18 Flood may be measurable as to height, area inundated, peak discharge, and
volume of flow. The height of a flood is of interest to those planning of build structure along or across streams; the area inundated is of interest to those
planning to occupying in any manner the floodplains adjacent to a streams; the peak discharge is of interest to those designing spillways, bridges, culverts, and
flood channel; and the volume of flow is interest to those designing storage works for irrigation, water supply, and flood control.
Floodplains are areas with ecologically important wetlands, and mainly exhibit competitive advantages for human urban. Resolving the potential conflict
between ecological value and human use is consequently a major issue in determining the most appropriate flood hazard management strategy.
2.3.2 Flood Routing
Flood routing defined as the procedure whereby the time and magnitude of a flood wave at a point on a stream is determined from the known or assumed data
at one or more points upstream. The movement of a flood wave down a channel or through a reservoir and
the associated change in timing or attenuation of the wave constitute an important topic in floodplain hydrology. It is essential to understand the theoretical and
practical aspects of flood routing to predict the temporal and spatial variations of a flood wave through a river reach or reservoir. Flood routing methods can also be
used to predict the outflow hydrograph from watershed subjected to a known amount of precipitation.
19 Routing technique may be classified into two major categories: simple
hydrologic routing and more complex hydraulic routing. Hydrologic routing involves the balancing of inflow, outflow and the volume of storage through use
of the continuity equation. Hydrologic routing can be used in flood prediction, flood control measures, reservoir design and operation, watershed simulation, and
urban design. Whereas hydraulic routing method is based on the solution of the continuity equation and the momentum equation for unsteady flow in open
channel. Hydraulic routing method is used in case: upstream movement of tides and storm surge, backwater effect from downstream reservoir and tributary
inflows, flood waves in channels of very flat slope, and abrupt wave caused by sudden releases from reservoir or dam failure.
Figure 4. Flood in Jakarta
20
2.3.3 Flood Modeling
The first step in risk management for floods is the flood hazard mapping. For planning and evacuation procedures, the demand for flood information and
digitals maps of predicted extent and risk of flooding has been increased. To produce these maps Geographical Information System GIS, Remote Sensing
RS and flood modeling is very useful. Simulation and modeling of flood are a rapidly developing field in
hydrology. The flood simulation and model results are a good way of providing relevant information on how the flood is going to behave at the location where
people live and how the flood will affect them. There are many types of flood models, 1-dimensional 1D floods models
such as manning equation, HEC-2, and dynamic one-dimensional model such as SOBEK, MIKE-11 have been used to estimate the possible flood using time series
of river discharge. 1-D model has some limitation on include all details in modeling and it is very difficult to simulate local conditions on a small scale
accurately Singh, 1995 Two dimensional 2D modeling based on the raster grids for terrain
description, surface roughness coefficients and hydrological data water level, discharge and cross section provide information to generate flood hazard maps.
Over the past ten years significant advances have been made in integrating 1D and 2D models resulting in hydrodynamic model of floodplains and integrated
1D channel flow and 2D overland flow. The idea of integrating 1D hydrodynamic modeling technologies, Digital Elevation Model DEM and GIS
system is to take advantage of the best combination of 1D and 2D and presenting
21 them in the GIS as maps. Benefit of the integration of GIS, RS, 2D flood
modeling is to provide information for users such as land use planning, evacuation planning and environmental impact assessment.
2.3.4 Step in Hydrology Modeling Development
