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The catchment area of city is 500 hectares. Assuming that surface on which rainfalls is classified as follows : :
S.NO Types of surface % area C 1 Forest and wooden area 10 0.15 2 open ground + unpaved street 10 0.20 3 parks + lawns + gardens 15 0.15 4 Gravel roads 20 0.25 5 Asphalt pavements 20 0.85 6 Water tight roof surfaces 25 0.9
Calculate run off coefficient of area. Also calculate storm water, if area to be served is 500 hectares, time of entry is 15 minutes and time of flow is 10 minutes.
[Ans: `0.5025`, `15.32 m^3/s`]
The catchment area of city is 500 hectares. Assuming that surface on which rainfalls is classified as follows : :
| S.NO | Types of surface | % area | C |
| 1 | Forest and wooden area | 10 | 0.15 |
| 2 | open ground + unpaved street | 10 | 0.20 |
| 3 | parks + lawns + gardens | 15 | 0.15 |
| 4 | Gravel roads | 20 | 0.25 |
| 5 | Asphalt pavements | 20 | 0.85 |
| 6 | Water tight roof surfaces | 25 | 0.9 |
Calculate run off coefficient of area. Also calculate storm water, if area to be served is 500 hectares, time of entry is 15 minutes and time of flow is 10 minutes.
[Ans: `0.5025`, `15.32 m^3/s`]
Solution:
Average runoff coefficient is given by,
`C=(C_1A_1+C_2A_2+C_3A_3+C_4A_4+C_5A_5+C_6A_6)/(A_1+A_2+A_3+A_4+A_5+A_6)`
`=(0.15**0.1+0.20**0.1+0.15**0.15+0.25**0.20+0.85**0.20+0.9**0.25)/1`
`=0.5025`
Now,
Time of concentration is,
`t=15+10=25\ mi n`
Now,
Storm water flow rate is,
`Q=(CiA)/360`
where,
`i=1020/(25+20)=22.67` mm/hr
Thus,
`Q=(0.5025**22.67**500)/360`
`=15.82 m^3/s`
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Similar Question
The surface of the town on which the rainfalls is classified as follows :
| Types of surface | % area | Runoff coefficient |
| Roof | 25 | 0.8 |
| Pavements and yards | 25 | 0.85 |
| Macadamized roads | 15 | 0.32 |
| Gravel roads | 10 | 0.2 |
| Unpaved streets | 20 | 0.15 |
| Lawns and gardens | 5 | 0.2 |
What is the runoff of the catchment if,
- Total area of catchment is 12 hectares
- Time of concentration for the area is 15 minutes.
The catchment area of city is 500 hectares. Assuming that surface on which rainfalls is classified as follows : :
| S.NO | Types of surface | % area | C |
| 1 | Forest and wooden area | 10 | 0.15 |
| 2 | open ground + unpaved street | 10 | 0.20 |
| 3 | parks + lawns + gardens | 15 | 0.15 |
| 4 | Gravel roads | 20 | 0.25 |
| 5 | Asphalt pavements | 20 | 0.85 |
| 6 | Water tight roof surfaces | 25 | 0.9 |
Calculate run off coefficient of area. Also calculate storm water, if area to be served is 500 hectares, time of entry is 15 minutes and time of flow is 10 minutes.
[Ans: `0.5025`, `15.32 m^3/s`]
Determine the quantity of sewage in `m^3`/sec for the combined system from the following data :
- `50 %` of the area is roofs and pavements (`C_1 = 0.8`)
- `50 %` of the area is vacant plots (`C_2 =0.1`)
- Area of the community ` 5` hectares
- Population density = `700` persons/hectare
- Water supply rate = `150` lpcd.
- Peak factor = `3`
- Time of concentration =`10` minutes.