How is CN number calculated?

How is CN number calculated?

The weighted CN is calculated by taking the sum of each CN value multiplied by its fraction of the total subcatchment area. The sum is (usually) rounded to the nearest whole number, as described below.

How is hydrology calculated?

Use the Rational Equation for Peak Flow Calcuation:

1. Q = Cw * i * At. Q =
2. 100-Year Pre-Development Rainfall Peak Flow. Cw =
3. Qpost-100year= 0.43 * 2.5 * 10.89 =
4. 100-Year Post-Development Rainfall Peak Flow. Cw =
5. Qpost-100year= 0.49 * 2.5 * 10.89 =
6. 13.21 cfs.

How do you calculate potential maximum retention?

The Potential Maximum Retention in terms of Curve Number mainly represents infiltration occurring after runoff has started is calculated using Potential Maximum Retention = 254*(100/Curve Number-1). To calculate Potential Maximum Retention in terms of Curve Number, you need Curve Number (CN).

What is the full form of SCS CN *?

Abstract. This paper revisits the popular rainfall-runoff Soil Conservation Service Curve Number (SCS-CN) methodology in perspective of Strange (1892),1 rainfall-runoff procedure widely used in Southern parts of India.

What is a SCS Curve Number?

SCS curve numbers are used to estimate the amount of precipitation which becomes runoff, and the amount which infiltrates into the soil.

What is AMC in hydrology?

The Soil Conservation Service curve number (CN) method commonly uses three discrete levels of soil antecedent moisture condition (AMC), defined by the 5-day antecedent rainfall depth, to describe soil moisture prior to a runoff event.

What is the rainfall excess?

One of the processes that can generate surface runoff is rainfall excess, which is a process controlled at the surface of the soil. This occurs when rainfall reaches the soil at a rate in excess of the soil’s ability to absorb, which is called infiltrability.

How do you calculate phi index in hydrology?

ϕ∆t = (1.6-0.72)/13 = 0.068 inch or ϕ = 0.068 * (60/15) = 0.272 inch/hr. Plotting of a line corresponding to 0.068 on the rainfall hyetograph shows that the assumption of M = 13 is correct because we end up with 13 ordinates in the excess rainfall hyetograph.

How is curve number related to potential maximum retentions?

Equation 4.5 is the rainfall-runoff relationship used in the Curve Number Method. It allows the runoff depth to be estimated from rainfall depth, given the value of the potential maximum retention S. This potential maximum retention mainly represents infiltration occurring after runoff has started.

What is SCS CN model?

The SCS-CN method is one of the most popular methods for computing the volume of direct surface runoff for a given rainfall event. On one hand, SCS model is an empirical model and it just needs a single parameter-Curve Number which lumps together the hydrological impacts of land use.

What is the curve number of water?

The runoff curve number (also called a curve number or simply CN) is an empirical parameter used in hydrology for predicting direct runoff or infiltration from rainfall excess.

What is antecedent moisture content?

Antecedent moisture is the relative wetness or dryness of a sewershed, which changes continuously and can have a very significant effect on the flow responses in these systems during wet weather. Antecedent moisture conditions are high when there has been a lot of recent rainfall and the ground is moist.

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