But since I also need to solve for Es which isn't in the groundwater equation, I figure I need to use the surface water equation at some point which is: change in Ss = P + Qin + Qg - Qout - Es -Ts - I. Where P is precipitation, Qin is stream inflow, Qg is groundwater to stream, Qout is stream outflow, Es is surface evaporation, Ts is surface transpiration and I is infiltration.

I'm not really too sure where to start with this problem. The only things I have been able to work out are the infiltration rate is 3 mm/yr, Tg is zero since all the transpiration is surface and not groundwater. and I'm thinking Gin and Gout will cancel each other out since this problem is assumed to be a steady state.

Thanks for any help.
 
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