Problem2 You are commissioned to evaluate a Rapid Infiltrati

Problem-2. You are commissioned to evaluate a Rapid Infiltration Basin (RIB) for a local municipality, the owner (the municipality) has provided you with the following information: Basin will be confined by vertical walls and at least 1-m deep The average rate of infiltration is Ri 12-cm/year Local average precipitation P-4-in/year Average flowrate in facility Q = 0.044-MGD (Million Gallons per Day) You consulted the local university to determine the measured average evaporation rate. The standard evaporation rate in the Las Vegas Valley is 190-cm/year, the standard value for large open bodies of water is 20% larger, 228-cm/year. [These are actual recommended values for design in the Las Vegas Valley, keep note of them for future reference]. Calculate: Perform all the following calculations (a, b and c) for both evaporation rates 190 cm/year as well as 228-cm/year and compare results. a) Minimum required basin area for the above data. Size the basin as a circle as well as a square. b) Minimum required basin area assuming a soil with greater than 10% fines. c) Determine the infiltration rate Ri if the RIB is 500-ft x 728-ft for E-190-cm/year and 500-ft x 600-ft E-228-cm/year. Please answer a,b and c

Solution

Average flowrate in the facility= 0.044 MGD = 0.044 X 1000000 X 0.00378541 cubic metres per day = 166.55804 cu.m per day

Average infiltration rate = 12 cms per year = 12/365 = 0.033 cms per day or 0.00033 mtr per day (considering 365 days in a year)

Assuming a minimum area of \'A\' square metres of the infiltration basin with 1 mtr depth and consideing the evaporation rate of 190 cms/yr or 190/365 cms/day or 0.0052 mtrs per day;

166.558 - 0.0052 X A = 0.00033 X A

or, 166.558 = 0.00553 X A

or, A = 30118.99 square metres

Assuming the basin is rectangular, the area can be considered as 210 X 150 square metres whereas considering the circular shape, the basin will be of radius 100 metres. This will be the minimum area.

Now, Assuming a minimum area of \'A\' square metres of the infiltration basin with 1 mtr depth and considering the evaporation rate of 228 cms/yr or 228/365 cms/day or 0.00625 mtrs per day;

166.558 - 0.00625 X A = 0.00033 X A

or, 166.558 = 0.00658 X A

or, A = 25312.77 square metres

Assuming the basin is rectangular, the area can be considered as 200 X 130 square metres whereas considering the circular shape, the basin will be of radius 90 metres. This will be the minimum area.

When RIB is 500 ft x 728 ft or 152.4 mtrs x 221.9 mtrs and evaporation rate = 190 cms/yr

RIB Area = 33817.56 square metres

Infilration rate x 33817.56 = 166.558 - 0.0052 x 33817.56

Infiltration rate = 0.000274 mtrs per day 0.0274 cms per day or 10.001 cms per year

When RIB is 500 ft x 600 ft or 152.4 mtrs x 182.88 mtrs and evaporation rate = 228 cms/yr

RIB Area = 27870.912 square metres

Infilration rate x 27870.912 = 166.558 - 0.00625 x 27870.912

Infiltration rate = 0.0002739 mtrs per day 0.02739 cms per day or 9.997 cms per year