Atreatment plant with a capacity of 20 mgd (million gallons per day) has a normal daily flow equal to 60 percent of capacity. when it rains the flow increases by 30 percent of the normal flow. what is the flow on a rainy day?

rea of watershed is 220 km2

Annual precipitation in the watershed area is 4.2*109

Equivalent depth is

4.2*109/ 220*106 = 19.1 m

This is approximately an order of magnitude too high

11)

(1)

River Storage= 12 * 106 m3

River Inflow = 14 m3/s

River Outflow – 20 m3/s

After 4 hours

Inflow = 18 m3/s

Outflow = 26 m3/s

Average groundwater flow TO river during these fours hours = 9 m3/s

Assuming a linear increase, we average the inflow as:

14 + 18 = 16 m3/s

2

However, this is not the only source of water, since there is also groundwater inflow.

The total flow of water is

16 + 9 = 25 m3/s

The average river outflow can be calculated the same way

20 + 26 = 23 m3/s

2

The change in storage is therefore the difference between inflow and outflow over a 4 hour period:

Inflow- Outflow = Change in Storage

       - 23 = 2 m3/s over a 4 hour period

4 hours = 240 minutes = 14,400 seconds

Storage = 2 m3/s * 14,400 = 28,800 m3

(2) Since the river storage at the beginning of the four hour period was 12* 106 m3

and we added 2.22*104 m3, the new storage volume is 1202.8*104 m3.

15)

Surface Area of lake = 14 km2 = 14 * 106 m2

Average inflow rate into lake = 50 m3/s

Average ouflow rate = 25 m3/s

Lake storage increases in 1 day with 14.7 cm

In other units:

Inflow = 50 m3/s * 86400 s/day = 4.32 * 10 6 m3/day

Outflow = 25 m3/s * 86400 s/day = 2.16 * 10 6 m3/day

Storage = 14.7 cm * area of lake = 0.147 m * 14 * 106 m2 = 2.058* 106 m3/day

Writing water balance

Evaporation = Inflow – Outflow – Lake volume change

Evap = 4.32*106 m3/day – 2.16*106 m3/day – 2.058*106 m3/day

Evap = 1.02 * 105 m3/day

Over lake of area 14 * 10 m2, equivalent depth of :

1.02*105 m3/day = 7.3 mm/day

14 * 106 m2

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