Question

Consider a drainage basin having 60% soil group A and 40% soil group B. Five years ago the land use pattern in the basin was ½ wooded area with poor cover and ½ cultivated land (row crops/contoured and terraces) with good conservation treatment. Now the land use has been changed to 1/3 wooded area with poor cover, 1/3 cultivated land (row crops/contoured and terraces) with good conservation treatment, and 1/3 commercial and business area.
(a) Estimate the increased runoff volume during the dormant season due to the land use change over the past 5-year period for a storm of 35 cm total depth under the dry antecedent moisture condition (AMC I). This storm depth corresponds to a duration of 6-hr and 100-year return period. The total 5-day antecedent rainfall amount is 30 mm. (Note: 1 in = 25.4 mm.)
(b) Under the present watershed land use pattern, find the effective rainfall hyetograph (in cm/hr) for the following storm event using SCS method under the dry antecedent moisture condition (AMC I).

Answer 1

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