Civil and Environmental Research www.iiste.org ISSN 2224-5790 (Paper) ISSN 2225-0514 (Online) Vol.9, No.2, 2017 65 Rainfall Floods as a Result of Land Use Alteration in a Syrian Refugee Camp in Jordan Saad M. AlAyyash Civil Engineering Department, Al al-Bayt University, PO box 130040, Mafraq, Jordan Abstract The Zaatri Refugee Camp (ZRC) established summer 2012 shortly after the Syrian conflict started. Due to high flux of refugee fled the conflect south of Syria to Jordan and in a short notice, the international organizations with the Government of Jordan started to establish the camp with limited data on socio-economic and environmental impacts of the selected site. The camp is located in a nearly flat area which forms natural soil pan that used for cultivation. One of the environmental impacts for the selected site is the flooding in parts of the camp due to altering the hydrologic response of the area. This alteration is resulted in two ways: the first on is the building of earth wall around the camp which stops the runoff floods from getting into the natural water courses, the second alteration is the building of dense metal houses with compacted pathways in between. After establishing the camp, the land use changed completely, dense metal housings are built covering around 50% of the area. Networks of compacted roads between the housing blocks are built using imported crushed limestone aggregates. The change in land cover increased the Curve Number (CN) from 84 for the natural agricultural land to 92.5 for the built up area. The increase in CN due to altering the hydrologic parameters within the camp area increased the runoff depth by 82% to 614%, this resulting in more flood water trapped inside the boundaries of the camp. The flood volumes that accumulated can cover more than 10% of the camp area with average water depth 25 centimeters (cm) for 25-years return period storms. In other hand, the storms event that most probably occurs every other year (2-years return period) could result in flood that covers about 1.5% of the camp area with water depth that reaches 25 cm. Keywords: Rainfall floods, Land use alteration, Zaatari Refugee Camp, Jordan 1. Introduction Flood risk analysis for an area requires modeling the runoff resulting from up normal rainfall storm (Apel et al. 2006). In order to model the flood risk, the rainfall-runoff modeling requires good delineation of watersheds and estimation of physical and hydrological parameters of these watersheds as well as metrological data (Monte et al. 2016). The flood risk could be in a regional scale where large areas are at risk of flooding or it could be in local scale where small lower areas can be flooded due to limited amounts of rainfall. The flood modeling at a regional scale has limited accuracy due to variation of modeling input such as rainfall depth at a regional scale (Knebl et al. 2005). The backbone of flood risk analysis is the rainfall-runoff hydrological modeling, there are several techniques for runoff modeling. The useful technique for flood analysis is the use of distributed modeling in a raster based modeling environment (Khan et al. 2011, Gharagozlou et al. 2011, Horritt & Bates 2001). The SCS-CN method is widely used to model runoff using rainfall events (Zaharia et al. 2015). In ungagged watersheds, there are limited data to use complex models, the SCS-CN method needs simple input data that can be derived from physio-geographic data such as Digital Elevation Model (DEM), soil type and land use/cover for the targeted area. (Miller & Clancy 2017, Cronshey 1986). In the SCS-CN method the runoff depth (R) is calculated for a given storm that has a rainfall depth (P) using one parameters, the potential storage (S) which is calculated using the Curve Number (CN). The CN for a given watershed is derived using the characteristics of the watershed such as soil type, land use and man-made practices if any (Cronshey. 1986). The S value (in millimeters) is calculated as: 254 25400 - = CN S (1) The SCS-CN method suggests that the runoff occurs when the rainfall depth exceeded the initial abstraction (Ia) which is in average equal 0.2 the potential storage (S) (Cronshey. 1986). The runoff for storms more than 0.2S is calculated as: