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# 02-05 - Announcement Lecture notes will be posted on...

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Announcement • Lecture notes will be posted on Blackboard after class.

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Examples on the International Level Ex. Build up of T.D.S. in U.S. rivers because of irrigation return flow. Here's what happens: First apply water to field to grow crops: Result: Salt concentration build-up in soil to some level such that amount leaving in return flow equals the amount coming in, in the irrigation water. Flow =Qi, TDS = Ci Flow = Qp Flow = Qv Flow = Qs; TDS = Cs Cs > Ci net water loss due to evapotraspiration (assume: no salt input or loss via atmosphere) return flow underdrain or subsoil soil field irrigation H 2 O evaporation precipitation plants Qv > Qp
@ Steady State: Salt input = salt output Formulate an expression for the mass rate of salt input & output: salt input: salt output: @ steady state: So, at steady state, the salt concentration in the soil = constant Units = mass/time ; Ci (mg/L) x Qi (L/day) Qs Cs Qs Cs = Qi Ci so: Qs/Qi = Ci/Cs

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Example: assume Ci = 210 mg/L (a good irrigation water) If the maximum salt concentration plants can stand is 2100 mg/L (above this level plants die because of osmotic problems) How much (%) of the water applied must be used to carry off excess salt? What if Ci = 700 ppm (still Class I irrigation water in Calif.)? Qs/Qi = 700 / 2100 = 0.33 [33% !] Qs/Qi = Ci / Cs = 210 / 2100 = 0.1 [10%]
Typical result for deterioration of water quality in a stream receiving irrigation return flow: 10 cfs (i.e. 33%) 2100 ppm (max. that will allow crops to grow) 70 + 10 = 80 cfs 875 ppm

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02-05 - Announcement Lecture notes will be posted on...

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