Fifteenth International Water Technology Conference, IWTC -15, 2011, Alexandria, Egypt

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1 IMPACT OF FLASH FLOODS ON THE HYDROGEOLOGICAL AQUIFER SYSTEM AT DELTA WADI EL-ARISH (NORTH SINAI) Abstract Shawki S Hassan Shawkiwrri@hotcom ' PhD Researcher Water Resources Research Institute (WRRI), (NWRC) Egypt Arid and semi arid areas face globally the greatest pressure to deliver and mange water recourses Water resources in Sinai Peninsula are limited to groundwater and rainfall that falls on the mountainous area which might cause flash floods In Wadi EI Arish, the quaternary aquifer is considered the main water supply that fulfills the water demands in the area However, this aquifer is bounded by the Mediterranean Sea in the North and hence it is subject to a possible sea water intrusion During the past 50 years, the aquifer exhibits a continuous decline in the water level and gradual increase in the water salinity The Quaternary aquifer is recharged mainly from the limited rainfall and the flash floods in the area Wadi EI Arish area is indentified as a flood prone area where several flash floods were recorded and resulted in significant infrastructural damages, population displacement and sometimes loss of lives The aim of this research is to Indentify the contribution of these floods to recharge the shallow aquifer In January 2010, a major flood event was occurred and caused significant changes in the hydrogeologic conditions of the shallow aquifer where Groundwater levels and water salinity are periodically measured through an extensive monitoring network The monitoring results showed that after the flood, an average increase in the water levels was occurred with a range that varies between less than 10 cm and 23 meters and also decrease in water salinity This results indicate clearly, that the recharge of the Quaternary aquifer could be enhanced through the regulation of the flood water The proper water harvesting structures are the key to maximize the benefits of flash floods to enhance the aquifer recharge rate Furthermore, this water could be used at later stage through shallow groundwater wells Key words: Flash Flood- Hydrogeology- North Sinai 1- Introduction The groundwater is the main Issue in development in the Sinai Peninsula in addition to the Seasonally flash Floods which is considered one of the most common environmental hazards The investigated area is Located along Mediterranean Sea between Lat: 31º 00' 00", 31º 11' 00" E, and Long: 33º 45' 00", 33º 56' 30" N as shown in figure (1) between Lehfen in the south, El Karrouba in the east, El- Masaeid in the west, and the Mediterranean Sea in the north The main objectives of the present work is to identify the contribution extent of flash flood to recharge the shallow groundwater aquifer at Delta El Arish The water levels are now below sea level over a large area which indicates that the abstraction exceeding natural recharge and is

2 being supported by lateral inflow from adjacent area, from depleting storage and from the return flow of domestic waste water From the results of chemical analyses,well monitoring network and runoff measurements before and after flood we estimate the water quantity feeding the groundwater aquifer at outlet of the Delta 2- Topography and Geomorphology The area is flat in general with a little slope from south to north Delta Wadi El-Arish is Considered the main geomorphologic features where the wadi width attains one kilometer in the outlet to more than 3 kilometers in the middle part the presence of sand dunes accumulations from east and west directions with elevation ranges from 40-50m and it increases gradually toward the west till El-Arish city The main stream of the wadi is covered by vegetation 3- Geological Setting Fig (1) Location map of the study area The geology of the area can be classified into the following lithostratigraphic units from younger to older as follows figures (2) 3-1 Holocene deposits These deposits include: Sand dunes accumulations: which cover the most area of study in the form of beach sand dunes with ripple marks shape, sand sheets and scattered lenses intercalated within the wadi deposits

3 Beach deposits: it extend along the coastal shore line from El-Arish to Rafah beyond Gaza in the form of friable sands to consolidated sandstone as a result of calcareous material as calcium carbonate Recent wadi deposits: which known as wadi fill that cover the main stream of wadi El-Arish and its tributaries, and composed of sand, clay and silt with thickness varying from 4 to 28 m 3-2 Pleistocene deposits Fig (2) Simplified Geological map of the study area These deposits cover the most area of eastern coast of Sinai Peninsula and it can be classified as follows: Wadi deposits of delta wadi El-Arish which cover the most area of the main stream of wadi El-Arish with thickness ranging from 47 to 144 m and composed mainly of sand, silt, clay and gravel Calcareous sandstone unit (Kurkar) This unit forms the lower part of the quaternary successions along the EL-Arish Rafaa coastal zone, and extends for km from the coast It is bottomed by the Miocene to the north of the airport and by the Cretaceous carbonates/shale complex in the faulted block at Lahfan 3-3 Miocene deposits These deposits are not outcropping on the surface of the area but it occurs underneath the Quaternary sediments in the form of clay to the south of El-Arish airport

