groundwater relationship using automated base-flow separation ...

Investigation of the potential surface– groundwater relationship using automated base-flow separation techniques and recession curve analysis in Al Zerba region of Aleppo, Syria Rudy K. Abo & Broder J. Merkel

Arabian Journal of Geosciences ISSN 1866-7511 Arab J Geosci DOI 10.1007/s12517-015-1965-6

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Author's personal copy Arab J Geosci DOI 10.1007/s12517-015-1965-6

ORIGINAL PAPER

Investigation of the potential surface–groundwater relationship using automated base-flow separation techniques and recession curve analysis in Al Zerba region of Aleppo, Syria Rudy K. Abo 1 & Broder J. Merkel 1

Received: 28 September 2014 / Accepted: 21 May 2015 # Saudi Society for Geosciences 2015

Abstract The management of water resources requires an adequate understanding of the relationship between the various components of the hydrological cycle. The accelerated urbanization and agricultural development impose the concern about the sustainability of water resources, particularly in arid and semi-arid regions. In such environments, water scarcity and drought often lead to intensive groundwater abstraction which can adversely affect the hydrological system. Severe over-exploitation of groundwater has been observed on the Aleppo basin of the Al Qweek River. The Al Qweek valley constitutes the central part of the study area (southwestern parts of the Aleppo basin). The region is characterized by a semi-arid climate with an average annual precipitation of 325 mm. The intensive exploitation of the upper aquifer in the catchment is responsible for a continuous decline of the piezometric levels with an average of 1.8 m/year. The objective of this study was to investigate the relationship between the upper aquifer and the Al Qweek River within the catchment boundary using streamflow and hydrograph separation techniques by means of daily discharge data for both the Al Qweek and Al Qwaak rivers. HydroOffice was used for the base-flow separation, flow duration curves (FDC), and recession curve displacement analysis. Furthermore, groundwater recharge was estimated by means of RECESS and RORA. This is the first study using the hydrograph separation method in this region to our knowledge. The results indicate a proportional relationship between the surface and groundwater with an average discharge fluctuation that ranged from 0.30 to

* Rudy K. Abo [email protected] 1

Department of Hydrogeology, TU Bergakademie Freiberg, Freiberg, Germany

0.20 m for the Al Qweek and Al Qwaak rivers, respectively. The results also revealed a dominant base flow in the catchment that ranged from 86.3 to 88.2 % of the total flow with a computed base-flow index that varied from 0.85 to 0.90 in all gauge stations, indicating a stable flow regime in the region. Furthermore, the high base flow is resulting in high permeability conditions of the upper aquifer and low direct surface runoff. The visual interpretation of the FDC suggests sustained base flow from groundwater storage. The low-flow index indicates an average contribution of groundwater storage of 45 to 58 %. The result of recession curve analysis shows a recession constant from 0.8 to 0.9 indicating a dominant interflow and low overland runoff. Furthermore, the results also show that estimation of groundwater recharge using RORA is inappropriate for the region of interest. Keywords Surface–groundwater Interaction . Base-flow separation . Recession curve analysis . Net groundwater recharge

Introduction Surface and groundwater interaction is an important factor for efficient management of water resources and the development of policies for soil water environmental protection, particularly in regions with a shallow distributed groundwater table. Surface water can interact with groundwater in two basic ways in nearly all watersheds controlled by the difference between the water table and river stage: river discharge into the groundwater table through the streambed, when the river stage is higher than the groundwater table (losing stream), or groundwater flow to surface water as a base flow if the groundwater table is higher than the river level (gaining stream) (Winter 1999; Healy and Scanlon 2010). That can be distinctly

Author's personal copy Arab J Geosci

observed when surface and groundwater systems are connected together (humid and sub-humid regions), but in some regions, losing steams can be disconnected from the groundwater system by an unsaturated zone, as in most arid and semiarid regions with high depth to groundwater table. Surface water in such environments forms an important source of localized groundwater recharge (Scanlon et al. 2002). This relationship between surface and sub-surface water is associated with the concept of recharge as an essential component in the water balance of any watershed (Freeze and Cherry 1979). A water-losing stream is usually associated with focused recharge and occurs in karst environments as well as arid and semi-arid environments. It occurs in areas of valleys, steep slopes, and unlined canals and from artificial water bodies (Seiler and Gat 2007). In contrast, groundwater discharge (base flow) into a gaining stream is typical for humid climate. Seepage flux in both cases of losing and gaining streams is controlled by the hydraulic gradient between the surface water level and groundwater table. If groundwater is connected to the stream, then the discharge from the losing stream into the groundwater represents the actual recharge, while the existence of an unsaturated zone makes any estimation of groundwater recharge more complex since not all infiltrated water may reach the water table, and therefore, the stream loss represents the potential recharge. However, the focused recharge from ephemeral streams is the dominant infiltration type in the arid and semi-arid regions while streams in humid areas are generally affected by diffuse recharge from sub-surface sources (Healy and Scanlon 2010). Natural groundwater recharge and seepage direction under prevailing arid conditions are more frequent compared to humid areas and highly influenced by precipitation duration and intensity, surface topography, changes in the slope of the streambed, and the meandering in the stream channel (Simmers 1988; Winter 1999; Gee and Hillel 1988; Arnold and Allen 1999). Furthermore, recharge from the losing stream downward through the unsaturated zone to the water table depends on the infiltration capacities of the riverbed. This can be negatively affected by chemical and biological processes and external/internal sediment clogging that can significantly reduce the permeability of the streambed and hence the groundwater recharge (Schälchli 1992; Calver 2001). Therefore, the study of river infiltration into an aquifer requires consideration of the various hydraulic properties, as well as the physical and chemical soil composition of the streambed. The estimation of the exchange rate between surface and groundwater from streamflow data is commonly used in humid and sub-humid regions and can be used carefully in arid and semi-arid regions as well (Xu and Beekman 2003). Various techniques have been developed to estimate groundwater recharge and in the study of surface and groundwater interaction using streamflow data, including physical approaches such as

