Lab 13 - Predicting Discharge and Soil Erosion

• Estimating Runoff Depth using the Curve Number method – Land use or cover type– Hydrologic condition– Soil type

• Estimating Peak Runoff– A function of the Time of Concentration, Tc– The faster the runoff time => the bigger the peak

• Estimating Erosion Losses using the Universal Soil Loss Equation– Precipitation– Topography– Soils– Land use or land cover– Treatment or conservation practices

Curve Number Method

Peak Discharge

• Qp = Up · A · Q– Qp is peak runoff (L/s)– Up is unit peak (L/s/ha/mm)

• a function of Tc• Tc is the time of concentration, or the time for water to runoff

of the watershed• the faster the runoff time, the bigger the peak

– A is watershed area (ha)– Q is runoff depth (mm)

• From the curve number method

Universal Soil Loss Equation

• A = R · K · LS · C · P– A is soil loss in tons per acre per year– R is rainfall erosivity factor– K is soil erodibility factor– LS is length-slope (topographic) factor– C is the land use or land cover factor– P is the treatment or conservation practices factor

Rainfall Erosivity Factor