4 3-4 Eocene deposits These deposits were found in the form of sandy clay, marl and marly limestone to the north of Lehfen, and in the form of clay and gypsum near the coastal belt of El-Arish 4- Hydrogeology of the Study area 4-1 Aquifer system This aquifer occurs along the coastal belt and composed of continuous layers from sand dunes in the upper part, wadi deposits or beach deposits in the middle part while the lower one is composed of calcareous sandstone (fossiliferous) called locally kurkar, these aquifer can be described as follows: sand dunes (Holocene) These dunes occur along the coastal belt and extend in land toward the delta of wadi El-Arish and it form in the direction of wind and composed mainly of fine grained sand From the tested wells in the south western part of El-Arish city it appears that these sand dunes have no groundwater but it assess in the groundwater recharge of the lower layer Quaternary deposits (Pleistocene) These deposits are considered the main aquifereous zone for water supply in El-Arish area and composed mainly of sand gravel intercalated with clay or silt in part with thickness ranging from 40 to 60 m, while the saturated zone varies from 10 to 30 m thick These layer represented the upper Pleistocene and it extends some 25 km to the south of El-Arish The main source of recharge is the rain or from deep seated layers through south Lehfen fault and buried wadis The presence of clay layers in parts make the aquifereous zone semi-confined in the northern part and unconfined to the south of El-Arish airport Calcareous sandstone (Kurkar) This auriferous zone refers to the lower Pleistocene and composed of fossiliferous calcareous sandstone this zone covers the coastal belt of the Mediterranean sea and extends to a distance varying from 10 to 25 km southward it occurs underneath the wadi deposits and overland the Miocene deposits to the south of El-Arish airport, underneath the carbonate rocks and overlain the Pliocene deposits near the beach 4-2 Aquifer geometry The Quaternary deposits extend from the Mediterranean coast in the north to about km in the south, from the data collected from tested wells in El-Arish area it

5 appears that the Lower boundary of the aquifer tilted from south at Lehfen to north at the coast with thickness ranging from few meters at Lehfen to more than 120 m in the middle of delta wadi El-Arish Based on the data collected a number of hydrogeological cross-sections were constructed which illustrate the extension and thicknesses of the water bearing formations figures (3-a) and (3-b) fig (3-a) Hydrogeological cross-section at Delta of wadi El-Arish Fig (3-b) Hydrogeological cross-section at Delta of wadi El-Arish

6 4-3 Aquifer potentiometry From the periodical inventory carried out by WRRI staff and according to the potentiometric surface map figure (4) which shows that: 1 The zero potentiometric contour line is expanded to enclose most El-Arish area between the airport in the south to El-Arish in the north and El-Massaid in the west to El-Arish / Lehfen road in the east 2 The biggest depletion in the water level was recorded during the period due to the number of wells in that period and randoum increasing of drilling water wells in addition to the high pumping rates that more than recharge volume Generally, the depletion of static water level was noticed clearly at piezometer no 13 (-531 m) bsl due to the high abstraction and increasing of cone of depression, also at test well no 14 to the south east of El- Arish city accordingly, the delta wadi El-Arish area can be classified into four parts: Part-1: The static water level varies from 1 to 15 m amsl (in the south) Part-2: The static water level varies from -05 to -25 m bmsl (North and around El-Arish city) Part-3: The static water level varies from -05 to -5 m bmsl (East and middle of El-Arish) Part-4: The static water level varies from -05 to 10 m bmsl (in the north) Fig (4) Potentiometric Surface map at Delta of Wadi El-Arish