stream water budget, seepage meter, Darcy’s methods, streamflow duration curve, and streamflow hydrograph separation (e.g., hydrograph separation and rescission curve displacement). The chemical method is one of the most important methods to estimate groundwater recharge by integrating isotopic composition into the hydrograph separation and using tracer techniques (Scanlon et al. 2002; Healy and Scanlon 2010). Hydrograph separation methods of gaining or losing stream are usually used by hydro-geologists to estimate groundwater contribution or surface water infiltration from streamflow data including the base-flow separation, streamflow duration curves (frequency analysis), and recession analysis (Brodie and Hostetler 2005). A base flow is defined as groundwater discharge to a stream or other surface water bodies contributing to the surface runoff and interflow. However, using base flow to estimate groundwater recharge is based on the water budget equation, which considers the change in groundwater storage, pumping of groundwater, and evapotranspiration from shallow groundwater. Base-flow analysis for stream hydrography has been a well-known technique since the beginning of the last century, and started with theoretical and empirical work by Boussinesq (1904). Many valuable reviews of base-flow separation methods have been written by Hall (1968), Appleby (1970), Nathan and McMahon (1990), Tallaksen (1995), and Smakhtin (2001). In addition to the stream base-flow analysis techniques, stream water budget methods are often used to understand the interaction between a river and groundwater, and usually applied in arid and semi-arid regions (Healy and Scanlon 2010). These methods use the difference in river discharge at the upstream of the reaches and the downstream, which can be a positive value, indicating groundwater discharge (base flow), or negative in the case of a losing stream (focused groundwater recharge). Stream water budget may include high uncertainties due to error in discharge measurement, precipitation, and measured evaporation from surface water (Rantz 1982). However, stream water budget requires careful planning of the seepage to cater for the various terms in the budget equation (Eq. 1): Qout ¼ Qin þ P−Esw −ΔS sw þ Roff þ Qtrip þ Qinter þ Qseep

ð1Þ

where Qout and Qin are the stream discharge at the downstream and upstream, respectively; ΔSsw is the change in stream storage over time; and Roff is the overland runoff. P is precipitation and Esw the evaporation from surface water; Qtrib is flow from tributaries, Qinter is the interflow through the unsaturated zone, and Qseep can be base flow or groundwater recharge. Software development in the last two decades offers nowadays computerized solutions for hydrograph separation using various types of algorithms and filtering options promoting the possibility of analyzing complex hydrographs and reducing the time of analysis (Rutledge 1998; Arnold and Allen


1999). An example of an automatic separation program is HYSEP (Sloto and Crouse 1996) which offers three types of filtering options: local minimum, fixed, and sliding interval. Syria belongs to the arid and semi-arid countries with limited water resources and a growing population. As is the case of many developing countries in the region, the increasing demand for food and water and accelerated urbanization have exhausted an important part of the water resource and this makes water sustainability the top management priority of the country. The incomplete framework for analysis and inadequate knowledge have led to high uncertainty in the estimation of groundwater recharge and other components of the hydrological cycle (Hamdy et al. 1995). However, proper management of the water resource and projects carried out between 2004 and 2010 in Syria as a cooperative effort between the Syrian Ministry of Irrigation (MOI), the German Federal Institute for Geosciences and Natural Resources (BGR), and the Arab Center for the Studies of Arid Zones and Dry Lands (ACSAD) improved the water situation in the Aleppo basin significantly. Base-flow separation and recession curves analysis have been widely used in arid and semiarid environments. Welderufael and Woyessa (2010) used baseflow separation and frequency duration methods to analyze the flow regime of the Modder River in Central South Africa. The base-flow separation technique was also used in north central Iran to study the magnitude and dynamics of groundwater discharge of the Hableh Roud River (Rouhani and Malekian 2013). Base-flow fluctuations of the Yangtze River in the central part of Qinghai–Tibet and its relationship to the precipitation and air temperature were used to investigate the interaction between groundwater and the climatic system (Qian et al. 2012). Close to the Middle East, the nonlinear base-flow recession analysis was implemented to investigate the nonlinear storage–outflow relationship of the Culap intermittent river in the southeastern parts of Turkey (Aksoy and Wittenberg 2011). The objective of this study was to assess the potential net groundwater recharge in Al Qweek valley resulting from the seepage into the Upper Quaternary and Helvetian aquifer in the region. Moreover, the variability in the flow, low-flow frequency as well as the relationship between Al Qweek River and the tributary of Al Qwaak River and groundwater over the modeled years were investigated. Hydrograph separation and recession curve displacement analysis are therefore the main tasks of this paper, considering the fluctuation in the water table and precipitation.

Study area Location and climate Al Zerba catchment constitutes the central and southwestern parts of the Aleppo basin, north of Syria (Fig. 1). The catchment

covers a total area of 573.58 km2 and has a relatively flat topography with gentle slopes (7 to 8 %). Average local relief varies between 260 and 400 m, with an average elevation of 300 m a.s.l. The area is surrounded by three main hills: Jebel Simon in the north, Jebel Al Hass in the east, and Tel Hadya in the southwest. The study area is characterized by Mediterranean climate with rainy cold winters and dry hot summers. The long-term average annual precipitation ranges from 300 to 350 mm/year in Aleppo and Tel Hadya, respectively (period 1964–2005). The air temperature fluctuates sharply during the year. The average mean annual air temperature is 18 °C, and ranges from an average of 7 °C in winter to 27 °C in summer (Fig. 2). The long-term annual potential evapotranspiration reaches up to 1800 mm/year (period 1957–1990). According to UNEP (1997), the region is classified as a semi-arid climate with an average aridity index of 0.25. Geology Ponikarov (1964) described the geology and stratigraphic succession of Syria; the Helvetian deposits (N1h) are the main outcropping formation in the region and cover considerable areas of the Aleppo basin. They are mainly determined by organogenous limestone with an average thickness of 200 m. The Upper Miocene basalt occupies the eastern part of the catchment (Jebel Al Hass and Kanaser Valley). The reported thickness of basalt flow ranges from 10 to 50 m (Selkhozpromexport 1979). The deposits of the Middle and Upper Eocene (P22+3) spread over large areas of the Aleppo basin. They consist of clayey and nummulitic limestone with an average thickness that ranges from 100 to 200 m. The deposits of this stage outcrop on the hilly lands in the northern and northeastern parts of the study area (Aleppo uplift, Kanaser Valley) (Asfahani and Radwan 2007). The Quaternary deposits of the Upper Pleistocene (Q3+4) fill the interior parts of the Al Qweek Valley and Al Matah depression to the south of the study area. The average thickness of the Quaternary deposits varies from 5 to 10 m. The Aleppo basin is located within the mobile part of the Arabian platform. The Al Bredeh fault represents the main tectonic structure in the study area. It has a SE–NW striking direction. Unfortunately, no detailed information is available about this fault. A simplified geological map is shown in Fig. 3. Hydrogeological setting The hydrogeological system of the Aleppo basin is generally characterized by three main aquifers. The upper aquifer is determined by clastic limestone of the Helvetian with an average thickness of 120 m. The average groundwater depth ranges from 70 to 90 m. The aquifer has a good productivity and fresh groundwater. Due to the over-exploitation during the last three decades, the groundwater levels significantly declined up to 20 m in some areas (Luijendijk 2003). According


