5.1 IUH Relations

StandHyd is used mainly for urban areas. To obtain adequate results, the urban areas means the areas with impervious ratios larger than 20%. It is applicable for areas no larger than 200 hectares. For very large areas (> 200 hectares), calibration is required.

For rural areas, user can choose from NashHyd, ScsHyd and WilHyd. To obtain adequate results, the rural areas means the areas with impervious ratios lower than 20%. It is applicable for areas no larger than 200 hectares. For very large areas (> 200 hectares), calibration is required.

TYPE OF IUH	RELATION	*REMARKS
STANDARD		For Tp = DT (the computational time step) the STANDARD IUH becomes the URBHYD IUH from OTTHYMO 83.
NASH		N = Tp / k + 1 N is also the “number of reservoirs”
WILLIAMS		Calibration recommended. Where t_o is the inflection point after the peak; K_n is the storage coefficient of each reservoir; N is the number of reservoirs, and Γ(N) is the gamma function.
SCS	Is the NASH IUH with N = 5