7 4-4 Aquifer hydraulic parameters Based on the pumping tests that carried out on the test wells in delta wadi El-Arish to estimate the hydraulic parameters and their Interpretation carried out by WRRI staff and JICA (1992) which shows that the hydraulic conductivity values of Kurkar aquifer varies from 20 and 260 m/d and the transmissivity ranges between 3x10-3 to 9x10-3 /d and storativity 2х10-2 to 5x Groundwater Salinity The groundwater salinity map of the Quaternary in EL-Arish area at August 2010 is shown Fig (6) indicates several salinity zones which are: i- Low Salinity zone: Occupied the area to the south of the airport and the area to the west and southwest of EL-Arish town in this zone the groundwater salinity ranges between ppm ii- Medium Salinity zone: Occurred in the area between EL-Arish town in the west, EL-Arish Lahfan road in the East, the airport in the south Within this zone, the water supply and irrigator well fields are located The groundwater salinity in this zone ranges between pm iii- High Salinity zone: which extended along the eastern side of the EL-Arish- Lahfan road In general, the groundwater Salinity ranges between 3500 and 6500 ppm This highly salinity zones can be reasoned to the fact that most of the wells in this area tap both the alluvial gravels and the marine kurkar unit which is brackish water bearing and/or to the possibility of being contaminated by saline water from the adjacent pre- Quaternary aquifers which have been brought in contact with the Quaternary aquifer by the NE-SW fault systems Its obvious from periodical monitoring to the groundwater aquifers (Cairo university report1989) and (GWS) sector project (2005) deterioration groundwater levels and gradation of salinity as shown fig (5) due to random drilling Wells and over pumped to cover water demands TDS PPM Swl Water level decline TDS PPM Swl Fig (5) the relation between salinity and water level along time for groundwater well at delta wadi EL-Arish

8 Fig (6) ISO salinity map at Delta Wadi El-Arish 5- Water balance and aquifer Recharge The water Resources Research Institute (WRRI) staff estimated the abstracted water from the wells which was found to be about /day (2525 m//year) also estimated the volume of precipitation which was found to be about 57 m//year, which indicates that abstraction exceeding natural recharge, and is being supported by lateral inflow from ad-jacent area, from depleting storage and from the return flow of the domestic waste water the Quaternary aquifer is recharged by only 50% of these volume so, the water position is critical and must be managed well to avoid the deterioration of groundwater in both space and time and also quantity and quality The following table and fig (7) shows the abstracted water from wells through the years 1956 till now

9 Table (1) Historical Groundwater Extraction and Population of El Arish Area Years No of Wells > 600 Domestic /day Irrigation /day Total /day * > Population > > > > Fig (7) Abstraction rates with Time 6- Hydrological Setting of wadi El-Arish The drainage basin area of the Wadi is about km2 (about one-third of the Sinai Peninsula area) The wadi morphology is characterized by steep slopes in the upper part of the basin, decreasing while approaching the sea as shown in the digital elevation model (DEM) figure (8)

10 Fifteenth International Water Technology Conference, IWTC -15, 2011, Alexandria, Egypt Figure (8) Digital elevation model El-Arish drainage basin consists of a number of main streams and by Using the Watershed Modeling System (WMS) software, the drainage basin is divided into 39 sub-drainage basins with areas ranging between 51 and 1353 km2 Water Resources Research Institute (WRRI) has a rainfall measurement stations covered the entire area of Sinai Peninsula where Wadi El Arish is affected by Some of measured stations as Shown Figure (9) Figure (9) Location of rainfall measurement stations

11 In January 17th 2010, a heavy rainfall covered most of Sinai area and caused huge flash floods at wadi Al Arish outlet TheWRRI rainfall stations measured this event, where the data are analyzed as shown in figure (10) Storm 17 & 18 January 2010 Rainfall (mm) El Gudirate Al Rawafaa Nukhl El Themid El Hasana 0 1/17/10 18:00 1/17/10 19:00 1/17/10 20:00 1/17/10 21:00 1/17/10 22:00 1/17/10 23:00 1/18/10 0:00 1/18/10 1:00 1/18/10 2:00 1/18/10 3:00 1/18/10 4:00 1/18/10 5:00 1/18/10 6:00 1/18/10 7:00 1/18/10 8:00 1/18/10 9:00 1/18/10 10:00 1/18/10 11:00 1/18/10 12:00 1/18/10 13:00 1/18/10 14:00 1/18/10 15:00 1/18/10 16:00 1/18/10 17:00 Time (hr) Figure (10) Al Arish rainfall measurement data 7- Estimation of Flash Flood Cotribution to recharge groundwater aquifer 7-1 from rainfall Data Rainfall data of all effective rainfall stations for the storm is input to the Hec-1 hydrologic module of the WMS software Also, the land use and soil type map is used to estimate the water losses of each sub-basin and accordingly the excess rainfall which causes runoff as shown fig (11) Figure (11) Runoff volume for 17 January 2010 storm