Fig. 1 Location of catchment area

to the report of the Syrian General Company of Hydraulic Studies (GCHS 1999), about 3 to 31 million m3/year of water is being extracted from the Neogene aquifer for drinking and industrial purposes, while more than 153 million m3/year is used in irrigation. Unfortunately, there is no authoritative information about groundwater pumping rates in the study area. The second aquifer is identified by the alternation of fractured marly and clayey limestone of the Middle Eocene with an average thickness of 200 m (Al-Charideh 2012; Stadler et al. 2012). The third deep aquifer system consists of dolomitized fractured limestone and belongs to the Upper Cretaceous stage (Cenomanian/Turonian) (Selkhozpromexport 1979; Brew et al. 2001). The average aquifer thickness varies from 250 to 350 m. The aquifer system and water quality of Aleppo basin have been described in detail by Gruzgiprovodkhoz (1982), Wagner (1997), and BGR and MOI (2004). According to the hydrogeological investigation in the Aleppo basin conducted by Selkhozpromexport (1979), the Helvetian aquifer is mainly recharged by infiltration of precipitation and lateral

inflow of groundwater from adjacent horizons and complexes in the eastern and southern parts of the basin. The water abundance in this aquifer is extremely variable, and the yield from pumping wells ranges from 1.3 to 5 l/s with an average specific yield of 0.05 and hydraulic conductance ranges from 0.18 to 1.19 m/day. In the past decade, several techniques have been implemented to estimate the groundwater recharge within the Aleppo basin. The average groundwater recharge of the region is determined to be 12 mm/year using a chloride mass balance (Luijendijk and Bruggeman 2008) and 30–60 mm/ year as estimated by Wolfart (1966), Selkhozpromexport (1979), Gruzgiprovodkhoz (1982), JICA (1997), Martin (1999), and Abo and Merkel (2015), applying water balance methods and infiltration from the unsaturated zone. Hydrology The surface drainage system is defined by a dendritic pattern where water channels are formed irregularly in the alluvium


Fig. 2 Long-term average monthly precipitation P; potential evaporation PE; and the temperature variation for both meteorological stations of Aleppo (1946–2005) and Tel Hadya (1995–2008)

sediments (alluvial substrate) of the Al Matah depression. Two main meandering streams are located in the region: Al Qweek River, which is considered a perennial stream, and Al Qwaak as ephemeral channel. Generally, the development of the river is interrupted by changes in valley width and gradient, and the convergence of tributaries with different discharge, water quality, and sediment regimes draining catchments of different geological, climatic, and biogeographical characters (Starkel 1995; Charlton 2007). Therefore, a fluvial river can be divided into different functional sectors (Petts and Amoros 1996).

Al Qweek River is characterized by relatively straight channels in the north (upstream/production zone) with high discharge value carrying the fine suspended materials of clay particles, silts, and sands through the interior parts of the Aleppo basin/Al Zerba catchment (transfer zone) into the Al Matah depression. In the south, the river forms highly convoluted meander bends and flat drainage. Despite the Al Qweek River being the main surface water resource of the Aleppo basin, only a few studies are available on the river, particularly those dealing with the environment. However,


Fig. 3 Aquifers and geological map of the catchment according to Ponikarov (1964) and JICA (1997), modified after Abo and Merkel (2015)

Al Qweek River originates from the Turkish territory with high slops towards the south and ends in the depression of Al Matah (Al Seha marsh). The area of Al Qweek catchment is 4698 km2; about 3344 km2 of the total area is located in Syria with a length of 108 km (BGR and MOI 2004). The average daily river discharge of Al Qweek River within the catchment area ranges from 0.2 to 0.5 m 3/s in dry season and up to 3.5 m3/s in winter (2002 to 2006), while 0.47 m3/s discharges from Al Qwaak stream in the wet season. According to the final report of Gruzgiprovodkhoz (1982), Al Qweek River is perched relative to the water table in the Helvetian aquifer. The latent discharge from the Helvetian limestone into the river seems to occur because of the fact that in the extremely inhomogeneous fissured stratum of limestone, the direct vertical infiltration is hindered and the bulk of water seeped from the surface in the basin has time to drain to the river. Figure 4 is a schematic model of the hydrogeological system and the main components of the hydrological cycle of the region.

Agriculture and soil types In 2007, agriculture contributed about 20 % to the gross domestic product (GDP) in Syria (FAO 2008). The accelerated socio-economic development in the country increased the total irrigated areas of the Aleppo governorate from 123,300 ha in 1994 to 218.3000 ha in 2010 (CBS 2011). The study area is intensively cultivated, with a total irrigated area of 11,000 ha (Abo and Merkel 2015). Wheat, barley, and legumes are considered as the main planted crops in the region. The study area is covered by fine clay, thermic soils which are predominantly in the central and southern parts of the region (Tel Hadya and Al Zerba), changing into fine loamy in some areas (Ryan and Masri 1997). The average soil thickness ranges from 1 to 1.5 m. According to the Syrian soil map provided by ACSAD (1985) and the Harmonized World Soil Database (Nachtergaele and Batjes 2012), the Chromic Luvisol soil is the dominant soil type in the northern parts of the catchment with an average thickness of 1 m. Detailed information about soil texture composition is given in Table 1.


Fig. 4 Schematic model of aquifer system, hydrological components, and the location of gauge stations within the catchment area. Modified after Charlton (2007)

Materials and methods Table 1 Major soil properties in the northern (Aleppo) and southern (Tel Hadya) parts of the Al Zerba catchment Depth (cm)

Properties

0–30

Texture (%)

30–150

Texture class

Sand Silt Clay

Bulk density (g/cm3) Field capacity (m3/m3) Welting point (m3/m3) Organic matter (%) Texture (%) Sand Silt Clay Bulk density (g/cm3) Field capacity (m3/m3) Welting point (m3/m3) Organic matter (%)

Aleppoa

Tel Hadyab

26 27 47

10.15 29.95 59.9

1.35 0.41 0.27 0.20 21 25 54 1.40 0.43 0.31 0.8 Clay

1.30 0.30 0.18 0.86 6.85 27.05 66.1 1.41 0.33 0.22 0.44 Clay

a

According to the Harmonized World Soil Database (Nachtergaele and Batjes 2012)

b Field measured parameter from the International Center for Agricultural Research in the Dry Areas (ICARDA) (unpublished data)

