EQ $1$ Estimate Potential Abstraction $($S$)$ S $=(1000/$CN$)-10$ CN $=$ average CN for watershed

EQ $2$ Calculate Runoff Q $($in$)$ Q $=($P $0\mathrm{.}2*$S$)2/($P $+0\mathrm{.}8*$S$)$ P $=$ Rainfall in inches

Note: Calculate the numerator and denominator separately, then divide.

$1)$ A contoured cornfield in good condition has a soil with a soil hydrologic group of B$.$ Use the SCS Runoff equation to estimate the runoff $($in inches$)$ from a $1\mathrm{.}5$ inch storm from it$.$

$2)$ a$)$ A watershed contains three land use$/$soil types:

a$.$ Forested, soil hydrologic group A $(1$ square mile$)$

b$.$ Low density urban $(1$ acre sized parcels$),$ soil hydrologic group B $(2$ square miles$)$

c$.$ Terraced row crops, soil hydrologic group C $(0\mathrm{.}5$ square miles$)$

Use this information to predict the total runoff $($in cubic feet$)$ from a $2$ year storm event $(2\mathrm{.}1$ inches of rainfall in $24$ hours$)?$

Step $1$: Use the CN tables to determine the curve number for each soil and landuse

a$.$ b$.$ c$.$

Step $2$: Compute the average CN for the watershed by multiplying each CN with its area, sum all together than divide the result by the total area of the watershed.

Step $3$: Compute Potential Abstraction $($S$)$ Use EQ$1$ above.

Step $4$: Compute the Runoff in inches using EQ$2$ above.

Step $5$: compute the area of the watershed in square feet $(3\mathrm{.}5$ square miles$)$

hint: $1$ square mile $=5286*5286$ ft$2$

Step $6$: Convert inches of runoff into cubic feet by converting the inches of runoff into feet of

water $($divide by $12)$ and multiplying by the watershed area in square feet