PLAN341 Lecture Notes - Lecture 6: Return Period, Stormwater, Drainage Density
20 Mar 2016
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Idf curves: amount and rate at which it falls are most important aspects of rainstorms, documented in idf curves which relate intensity of rainfall to the duration of occurrence for various probabilities, need data to design swm infrastructure. Landscape controls on overland flow: infiltration rate is dependant on the surface coverage and soil composition. Clay particles bind with water because they are charged and the void space is smaller between particles. Rational method: relates peak mischarge (q, m3/sec) to the drainage area (a, ha), the rainfall intensity (i, mm/hr) and the runoff coefficient (c) Sum the adjusted coefficients to get coefficients of runoff for the whole watershed: 5. Determine concentration time from graphs (fig 8. 4, 8. 5) and the velocity formula (manning"s equation, pg153; marsh 1997: 6. Select rainfall value for location and rainstorm desired. Use this value and concentration time to identify appropriate rainfall intensity from fig.