Datasets and stream parameters In this study, daily streamflow (discharge) and stage measurements were used to estimate different hydrological parameters of Al Qweek River and Al Qwaak channel. The data were observed hourly by three gauge stations located in the region and cover the period from 2002 to 2006. The gauge stations of Al Wdehi and Kurrasi are located at the Al Qweek River; only one station was installed at the Al Qwaak ephemeral channel (Al Zerba station). These stations were established as a consequence of the cooperation between the Syrian Ministry of Irrigation (MOI) and the BGR for the purpose of water resource development of the Aleppo basin. The main important morphological and hydrological characteristics of the streams at measuring stations are shown in Table 2. In addition to the river data, daily precipitation data were obtained from an Aleppo reference weather station. Furthermore, monthly groundwater tables in three observation wells (R161, R136, and C1B) located close to the river were used to interpret the seasonal changes and the relative potential relationship between the water table in the region and changes in river stage

Author's personal copy Arab J Geosci Table 2 Hydrological properties of the Al Qweek and Al Qwaak rivers at the location of the observation gauge stations

Station

Al Wdehi

Kurrasi

Al Zerba

Location

36° 5′ 54.04″ N

36° 5′ 56.40″ N

36° 3′ 5.74″ N

Elevation (m) River width (m) Avg. river slope (%) Avg. water depth (cm) Avg. discharge (m3/s) Avg. EC (μS/cm) River bed soil texture (%)a

37° 7′ 30.47″ E 340 12.95 1.5 24 5.44 1385 Sand Silt

Clay

37° 4′ 57.70″ E 300 11.54 2 41 3.61 1363 Sand Silt

Clay

36° 57′ 10.57″ E 272 5.89 0.5 17 0.34 1297 NA

51.42

23.82

51.42

Hydraulic conductivity (m/day)

23.82 0.029

24.76

24.76

NA NA

NA no data available According to Sato (2010)

36°53'0"E

36°58'30"E

37°4'0"E

37°9'30"E

36°13'30"N

36°47'30"E

hydraulic properties of the riverbed were drawn from published and unpublished government reports.

River

Aleppo

lQ

A

36°8'0"N

Al Qweek

Airport station

k

aa

w

R136

an

ch

R161

36°2'30"N

l

ne

Kurrasi

36°13'30"N

over the modeled years. Figure 5 shows the locations of the gauge stations and observation wells. Soil texture and

36°8'0"N

a

Al Wdehi

36°2'30"N

Al Zerba C1B

Tel Hadya

Legend Weather station

35°57'0"N

River gauge station

River Catchment

Al Matah 36°47'30"E

0

2.5

5

36°53'0"E

10

15

36°58'30"E

20 Km

Fig. 5 The locations of weather/river gauge stations and observation wells

37°4'0"E

37°9'30"E

35°57'0"N

Observation well


Hydrograph analysis The mechanism of groundwater/surface water exchange was investigated using hydrograph analysis techniques of daily river discharge data. These methods can be used to identify portions of streamflow that can be attributed to surface runoff or groundwater discharge as well as infiltration into the groundwater. In this study, three different techniques were used as described below. Base-flow separation

N ¼ 0:83A0:2 ;

ð2Þ

where N is the number of days and A is the area of drainage surface in square kilometers. The fixed interval method assigns the lowest discharge rate within the interval time 2N*. The method can be visualized by moving a bar 2N* upward until the bar intersects the hydrograph. For the sliding interval method, base flow is set equal to the lowest daily discharge within an interval extending by 0.5(2N*−1)days before and after the selected time. The local minima method uses the lowest discharge rate at 0.5(2N*−1)days before and after the

mb

crest point

b

Lim

Risin

g Li

ling

Fal

Fig. 6 Schematic showing the manual hydrograph separation; the drawn tangent line at the recession point B will intersect the hydrograph peak at point C. A is the point of initial rise on the hydrograph. The segment between the connected line between A, C, B, and the time axis represents the base flow, while the upper one is the quickflow area (Brodie and Hostetler 2005)

Discharge

Many methods have been developed to quantify base flow or groundwater recharge of the total flow; these include the empirical manual separation methods and automatic continuous hydrograph separation (Fig. 6). The continuous separation techniques serve to sub-divided a time-series record of a stream discharge into quickflow as direct response to a rainfall event (over land runoff/interflow) and base flow as a longterm discharge of natural storage or delayed flow (Hall 1968; Nathan and McMahon 1990; Brodie and Hostetler 2005). Various types of important information about the dynamic behaviors of groundwater of a catchment can be derived from the base-flow analysis. For instance, the base-flow index (BFI) as a ratio of base flow to the total flow provides valuable information about the ability of a catchment to store or release water during the dry season. The index is dimensionless and ranges from 0 to 1. A high BFI index refers to a relatively stable flow regime and thus high river sustainability during dry periods (Tallaksen 1995).

However, base-flow indices are highly correlated to the hydrological properties of soil and geological formations of the catchment (Gregor 2010). In this study, automatic separation of daily discharge data was carried out using the HydroOffice and BFI+ software package for water sciences and base-flow analysis developed by Gregor (2010); the software is available for free to download (http://www.hydrooffice.org). The BFI+ package was utilized for analysis and separation of base flow using 11 types of filters. Four digital filter techniques were used in this study: the fixed interval method, sliding interval method, and local minimum method described by Sloto and Crouse (1996), which is already integrated in the HYSEP computer program (http://water.usgs.gov/software/HYSEP/). In addition, the digital filter implemented in BFLOW (Lyne and Hollick 1979) was used. The most important step before applying filters to the time series is to estimate the number of days N, which represent the point along the falling limb of the hydrograph and all of the streamflow is base flow. N was approximated for the region by using the following empirical equation (Linsley et al. 1982):

