DSİ Cowan Calculator

Estimate Manning's roughness coefficient (n).

Cowan's Method for Roughness

The Cowan Method is a systematic approach used to estimate the Manning's roughness coefficient (n) for natural streams, floodplains, and excavated channels. It is widely recommended by institutions like DSİ (State Hydraulics Works in Turkey).

Formula: n = (n0 + n1 + n2 + n3 + n4) × m5

n0: Base material of the channel
n1: Degree of surface irregularity
n2: Variations in shape and size of the channel cross section
n3: Relative effect of obstructions
n4: Effect of vegetation
m5: Correction factor for meandering of the channel

Using this step-by-step methodology ensures a more accurate calibration of hydraulic models compared to guessing an overall base friction value.

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Base Material (n0)

Irregularity (n1)

Cross Section Variation (n2)

Obstructions (n3)

Vegetation (n4)

Meandering (m5)

Manning's n Value

0.000

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