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All Topics | Topic "Irrigation Demands Only vs Rainfall Runoff"
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Author Message
Eng. Rodrigo Urquiza

Subject: Irrigation Demands Only vs Rainfall Runoff   
Posted: 6/5/2021 Viewed: 76 times
Hello! I´ve got a question about the runoff generated from precipitation in catchments modeled with these two options.
I've made a little WEAP model to prove the differences, there's one irrigation demands only catchment and a rainfall runoff one, both with a transmission link from a river and runoff/infiltration link back to it. I gave them 100 ha. area with 20mm/month ETref, Kc=1, irrigation fraction=0.5, and 10 mm/month precipitation with 80% effective precipitation.
When I check results turns out that water demand is the same for both as expected (20mm/month - 0.8 * 10mm/month)/0.5)*100ha= 24000 m3. But the water that returns to the river is different, it's 14000 m3 for the rainfall runoff and 12000 m3 for the irrigation only. I know that 12000 m3 comes from the water not used by crops because of irrigation fraction (24000 m3/ 0.5), and the additional 2000 m3 in the rainfall runoff comes from the fraction of not effective precipitation (0.20 * 10mm).
Now my question is what happens to those 2000 m3 in the irrigation demands only catchment, if it goes out of the model or where does it goes?
Thanks for the help.
Rodrigo Urquiza
Topic "Irrigation Demands Only vs Rainfall Runoff"