Effect of water surface slope and friction slope on the value of the estimated Manning’s roughness coefficient in gravel-bed streams

Abstract The aim of the study was to assess possibility using empirical formulas determine roughness coefficient in gravel-bed streams, bed slopes which range from 0.006 0.047. Another impact taking into account conditions non-uniform flow on application these and develop correlation relationships between water surface slope also friction order estimate n streams. studies were conducted eight measuring sections streams located Kraków-Częstochowa Upland, southern Poland. 0 for calculated transformed Bernoulli equation based results surveys hydrometric measurements. values compared with calculation obtained fourteen presenting as a function slope. Lacey, Riggs, Bray Sauer found provide an approximate value, while best estimation Riggs formula. It that instead or did not improve estimated tested formulas. shown lack differences RMSE MAE error developed equations indicate no influence assumed value coefficient.