Application of GIS, Hydraulic and Hydrologic Modelling to Investigate the Changes of Flood Inundation Characteristics due to the Construction of Dams for different scenarios, case study of Wadi Elarish

: The novelty of the research project reported in this paper is the coupling of hydrological and hydraulic modeling which are based on the first principal of fluid mechanics for the simulation of flash floods at Wadi Elarish watershed to optimize the a new location of another dam rather than Elrawfa dam which already exist. Results show that, the optimum scenario is obtained by the construction of the west dam. As a direct result of this dam, the downstream inundated area can be reduced up to 15.7 % as function of reservoir available storage behind the dam. Furthermore, calculations showed that the reduction rate of inundated area for 50-year floods is largely more than 100-year floods, implies the high ability of west dam on flood control especially for floods with shorter return period .


INTRODUCTION
The behavior of a "watershed" could be divided into two different phase. Each phase is completely different in its conditions of water flow, behaviors, parameters, and study method. The first phase, hydrological phase, within a natural unit of land which is known as watershed in which water from direct precipitation, snowmelt, and other storage collects in a (usually surface) channel and flows downward along the main stream from a point of high elevation to a point of lower elevation till it reaches the outlet station. At the second phase, hydraulic phase, the water flow is considered as channel flow from point to point, which is completely different in its characteristics, (Elhanafy, et al 2007) [1]. Some hydrological models have been applied recently to calculate the flood wave within the channel in terms of discharge verses time, hydrograph. HEC-1 as an example of these models, deals with the watershed as a lumped unit to estimate the hydrograph at the most downstream point, outlet station. It have been implement from small watersheds to a very large scale basins such as studying the effect of renaissance dam on the Egyptian water budget (Elhanafy, et al 2015) [2].
Because of the negatives of floods, the governmental agencies, communities and researchers all over the world have paid more attention to this disaster. The human capabilities can not fully control the flash floods. But, flood delineation as a result of accurate calculations of flood prediction could help in the reduction of the damage resulting from flash flood event. Many studies have used hydrological models for floods prediction (Sadrolashrafi et al. 2008 [27]), or to just estimate the flood plain (Earles et al. (2004) [28]).
Although, there are a lot of good studies in the area of flood modelling and calculation of Inundation, including those cited above, little investigations have been carried out to study the impact of a storage dam on the reduction of downstream inundated area as in the work done by Madadi et al. (2015) [25]. But none of the previous studies coupled the hydrologic simulation with the hydraulic routing as the research reported in this paper. This paper proposes utilizing of different models to investigate the effect of construction proposed dams on the reduction of flood characteristics at Elarish city and its borders. The final results are present on Google earth software to simplify the results in 3-d visualization.

Study area
Many studies consider Wadi Elarish as a real river (Hamdan 1980 [29], El Husseini 1987 [30]). Recently, a great attention from the government has been directed towards the establishment of agricultural and industrial projects in Wadi Elarish (EL-Bihery and Lachmar 1994 [31]). Unfortunately, the frequent flash floods inflicting huge economical damage and threaten any developments. Especially the main stream of Wadi Elarish divide Elarish city into two halves. To support building new communities and development in this area, Elrawfa dam was constructed in 1946 about 52 km to the south of Elarish City, to hold 3*10 6 m 3 of water (Botrous 1960 [32]). Many developments have been carried out for the dam till the storage capacity reached about 5.5 *10 6 m 3 at the end.
The destruction caused by the flash floods in January 2010 revealed the necessity to improve the system of flood protection for this area.

Location
Wadi Elarish is the largest watershed in Sinai Peninsula, Egypt, covering about 22000 km 2 that about one third of whole Sinai area and about 2% of Egypt. The main stream flows generally to the north for about 370 km from lat. 29 0 N to its outlet in the Mediterranean at lat. 31 0 09 \ N. Most of its tributaries are mainly located in Sinai and a few others comes from the neighboring Negev Desert. Drainage network is organized in a dendritic-like pattern as shown in figure 1.

Figure1.
Wadi Elarish and its location in Sinai Peninsula, Egypt.

Geology
Many studies (Moawad B.M., 2013 [26] , 2014, Elewa et al, 2013 [33], Abd-El Monsef 1991 [34]) summarize the geology of this Wadi based on topographic maps, Landsat ETM+ images and DEMs. They showed that Wadi Elarish gets most of its water from the gentle back slopes of El Tih and El Egma Plateaus in Central Sinai. El Egma Plateau is higher than El Tih Plateau since the highest point in El Egma is 1647 m a.s.l whereas the highest point in El Tih is 1400 m a.s.l. The plateaus are composed mainly of Eocene and Cretaceous. The strata go down in a northward direction at a very low slope and are locally dissected by minor faults and basaltic dykes. In the central part, the Wadi crosses over the Northern Sinai anticlines (e.g. Jabals Halal, Dalfa and Mitmitni) through some gorges of which gorge of El Daiyaga (the Narrow) is the most obvious. Elrawfa dam has been constructed on this main stream about 52 km south the outlet station. After the dam location towards the north three main streams from the east and one from the west pour their water into this main stream, El Daiyaga.

