Method for inundation mappInE s55 5 + * + E*kEserseesserseere 31 4.2 Governing equation in MIKE paCKaỹ© - c Street 31 4.2.1 Rainfall runoff model (MIKE - Unit hydrograph model)
‘The results of maximum water level at nodes are along the rivers obtained from output of MIKE 11 and digital elevation map (DEM) with cell size 30 mx 30 m for land elevation was built based on topography of downstream in seales 1:10,000) are used for illustration the inundation maps by MIKE 11 GIS.
4.2 Governing equation in MIKE package
4.2.1 Rainfall runoff model (MIKE - Unit hydrograph model)
Rainfall runoff can be input in the MIKE 11 HD module as a point lateral discharge to ọ channel network SCS method of Unit hydrograph model was used to calculate rainfall runoff for sub basin.
The runoff curve number (also called acuve number or simply CN) is an empirieal parameter used in hydrology for predicting direct runoff or infiltration form rainfall excess (USDA, 1986) The curve number method was developed by the USDA Natural Resources Conservation Service, which was formerly called the Soil Conservation Service or SCS — the number is still popularly known as a
"SCS runoff curve umber" in the literature, The runoff curve number was developed from an empirical analysis of runoff from small catchments and hill slope plots monitored by the USDA It is widely used and isan efficient method for determining the approximate amount of direct runoff from a rainfall event in a particular area
‘The runoff curve number is based on the area's hydrologic soil group, land use, treatment and hydrologic condition References, such as from USDA indicate the runoff curve numbers for characteristic land cover descriptions and a hydrologic soil group.
Qis runoff ([L]: in) iis rainfall ((L); in)
Sis the potential maximum retention after runoff begins ((L in) is the initial abstraction ((L; in), or the amount of water before runoff, such as infiltration, or rainfall interception by vegetation; historically, it has generally been assumed that /, = 0.2, although more recent research has found that 1, 0.058 may be ọ more appropriate and accurate relationship (Hawkins, R.H; et al, 2002).
‘The runoff curve number CN, is then related
CN has a range from 30 to 100; lower numbers indicate low runoff potential while larger numbers are for increasing runoff potential The lower the curve number, the more permeable the soil is, As can be seen in the curve number equation, runoff cannot begin until the initial abstraction has been met.
Hydrodynamic model (MIKE 11 HD) eee eeeeeeeeeeeaee 33 4.2.3 Identification of inundation MAPS eeceeseeeteeesceeeteeeeeeeeeeeesneeeeeeees 34 4.3, Data USC mẽ
The model provides a choice between 3 different flow descriptions: dynamic wave approach, diffusive approach, and kinematic ware approach, In the research, the author used dynamic wave approach which solved the vertically integrated equations of conservation of continuity and momentum (the Saint-Venant equations) Thes