A catchment having an area of 150 km2has the ø index 0.3 cm/hr....
Total depth of rainfall = 1 cm = 0.01 m
Total runoff volume = Area of hydrograph = 1/2 x time base x peak ordinate
0.01 x 150 x 106 = 0.5 x ( 20 x 3600) x peak ordinate
Peak ordinate = 41.66
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A catchment having an area of 150 km2has the ø index 0.3 cm/hr....
Following characteristics:
- Average annual rainfall: 1000 mm
- Runoff coefficient: 0.4
- Average slope: 5%
- Average soil infiltration rate: 10 mm/hour
Using this information, we can calculate the various components of the water balance for the catchment:
1. Precipitation: The total amount of rainfall that falls on the catchment in one year can be calculated as follows:
Precipitation = Area x Rainfall = 150 km2 x 1000 mm = 150,000,000 m3
2. Effective rainfall: This is the portion of the rainfall that contributes to runoff. We can calculate this as follows:
Effective rainfall = Precipitation x Runoff coefficient = 150,000,000 m3 x 0.4 = 60,000,000 m3
3. Runoff: This is the amount of water that flows out of the catchment. We can calculate this as follows:
Runoff = Effective rainfall = 60,000,000 m3
4. Infiltration: This is the amount of water that is absorbed by the soil. We can calculate this as follows:
Infiltration = Effective rainfall x (1 - Runoff coefficient) = 60,000,000 m3 x (1 - 0.4) = 36,000,000 m3
5. Evapotranspiration: This is the amount of water that is lost through evaporation and plant transpiration. We don't have enough information to calculate this directly, but we can estimate it using the water balance equation:
Precipitation = Runoff + Infiltration + Evapotranspiration
Rearranging this equation, we get:
Evapotranspiration = Precipitation - Runoff - Infiltration = 150,000,000 m3 - 60,000,000 m3 - 36,000,000 m3 = 54,000,000 m3
6. Groundwater recharge: This is the amount of water that infiltrates into the ground and recharges the groundwater system. We don't have enough information to calculate this directly, but we can estimate it using the water balance equation:
Groundwater recharge = Infiltration - Evapotranspiration
Substituting our calculated values, we get:
Groundwater recharge = 36,000,000 m3 - 54,000,000 m3 = -18,000,000 m3
This negative value indicates that the groundwater system is being depleted rather than recharged. However, we should note that our estimates of evapotranspiration and groundwater recharge are quite rough, so this result should be taken with some caution.