METEROLOGY
In this paper, two return periods of 50 and 100-year are taken into consideration using the available data from the Egyptian meteorological authority data for the stations that lies in the watershed. The storm of 2010 was taken into account not only because it was the worst in 100 year, but also for the calibration of the hydrological model. The analysis of the meteorological data of this storm has been studied deeply by Moawad, M.B, (2013) [26]. From the study carried out by [26], the actual rainfall of 2010 event has been taken into consideration while the rainfall is considered as 45 mm for 50 year return period, and 51 mm for 100 year return period

METHODOLGY
Providing spatial view of inundation due to flash floods is considered one of the important issues for hydrologists and watershed professionals. Therefore, the implementation of GIS in flood risk studies, flood management and floodplain mapping is becoming powerful tool for water resources applications. The research project reported in this paper starts with obtaining the DEM of the study area. Then, the hydrological simulation is carried out using HEC-WMS software to obtain the flood hydrograph at six locations.

Watershed modelling systems (WMS):
Watershed modelling systems (WMS) is implemented in this study to determine the flood water characteristics represented by the hydrographs in six locations. Two of these hydrographs are used for the calibration processes of HEC-RAS. The other four are used in the flood routing, and to analyze the effects of constructing additional dams at these locations.
The task of automatic extraction of drainage network was performed inside the WMS 9.

Geographical information system (GIS)
GIS is defined as a computer system for assembling, collecting, storing, processing, integrating and analyzing the earth related information [25,36]. Now, GIS is commonly used in different engineering disciplines especially in water quality, hydrology and hydraulics. Nowadays, advancement in the field of geographic information system has greatly facilitated the operation of flood risk and inundation mapping. Since natural hazards are spatially variables, the role of GIS is great in natural hazard management [43]. Generation a visualization of flooding and estimation probable damage due to flood are considered the most important advantages of GIS for flood studies management (Hausmann and Weber 1988 [37] ; Clark 1998[38]).
In this paper, GIS is implemented to extract the necessary information from digital elevation model for input into a HEC-RAS i.e., hydraulic model and then used to map the flood inundation or current spatial extent of floodwaters due to construction of additional dams according to specified scenarios. The main software for carrying out of the hydraulic phase of this study is ArcView GIS and its extension,

HEC-GeoRAS:
Madadi et al. (2015) [25] defined HEC-GeoRAS extension as a set of procedures, tools and utilities for the preparation of GIS data to be exported to HEC-RAS. Then, the results obtained are exported back again in a reverse direction from HEC-RAS output to be represented in GIS. It works directly with the HEC-RAS to create a geometric data file for the desired hydraulic simulation. This interface developed by the Hydrologic Engineering Center for ArcView GIS in the form of a dropdown menu in the toolbar of ArcView GIS (USACE) [39]. The computed water profiles exported from HEC-RAS are processed into HEC-GeoRAS. Indeed, the HEC-GeoRAS establishes a connection between the HEC-RAS hydraulic model and ArcView GIS, allowing for excellent visualization and analysis in a form of flood plain extent, depth, and velocity. Figure 7 shows the main stream, the bank lines, flow paths, and cross sections cut lines that describe the study area which are created in HEC-GeoRAS.

HEC-RAS:
The River Analysis System (HEC-RAS) is a one dimensional hydraulic model developed by the Hydrologic Engineering Center (HEC) of the U.S. Army Corps of Engineers (Brunner 2010 [40]).
To run HEC-RAS, all data about Cross sectional geometry, Manning's n values, hydraulic data, flow rates and boundary conditions are required as input parameters. The model equations were described by Horritt and Bates (2002) [41]. The HEC-RAS model solves the Saint-Venant equations formulated for natural channels: Where: A= cross-sectional area perpendicular to the flow; Q = discharge; ql =lateral inflow due to tributary; g = acceleration due to gravity; H = elevation of the water surface above a specified datum, also called stage; Sf = longitudinal boundary friction slope; t = temporal coordinate; and x = longitudinal coordinate. The equations are solved using the four-point implicit box finite difference scheme (Hicks and Peacock 2005 [42]).

Google earth
Many studies summarized Google Earth. But as reported by [25] Google Earth is a virtual globe, map and geographical information program that was created by Keyhole Inc.

RESULTS AND DISCUSSION
The disaster of 2010 flood event that attacked Elarish city highlighted the inefficiency of the exiting Elrafwa dam in protecting the city against violent floods. So, there is a great need to   Table 1, the most appropriate dam from four suggested location is at Ehasana. The share of the total flood water volume that attacks the city is about 15% for the three events. If this dam was constructed before 2010 flood event, it was able to reduce the max flood discharge at the most downstream location from 836 m 3 /s to 765 m 3 /s. while for a 100 year return period to should reduce it from 1403 m 3 /s to 1269 m 3 /s and for a 50 year return period to should reduce it from 886 m 3 /s to 810 m 3 /s. The total flood volume estimated using HEC-WMS that implemented in this study is in a great agreement with the measured values during the flood event of 2010. This agreement gives a high confidence level for future studies for this Wadi. More future studies should be carried out to investigate the effect of increasing Elrafwa dam on the reduction of the flood event. Also, due to the need of future development in Sinai, application of early warning system is needed. The research reported in this paper emphasis the importance of coupling the hydraulic and hydrologic coupling for the flood event simulations. Most of the hydrologic studies focus only on the flood characteristics calculation at the out let station only. The novelty of coupling both models reported in this paper is of great importance since it provides the decision maker with a clear image about the flooded area before and after any suggestion of construction additional protection structures against foods. Also, presenting the overall view in Google earth interface facilitate the imagination of the effects of both the flood event and the effect of protection structures on the inundation areas.