Quick Answer
Soil types play a crucial role in runoff calculations as they affect the rate and volume of water infiltration, which in turn determines the amount of water available for collection in a cistern. Different soil types have varying infiltration rates, with sand having the highest rate and clay the lowest. This characteristic is essential in designing a cistern that can effectively collect and store rainwater.
Understanding Soil Infiltration Rates
Soil infiltration rates vary significantly depending on the soil type. For instance, sand has an infiltration rate of around 1-2 inches per hour, while clay has an infiltration rate of around 0.01-0.1 inches per hour. This means that for a 1-inch rainfall event, sand can infiltrate approximately 1-2 inches of water, whereas clay can only infiltrate about 0.01-0.1 inches. Understanding these rates is crucial in sizing a cistern to effectively collect rainwater and minimize runoff.
Applying Soil Infiltration Rates to Cistern Design
When designing a cistern, it’s essential to consider the soil infiltration rates in the catchment area. This can be achieved by using the “curve number” method, which takes into account the soil type and other factors such as land use and slope. For example, if the soil type is clay and the curve number is 95, the rainfall-runoff coefficient (C) would be around 0.95. This value can then be used to estimate the amount of runoff from the catchment area, which in turn determines the required cistern size.
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