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In order to apply the hydraulic model, energy or continuity and momentum equations should be solved numerically for the calculated area. This solution process requires Manning's roughness coefficients which are decided upon land use types. These empirical roughness coefficients are a vital determinant of connecting land and flood analysis. The coefficients were drawn from the available literature (Liu et al. 1998; Guo et al. 2010) and are summarized in Table 1. It is seen that these coefficients range from 0.016 to 0.15 with a difference of more than eight times with the greatest for forest and the smallest for urban area. Each grid cell was assigned a Manning's roughness coefficient dependent on its land use/cover type.

Table 1

Manning's roughness coefficients corresponding to land use/cover (summarized from Guo et al. (2010) and Liu et al. (1998))

Land use/coverManning's roughness coefficient
Urban land (incl. rural road, town land, rural residence and mining land, highway) 0.016 
Bare land (incl. saline alkali land, swamp, sand land, bare rock, construction site and threshing ground) 0.025 
Water surface (incl. river, lake, reservoir, aquaculture) 0.027 
Grassland (incl. reed and mudflat) 0.030 
Cultivated land (incl. pasture, irrigation and water conservancy works, ridge, confined feeding operations and green house) 0.035 
Heavy brush 0.075 
Forest 0.150 
Land use/coverManning's roughness coefficient
Urban land (incl. rural road, town land, rural residence and mining land, highway) 0.016 
Bare land (incl. saline alkali land, swamp, sand land, bare rock, construction site and threshing ground) 0.025 
Water surface (incl. river, lake, reservoir, aquaculture) 0.027 
Grassland (incl. reed and mudflat) 0.030 
Cultivated land (incl. pasture, irrigation and water conservancy works, ridge, confined feeding operations and green house) 0.035 
Heavy brush 0.075 
Forest 0.150 

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