Quickflow

A

C

Baseflow

B

Time


day being considered and connected by straight lines representing the base flow. These filters are described in detail by Sloto and Crouse (1996). The BFLOW filter on the other hand is a recursive digital filter which uses the advantage of signal processing techniques to remove high-frequency quickflow in order to derive the low-frequency base flow. The parameter filtering equation is given by 1þα Q f ðiÞ ¼ ∝Q f ði−1Þ þ QðiÞ −Qði−1Þ ð3Þ 2 where Qf(i) is the filtered quickflow for the ith sampling instant (the value is ≥0), Q(i) is the original streamflow for the ith sampling instant, Q(i−1) is the streamflow of the pervious sampling instant, and α is a filter parameter (a value of 0.925 is recommended for reasonable results of daily stream data (Arnold et al. 1995)). All these filters were used to estimate the base flow and BFI. Generally, the value of BFI can range from 0.15 for impermeable catchments with a flashy flow regime, and 0.9 for permeable catchment with a relatively stable flow regime (Tallaksen and Van Lanen 2004). Streams that are not connected to an aquifer could have a BFI of 0 (Winter 1999). Furthermore, the groundwater recharge can be estimated based on the water budget for an aquifer using the following equation (Healy and Scanlon 2010): gw R ¼ ΔS þ Qb f þ ETgw þ Qgw ð4Þ out −Qin where R is the groundwater recharge, ΔS is the change in groundwater storage, and ETgw is the evapotranspiration from shallow groundwater. (Qgwout −Qgwin) is the groundwater discharge of an aquifer and comprises pumping and inter-aquifer flow. The ET from groundwater in arid and semi-arid regions with a relatively deep water table is assumed to be equal to 0 (the average groundwater depth in the study area is about 90 m). Assuming that all parameters on the right side of Eq. 4 except base flow Qbf are negligible (closed basin, no exchange of water with underlying horizons, and no significant change in aquifer storage), then groundwater recharge is relatively equal to the base flow (Healy and Scanlon 2010): R≈Qb f

surface/groundwater relationship. Streamflow duration curves describe the relationship between magnitude and frequency of occurrence of daily, weekly, and monthly recorded stream discharge. These curves are very important in the study of flow regimes in a catchment. They provide qualitative information about the streamflow and its relationship to the groundwater by interpreting the shape of the flow duration curves (FDC). The goal is to sort flow values in descending form, then to give a rank for each flow value starting with 1 for the highest flow and increasing so on to N for the lowest flow value. The probability of distribution of the time series was calculated using the following formula: m P ¼ 100 ð6Þ N þ1 where m is the rank of the specific discharge value. The flow probability as flow percentage is presented on a log-normal plot to provide detailed information about low-flow values. A steep slope of a duration curve indicates dominating surface flow (surface runoff), while a low gentle slope suggests base flow or groundwater discharge (Healy and Scanlon 2010). The shape of the duration curve in its upper and lower parts shows the characteristics of the perennial storage in the drainage basin, so that a flat curve at the lower point indicates a high storage value and vice versa (Searcy 1959). The discharge value, which is equal to or exceeds 50 % of the time (Q50), represents the lowflow period of the river discharge. Various indices of low flow have been developed to characterize the variability of base flow such as Q90/Q50 to indicate the groundwater storage contribution (Nathan and McMahon 1990); the log(Q50/Q90) index was suggested by Nelms et al. (1997). A low index value represents less base-flow variability, which indicates sustained base-flow discharge over time as a response of increased groundwater storage. In this study, yearly and master flow duration curves (MFDC) are generated flow discharge of the three gauge stations for the period 2002–2006. The FDC were constructed using discharge data observed daily and developed using the FDC v 2.1 package integrated in HydroOffice. The low-flow variability index of Q50/Q90 was used to characterize the streamflow within Al Zerba catchment.

ð5Þ

After the complete separation of daily discharge data of the three gauge stations, base-flow data were compared together as well as their contribution to the total flow for the modeled period. The average monthly BFI was used to characterize the relationship between surface and groundwater.

Streamflow duration curves (frequency analysis) Frequency duration curves of the gauge stations were used to characterize base flow and low-flow period as well as the

Recession curve displacement analysis The recession curve (RC) is a specific portion of the hydrograph after crest point where streamflow depletes. The method of RC displacement is a well-known technique in hydrography analysis. It is based on the assumption that recharge and rises in stream stage occur only in response to the rainfall events in late fall and winter when evapotranspiration is low (Healy and Scanlon 2010). The RC displacement method was described by Rorabaugh (1964) as a one-dimensional flow model; the author suggested the equation of the recession


index K as a function of aquifer hydraulic properties as shown below: 0:196S y a2 Tc ¼ ¼ 0:2114 K ð7Þ T where Tc is the critical time where the recession curve becomes linear (hydrograph falling time), T is the aquifer transmissivity, Sy is the aquifer specific yield, and a is the distance from the stream to the aquifer boundary. The recession index can be estimated manually (graphical method) or by using computer programs such as RECESS (Rutledge 1998). This recession index serves to estimate the net groundwater recharge from the following equation: 2ðQ2 −Q1 Þ K ð8Þ 2:3026 where Q1 and Q2 are the base flow at the critical time (Tc) after and before the peak rises and K is the recession index computed from the hydrograph analysis. R is the net groundwater recharge. Four main steps can summarize the estimation of groundwater recharge using the RC displacement: (1) computing the recession index; (2) calculating the critical time applying Eq. 7; (3) using the critical time to delineate Q1 and Q2; and (4) the estimation of the total groundwater recharge according to Eq. 8. These steps have been integrated into the computer program RORA (Rutledge 1998). This program was used to analyze R¼

Fig. 7 Flowchart of the recession curves analysis using RC v 4.0 program in HydroOffice

ground and surface water exchange by diffuse recharge to the water table and base flow to a stream (Rutledge 2007). Both RORA and RECESS were used in the study for the estimation of groundwater recharge. However, RORA may not provide reasonable estimation of groundwater discharge in aquifers with heterogeneous recharge, because of simplified assumptions in the recharge equation (Eq. 8) (Halford and Mayer 2000). One other important application of the recession analysis is to indicate the surface/groundwater relationship based on the K index. A higher K value indicates a sustained dominant base flow. Generally, K values ranging between 0.2 and 0.8 are typical for runoff, 0.8 and 0.94 for interflow, and 0.93 and 0.995 for the base flow (Nathan and McMahon 1990). In this study, the RC v 4.0 package program, integrated in HydroOffice (Gregor 2010), was used for complex processing and analysis of the RC of daily discharge data of the gauge stations. The program enables calibration of the RCs as well as the master recession curve (MRC) using various recession functions to fit the reservoir and runoff model. Gregor and Malík (2012) published a new method for automated delineation of the MRC. This method is based on a combination of a strong hybridized genetic algorithm method and an artificial immune system (GA algorithm) method. However, the RCs of the gauge stations were selected manually using the selection tool of the RC program. The data of each individual curve were reviewed

Author's personal copy Arab J Geosci Fig. 8 Monthly river and groundwater head fluctuation with catchment area for the period 2002–2006


and interpolated in order to remove abnormal reaches. After that, the recession index K was computed to fit the selected curve to the optimal recession model. This procedure is illustrated in Fig. 7. RORA and RECESS were used together under the DOS environment to estimate the net groundwater recharge using information from the recession curve analysis. Hence, it was not included into the flowchart. The MRC of selected segments of the RCs was used to characterize the base-flow response and aquifer flow regime within the catchment area.

