Spatial Analysis of Environmental Hazards

Spatial Analysis of Environmental Hazards

Determining the Flood Prone areas of Morghak river Using HEC-GeoRAS

Authors
parviz rezai
Khosrov Tajdari
Seyed Esmaeil Mirghasemi
Abstract
Flood pron areas of rivers are generally hazardous. Regionalizing these hazardous areas in terms of the degree of hazard they produce is very important for regional flood management, insurance companies and land users. Therefore, this research has tried to regionalize the potential hazard of the flood prone areas of the Morghak River using HEC-GeoRAS model as an example for all flood plains of Gillan province.

In order to develop the hydrolic model of the river, the following data were prepared.


The river profile, roughness index of the river channel and flood plain and river bank conditions were obtained from 1:2000 TIN maps.
The data were entered into the HEC-RAS model.
Then the data of the river banks and flood discharge amounts were entered and hydraulic computations were carried out.
The model results were entered into the GIS. After the requested processing in the extension of HEC-GeoRas431, the final maps of depth of river, water movement velocity, shear velocity and the flow intensity along the river channel were produced.
The maps were moved into the Google Earth and the flood area with different return periods were plotted.


The results showed the areal expansion of the 25-year return period floods of the river basin. This plain is narrow in the upper areas of the river and widens in the lower areas of the area. In the areas that there are constructions, the basin gets wider and its higher discharges causes severe hazards in the settlements around the river. The widest part of the flood plain is over the lowlands around Anzali swamp. In these lowlands the flood spreads over the vast area and making problems for the farmers and dwellers.

According to the results of this research some adaptation measures are needed in the areas where people have moved to the river channel and have built some structures. Some of these measures include vegetation planting, cement and rocky barriers and cleaning all extra wastes. The results of the study also indicate that in most of the branches the building of the channel has narrowed the channel and caused flood in the settled areas. The physiographic parameters of the river have seriously been changed and caused the severe floods in the river especially in the lower areas. The flow speed of the river changes from 4.1 m/s in the maximum discharge to .2 m/s in the very low discharge. The width of the channel has also changed from 281 meters in the maximum to 11 meters at the low discharge period. The discharge stress was between .3 to 357 newtons the overall results of the research indicate that the human interference in the river basin has caused all these hazards. And the only solution is that the humans should go out of the risky areas of the river basin. The continuation of this process in this river or in the other rivers will worsen the present hazards,
Keywords
Flood Prone
Hydrolic Model
HEC-GeoRAS Model
Arcview
Morghak Area
Carson, E. 2006. Hydrologic modeling of flood conveyance and impacts of historic overbank sedimentation on West Fork Black s Fork. Vinta mountains, northeastern Utah, USA. Geomorphology, 368-383PP.
Correia ,E.N.; Saraiva, M.G. ; Silva, F.N. and Romos, I.1999. Floodplain Management in Urdan Development Area. Part II. Gis-Based Flood Analysis and Urdan Growth Modeling.
Liang, S., and Mohanaty, C.R.C..1997. Ophimization of Gis-Bassed Flood Hazard Zoning: A case study at the Mahanady Comand Area in Catack District, Orrisa, India. Jornal of Chines Soil and Water Conservation, 28:11-20.
Mays, L.w. 1996.Reosources Handbook. Arizona State University, Megraw – Hill publication Co.
Pistocchi, A. and Mazzoli P. 2002. Use of HEC-RAS and HECHMS models with ArcView for hydrologic risk management.In Autorità dei Bacini Regionali Romagnoli by Morgagni, P. G.B. Forl, Italy.
Platte, E.J.2002. Flood Risk and Flood Manegment. Journal of Hydrology, 267:2-11.
Stephen, R. 2002. Hydrologic Investigation by the U.S. Geological Survey Following the 1996 and 1997 Flood in the upper Yellowstone River.Moutana American Water Resources Asseciattion, 19th Annual, Montana Section One, PP: 1-18.
Tate, E.C.; Olivera, F.and Maidment D. 1999. Floodplain Mapping Using HEC-RAS and ARCView GIS. Center for Research in Water Resources (CRWR).Report, NO.1-99pp.