12 PReR IRaR FRaR IRaR = + ar + (1) Fifteenth International Water Technology Conference, IWTC -15, 2011, Alexandria, Egypt Losses Estimation using SCS Loss Method The rainfall-runoff relationship in this method is derived from the water balance equation and a proportionality relationship between retention and runoff The SCS rainfall-runoff relationship (shown in the Figure 12) is given by: Rainfall = PReR IR FRaR P e ( P I = ( P I a a ) 2 ) + S (2) where: P S = the rainfall depth (mm) = the depth of excess rainfall (mm) = the initial abstractions (mm) = the volume of total storage (mm) = Continuing abstraction S( P I a ) Fa = p Ia P I a + S (3) Storage includes both the initial abstractions and total infiltration The initial abstraction is a function of land use, infiltration, detention storage, and antecedent soil moisture The initial abstraction and the total storage are related in an empirical statistical equation which is given as: 02S (4) Substituting equation (4) into equation (2) yields: 2 ( P 02S) P e = (5) ( P + 08S) The storage S (in millimeters) is obtained using the formula: Precipitation rate I a P e Losses estimation using SCS method Time Fig (12) The SCS rainfall-runoff relationship S = 254 (6) CN where: CN is the curve number that can be obtained from standard tables for different combinations of land use and land cover, hydrologic soil groups, and

13 hydrologiccondition The hydrologic soil group reflects a soil s permeability and surface runoff potential The SCS-CN is used to estimate the water losses of each sub-basin and accordingly the excess rainfall which causes runoff The land use and soil type map is used to estimate the water losses of each sub-basin and accordingly the amount of infiltration The estimated curve number for the sub-basin at the outlet is about 71 and the rainfall at 17 January 2010 is about 223 mm By substituting with these data in the previous equations, the continuing abstraction is about 5 mm and accordingly the infiltration amount is about cubic meters 7-2 From Water Level Measurments The monitoring of Groundwater level After the flood evant in 17/1/2010 represnts an Increase of water level than that measured before By (10cm to 2,03m) as shown at table (2) and figs (13,14) due to the nature of the aquifer constituents in Delta wadi EL-Arish which contains sand, gravel and silt that increase the Infiltration rates which Improve the aquifer recharge and Groundwater quality The main focol point is the central flood region along the main stream which Located South of EL-Arish Twon From hydrogeological point of view we try to estimate the water volum by using the GiS technique (vertical mapper) to calulate the total area covered by countor lines 119 as shown fig (15) and we assuming the saturated thickness of the aquifer (40m), total porosity is ( ) from these parameter we calculate the water volum feeding the aquifer by about 900 x meters Table (2) water levels and EC measurments before and After flood Well no Long Lat Water level Before Flood (m) Water level After Flood (m) Difference (m) EC Ms/cM3 before Flood EC Ms/cM3 After Flood N N N N N N N ? N ? N N tw N N pz pz

14 Fig (13) Water level map before flood Fig (14) Water level map After flood

15 Conclusions Fig (15) different areas covered by contour lines From the Resherce its clear that there is a deterioration in the groundwater levels decline and increasing of water salinity in EL-Arish area, which indicates that the abstraction amounts are exceeding the natural recharge which depending mainly on the annual amount of rainfall Therefor, the water balance is in critical situation which lead to good management to exploit the water resources The monitoring results showed that after the flood, an average increase in the water levels was occurred with a range that varies between less than 10 cm and 23 meters and also decrease in water salinity, the amount of water calculated from water level is about cubicmeter, and from the rainfall data is about cubicmetr This results indicate clearly, that the recharge of the Quaternary aquifer could be enhanced through the regulation of the flood water

16 Recommendations 1- The abstraction rate exceeding the recharge rates which causes increasing in water salinity and to keep the aquifer from deterioration it is necessary to exploit the rainfall water that collected in front of EI-Rawafaa dam to recharge the aquifer in Delta of wadi El-Arish 2- It is prefer to use artificial Recharge through pipe lines from rawafaa dam to Injected water directly to agella wells to Improve the quality of limestone aquifer 3- Under no circumstances drilling new water wells except the drilling of the abundant wells, and water counters should be installed 4- A network should be constructed to connect all the water wells working by electricity to work automatically 5- The transported Nile water should be increased to cover the water demands of population growth 6- Increasing of environmental awareness of people to keep the water clean and avoid pollution of groundwater aquifer REFERENCE 1- Water Resources Research Institute (WRRI), Groundwater Sector (GWS), (2006); Water Supply for Bedouin Settlement from Rabaa village to EL-Arish (North Sinai) submitted to Islamic Bank for Development, Jeddah 2- Cairo University Faculty of Engineering, (1989a) Groundwater management study in / EI Arish Rafaa plain area Phasel, main report, vol 1,Water Resources Research Institute, Ministry of Public Works and Water Resources 3- Water Resources Research Institute (WRRI) and JICA, (1992); North Sinai Water Resources Study in the Arab Republic of Egypt, Final Report