Results and discussion Potential surface/groundwater relationship The visual inspection of the monthly fluctuation of Al Qweek and Al Qwaak rivers in comparison to the groundwater head indicates a proportional relationship with lag-time ranges between 2 and 3 months at Al Wdehi and Kurrasi stations and 1 and 2 months for Al Zerba (Fig. 8). This can be explained by

Fig. 9 Fluctuation in river discharge and average daily precipitation of the gauge stations during the period 2002–2006


both direct and indirect impacts of the various factors such as the infiltration time of surface water down through the

unsaturated zone to the groundwater table, variation in the hydraulic properties of the sub-surface layers, as well as the

Fig. 10 Hydrograph/base-flow separation of the gauge stations using four different filters

Author's personal copy Arab J Geosci Table 3 Base-flow contribution (%) of the total flow separated using four different filters

Station

Year

Local minima

Fixed interval

Sliding interval

BFLOW

Average

Al Wdehi

2002 2003 2004 2005 2006

87.16 74.41 85.11 78.46 72.93

91.03 84.48 87.07 85.33 84.69

92.22 87.15 87.07 87.27 82.79

94.93 92.17 93.21 92.94 91.40

91.34 84.55 88.12 86.00 82.95

Average St. dev 2002 2003 2004 2005 2006 Average St. dev 2002 2003 2004 2005 2006 Average St. dev

97.61 6.33 80.14 76.19 78.15 81.95 73.50 77.99 3.31 79.10 75.45 71.32 90.04 86.36 80.45 7.70

86.52 2.72 85.71 83.10 83.96 87.30 85.73 85.16 1.65 86.65 81.23 90.50 94.64 93.16 89.24 5.41

87.30 3.34 88.81 86.69 86.26 89.99 88.84 88.12 1.58 88.14 85.73 92.00 96.73 94.39 91.40 4.48

92.93 1.32 92.91 91.24 92.57 94.27 93.95 92.99 1.21 87.22 89.03 93.83 94.68 94.99 91.95 3.58

86.59 3.26 86.89 84.30 85.24 88.38 85.50 86.06 1.59 85.28 82.86 86.91 94.02 92.23 88.26 4.71

Kurrasi

Al Zerba

groundwater depth. Moreover, the distance between the observation wells and gauge stations is an important factor as argued by Zucker et al. (1973). Considering the onedimensional Boussinesq equation, the change in groundwater storage under steady-state conditions is inversely proportional to the distance from the river. As distance from the river increases, the response of groundwater to the changes in river stage becomes lower, so that the flow paths are longer and deeper (Tucci and Hileman 1992; Alley et al. 1999). However, these proportional changes provide potential evidence about the connection between surface water of the rivers

Table 4 Monthly average and standard deviation of the BFI using different separation methods at the three gauge stations

Station Al Wdehi

Kurrasi

Al Zerba

Min Max Monthly avg. St. dev Min Max Monthly avg. St. dev Min Max Monthly avg. St. dev

and shallow upper aquifers in the region. Considering the amount of rainfall, a significant relation was found between the river discharge and precipitation and thus with the groundwater table (Fig. 9). Disparities in some parts of the discharge time series can be explained by the amount of water involved in surface runoff, and time to reach the river channel from drainage areas. Furthermore, the fact that the Aleppo meteorological station (in the east) was located relatively far from the observation site, while Al Zerba river gauge station is close to the Tel Hadya weather station, must be taken into consideration. Generally, the water table is at the lowest level during the dry season/late fall (mid-

Local minima

Fixed interval

Sliding interval

BFLOW

0.57 0.94 0.82 0.07 0.63 0.93 0.81 0.06 0.54 1.00 0.85 0.10

0.71 0.96 0.88 0.04 0.73 0.95 0.87 0.03 0.44 0.99 0.89 0.09

0.80 0.97 0.90 0.03 0.81 0.97 0.90 0.03 0.10 1.00 0.88 0.16

0.88 0.98 0.95 0.02 0.81 0.99 0.95 0.02 0.54 1.00 0.92 0.08


Fig. 11 Annual and master base-flow duration curves of Al Qweek River and Al Qwaak River


Fig. 12 Master recession curves of the three gauge stations show a linear model to describe the overland flow and groundwater storage


Fig. 13 Monthly groundwater recharge estimated using RORA program at the gauge stations

September and October) while the rising river stage at these times can result from groundwater discharging into Al Qweek River as base flow. In contrast to the ephemeral Al Qwaak River, it dries up in the summer until the early fall because of significant decrease in reaches from the drainage areas and tributaries. At this stage, surface water seems to recharge the aquifer. Base flow and FDC analysis Results of base-flow and total flow components of the daily discharge data for the Al Qweek and Al Qwaak rivers during Table 5 Estimated net groundwater recharge using RORA

the period 2002–2006 are shown in Fig. 10. It presents baseflow fluctuation of the three gauge stations separated using the local minima, fixed interval, sliding interval, and BFLOW methods. The results indicate a dominant base flow in the region with an average annual contribution of the base flow of 86.3 % of the total flow for the Al Wdehi and Kurrasi gauge stations (Table 3). The average annual estimated base-flow contribution from the Al Qwaak Ephemeral River at the Al Zerba gauge station was 88.3 % of the total flow. All the four separation methods provided relatively convergent results of the base-flow proportion except the local minima method

Station ID

Al Wdehi

Kurrasi

Al Zerba

Drainage area (km2) K index (days/log cycle) Al Wdehi Quarter recharge in mm

Year Jan–Mar Apr–Jun Jul–Sep Oct–Dec Quarter avg. Jan–Mar Apr–Jun

249.97 20.61 2002 – – 39.37 42.41 20.44 – –

2003 69.85 73.15 34.03 52.57 57.40 21.33 26.92

273.89 22.71 2004 80.01 71.37 40.38 39.87 57.91 97.02 56.38

505.20 26.88 2005 105.15 73.91 42.16 115.57 84.20 62.99 41.65

2006 67.81 23.62 63.50 60.45 53.84 96.01 40.89

Jul–Sep Oct–Dec Quarter avg. Jan–Mar Apr–Jun Jul–Sep Oct–Dec Quarter avg.

