(c) You have a one store catchment model that represents base flow, evapotranspi
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Question
(c) You have a one store catchment model that represents base flow, evapotranspiration and surface runoff due to infiltration excess. The following information is available. The initial soil water storage, S, (i.e. at the start of the day) is 130 mnm The soil water storage capacity, Smax, is 260 mm An intense rainfall event of 30 mm rainfall depth in 15 minutes occurs. This is the only rainfall during the day. The soil infiltration capacity is 40 mm/h. The potential evapotranspiration (PET) for the day is 4 mm. ·The actual evapotranspiration can be calculated as AET PET x S / Smar The base flow for the day is 4 mm. The catchment area is 200 km2 (i) Estimate the actual evapotranspiration for the day (ii) Estimate the surface runoff depth for the day. (iii) Estimate the total runoff volume for the day. (1 mark) (2 marks) (2 marks) iv) Estimate the soil water storage at the end of the day. (3 marks)Explanation / Answer
1. AET = PET* S/SMAX = 4*130/260 = 520/260 = 2
2. THE FORMULA IS( INTENSE RAINFALL EVENT-INITIAL STOARGE OF DAY)2/(INTENSE RAINFALL EVENT-INITIAL STOARGE OF DAY) +SOIL FILTERATION CAPACITY SO THE EQUATION IS (30MM-130MM)2/(30-130)+40 = 10000/60 = 166.66MM/HR.
3. CONSIDER THE ABOVE QUESTION ASKED i.eSURFACE RUNOFF DEPTH BE Q. SO TOTAL RUNOFF OF DAY = Q*CATCHMENT AREA = 166.66*200 =33333.33KM2.
4. SOIL WATER STORAGE = BASE FLOW OF THE DAY*SOIL WATER STORAGE CAPACITY =4*130=520MM2
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