2.28 16.76 4.76 14.98 – – – 3.61

12.95 38.35 24.89 7.87 1.52 0.00 5.08 3.61

14.47 30.48 49.59 7.87 3.04 2.28 5.58 4.69

11.43 39.87 38.98 4.06 0.76 0.00 6.60 2.85

55.62 101.85 73.59 16.76 0.00 0.00 2.03 4.69

Kurrasi

Al Zerba


(Table 3). The table shows a relative decrease of base flow in some years for the Al Wdehi and Kurrasi stations. This can be explained by a potential clogging of the riverbed after a large load of suspended fine sediment through high flow, particularly in mid-February and early spring. Considering the riverbed soil texture as shown in Table 2, the fine-grained riverbed can have adverse effects on the infiltration capacity of the Al Qweek alluvial system. According to base-flow results, the computed mean annual BFI ranged from 0.85 to 0.90 in all gauged stations indicating permeable conditions of the catchment area with a stable flow regime associated with a high percentage of the base flow and lower direct surface runoff (Table 4). From the perspective of statistics, the BFLOW method gave more consistent results than the other three methods as the least value of standard deviation ranged from 0.02 to 0.04. In addition to the base-flow separation technique, the results achieved using the FDC method exhibited low sloping duration curves suggesting a high contribution of the base flow of the total flow resulting in a uniform flow sustained by groundwater storage (basin-storage discharge). Moreover, the steep slopes of the lower end of the duration curves in some years indicate a negligible amount of perennial storage in the drainage area (the years 2004 and 2005). It seems also that Al Qwaak Ephemeral River in some years (2005 and 2006) is dominated by surface flow with little or no groundwater discharge where the streamflow diminishes in the absence of the focused recharge. Furthermore, the low-flow index (Q 90 /Q 50 ) indicates the proportion of groundwater storage of 4.7 to 43 % for the Al Qwaak River and 45 to 58 % for the Al Qweek River. Figure 11 shows the annual and master duration curves obtained from the daily flow data. However, the region can be characterized by a low to medium flow system and low base-flow variability. The average slope of the duration curves ranged from 0.006 to 0.01 for the Al Zerba station and 0.04 to 0.05 for the Al Wdehi and Kurrasi stations. RCs analysis and groundwater recharge The analysis of flow RCs over 5 years shows 31 and 21 selected curves for Al Qweek River at the Al Wdehi and Kurrasi gauge stations, respectively. In contrast, only 14 RCs were found on Al Qwaak River. The flow range of the RCs varied from 0.1 to 33.7 m3/s at the catchment inlet, while a significantly lower flow range was observed on the Al Qwaak River with a maximum flow of 1.85 m3/s for the RCs. The recession function of the RCs was simulated by a linear reservoir model to describe the general storage over a short time period. This model is based on the linearized Depuit–Boussinesq equation derived by Boussinesq (1877). The average estimated recession constant (K) was 0.92 at the Al Wdehi and Kurrasi stations. According to Nathan and McMahon (1990), this value describes a temporary interflow

after storm periods followed by sustained base flow from the banks. Conversely, Al Qwaak River presents lower recession constant ranges from 0.70 to 0.88 indicating a dominant interflow and low overland runoff. This can be clearly deduced from the MRCs of both rivers as shown in Fig. 12. Almost the same amount of base flow can be observed in the Al Wdehi and Kurrasi stations except for the overland runoff, which seems to be higher at the catchment inlet in comparison to other parts of the river. Steep topographic slopes and lower vegetation cover in the drainage area can explain this issue. On the other hand, Al Zerba station on Al Qwaak River shows significantly low overland flow with dominant interflow and groundwater storage. The results also indicate that groundwater recharge into the shallow Quaternary and Helvetian aquifers occurs mainly during the winter and late spring and early fall with an average annual groundwater recharge ranging from 188.51 to 16.00 mm/year for Al Qweek River and Al Qwaak River, respectively. The results of monthly groundwater recharge modeled in the RORA are shown in Fig. 13. In fact, the amount of water sustained in the upper aquifer was overestimated for the Al Qweek River and is inconsistent in comparison to previous studies in the region conducted by Selkhozpromexport (1979), UNESCWA (1997), Luijendijk and Bruggeman (2008), and most recently by Abo and Merkel (2015), which indicate annual groundwater recharge ranging from 20 to 60 mm/ year. Unlike this, a more reasonable net groundwater recharge value was obtained for Al Qwaak River in the southwestern part of the catchment. Table 5 presents the quarter net groundwater recharge estimated from the RC displacement method.

Conclusion and recommendations The results indicate interaction between surface and groundwater reflecting high water exchange either by base flow or focused net groundwater recharge. Surface runoff is higher in the upstream of Al Qweek River since the drainage area is close to the river with a higher average slope. The high BFI of both rivers results in relatively high permeability of the catchment and lower overland flow and high contribution of base flow to the total flow. The results of the low-flow index as well as low slopes of the FDC showed sustained baseflow from groundwater storage. Net groundwater recharge from an analysis of RCs seems to be an unsuitable method for the region. Despite that, important indicators about surface water infiltration in the region are provided; these results were consistent with the results of base-flow separation. Finally, it is highly recommended to verify these results using chemical and isotopic streamflow analysis and a tracer test in the future.

Author's personal copy Arab J Geosci Acknowledgments The authors would like to thank Dr. Adriana Bruggeman for the helpful suggestions. Special thanks are due to Dr. Milos Gregor for his technical assistance and the Syrian Ministry of Water Resource for providing us with required data. The authors thank the hydrogeology staff in the Department of Geology at the TU Freiberg for their appreciated support. We give thanks to two anonymous reviewers for their suggestions to improve the paper.

References Abo R, Merkel B (2015) Comparative estimation of the potential groundwater recharge in Al Zerba catchment of Aleppo basin, Syria. Arab J Geosci 8(3):1339–1360. doi:10.1007/s12517-013-1222-9 ACSAD (1985) Soil map of Arab countries, soil map of Syria & Lebanon 1:1000.000. The Arab Center for the Studies of Arid Zones and Dry Lands (ACSAD), Damascus Aksoy H, Wittenberg H (2011) Nonlinear base-flow recession analysis in watersheds with intermittent streamflow. Hydrol Sci J J Sci Hydrol 56(2):226–237 Al-Charideh A (2012) Geochemical and isotopic characterization of groundwater from shallow and deep limestone aquifers system of Aleppo basin (north Syria). Environ Earth Sci 65(4):1157–1168 Alley WM, Reilly TE, Franke OL (1999) Sustainability of ground-water resources. US Department of the Interior, US Geological Survey Circular 1186, Colorado Appleby FV (1970) Recession and the base-flow problem. Water Resour Res 6(5):1398–1403 Arnold JG, Allen PM (1999) Automated methods for estimating baseflow and ground water recharge from streamflow records. JAWRA J Am Water Resour Assoc 35(2):411–424. doi:10.1111/j.1752-1688. 1999.tb03599.x Arnold JG, Allen PM, Muttiah R, Bernhardt G (1995) Automated base flow separation and recession analysis techniques. Groundwater 33(6):1010–1018 Asfahani J, Radwan Y (2007) Tectonic evolution and hydrogeological characteristics of the Khanaser valley, northern Syria, derived from the interpretation of vertical electrical soundings. Pure Appl Geophys 164(11):2291–2311 BGR, MOI (2004) Initial assessment study of water sector management in the Syrian Arab Republic. Federal Institute for Geosciences and Natural. Resources & Syrian Ministry of Irrigation, Damascus Boussinesq (1877) Essai sur la theories des eaux courantes. Memoires presentes par divers savants a l‘Academic des Sciences de l‘Institut National de France Tome XXIII, No 1 Boussinesq J (1904) Recherches théoriques sur l’écoulement des nappes d’eau infiltrées dans le sol et sur le débit des sources. J Math Pures Appl:5-78 Brew G, Barazangi M, Al-Maleh AK, Sawaf T (2001) Tectonic and geologic evolution of Syria. Geoarabia-Manama 6:573–616 Brodie R, Hostetler S (2005) A review of techniques for analysing baseflow from stream hydrographs. In: Proceedings of the NZHS-IAHNZSSS 2005 Conference Calver A (2001) Riverbed permeabilities: information from pooled data. Ground Water 39(4):546–553 CBS (2011) Statistical abstract 2011, Chapter 4: agriculture. The Syrian Central Bureau of Statistics, Damascus Charlton R (2007) Fundamentals of fluvial geomorphology, vol 32. Routledge, London FAO (2008) AQUSTAT Report of the Syrian Arab Republic (water report 34). Food and Agriculture Organization of the United Nations (FAO), Rome Freeze RA, Cherry JA (1979) Groundwater, 1979. Prentice Hall, New Jersey

GCHS (1999) Updating study of Aleppo basin within Syrian territories (tables of water exploitation for different uses). General Company of Hydraulic Studies (GCHS), Homs, Syria Gee GW, Hillel D (1988) Groundwater recharge in arid regions: review and critique of estimation methods. Hydrol Process 2(3):255–266 Gregor M (2010) User manual for BFI+ 3.0. http://www.hydrooffice.org/ Downloads/List.aspx?section=Manuals Gregor M, Malík P (2012) Construction of master recession curve using genetic algorithms. J Hydrol Hydromech 60(1):3–15 Gruzgiprovodkhoz (1982) Hydrogeological and hydrological surveys and investigations in four areas of the Syrian Arab Republic. Georgian State Institute for Design of Water Resources, Tbilisi Halford KJ, Mayer GC (2000) Problems associated with estimating ground water discharge and recharge from stream-discharge records. Ground Water 38(3):331–342 Hall FR (1968) Base‐flow recessions—a review. Water Resour Res 4(5):973–983 Hamdy A, Abu-Zeid M, Lacirignola C (1995) Water crisis in the Mediterranean: agricultural water demand management. Water Int 20(4):176–187 Healy RW, Scanlon BR (2010) Estimating groundwater recharge (vol 237). Cambridge University Press, Cambridge JICA (1997) The study on water resource development in the northwestern and central basin in the Syrian Arab Republic (phase 1). Sanyu Consultants Inc, Tokyo Linsley RK, Kohler MA, Paulhus JL (1982) Hydrology for engineers, 3rd edn. McGraw-Hill, New York Luijendijk E (2003) Groundwater resources of the Aleppo basin, Syria. MSc Thesis, Vrije Universiteit Amsterdam, The Netherlands Luijendijk E, Bruggeman A (2008) Groundwater resources in the Jabal Al Hass region, northwest Syria: an assessment of past use and future potential. Hydrogeol J 16(3):511–530 Lyne V, Hollick M (1979) Stochastic time-variable rainfall-runoff modelling. In: Institute of Engineers Australia National Conference, pp 89-92 Martin (1999) Water availability and water use in Syria. Report for the World Bank, Washington, DC Nachtergaele F, Batjes N (2012) Harmonized world soil database (ver 1.2). FAO and IIASA, Rome Nathan R, McMahon T (1990) Evaluation of automated techniques for base flow and recession analyses. Water Resour Res 26(7):1465–1473 Nelms DL, Harlow GE, Hayes DC (1997) Base-flow characteristics of streams in the Valley and Ridge, Blue Ridge, and Piedmont Physiographic Provinces of Virginia (paper 2457). US geological survey, Denver Petts G, Amoros C (1996) The fluvial hydrosystem. Chapman and Hall, London Ponikarov VP (1964) Geological map of Syria, scale 1:200,000. Technoexport, Moscow Qian K, Wan L, Wang X, Lv J, Liang S (2012) Periodical characteristics of base-flow in the source region of the Yangtze River. J Arid Land 4(2):113–122 Rantz S (1982) Measurement and computation of streamflow. U S Geol Surv Water Supply Pap 2175:631 Rorabaugh M (1964) Estimating changes in bank storage and groundwater contribution to streamflow. Int Assoc Sci Hydrol 63:432–441 Rouhani H, Malekian A (2013) Automated methods for estimating baseflow from streamflow records in a semi arid watershed. Desert 17(2):203–209 Rutledge AT (1998) Computer programs for describing the recession of ground-water discharge and for estimating mean ground-water recharge and discharge from streamflow records: update. US Department of the Interior, US Geological Survey water resource, Rep 98-4148 Rutledge AT (2007) Update on the use of the RORA program for recharge estimation. Groundwater 45(3):374–382

Author's personal copy Arab J Geosci Ryan J, Masri S (1997) Soils of ICARDA’s agricultural experimental stations and sites: climate, classification, physical and chemical properties, and land use. ICARDA, Aleppo Sato T (2010) Sustainable management of saline waters and salt-affected soils for agriculture: proceedings of the Second Bridging Workshop Nov 2009. In. International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria pp 73-78 Scanlon BR, Healy RW, Cook PG (2002) Choosing appropriate techniques for quantifying groundwater recharge. Hydrogeol J 10(1):18–39 Schälchli U (1992) The clogging of coarse gravel riverbeds by fine sediment. Hydrobiologia 235–236(1):189–197 Searcy JK (1959) Flow-duration curves. US Geological survey water supply paper 1542-A. U.S. Geological survey Washington, DC Seiler KP, Gat JR (2007) Groundwater recharge from run-off, infiltration and percolation (vol 55). Water Science and Technology Library. Springer Dordrecht, Netherlands Selkhozpromexport (1979) Hydrogeological and hydrological survey and investigation in four areas of Syrian Arab Republic (vol 2). Tiflis, Georgia Simmers I (1988) Estimation of natural groundwater recharge (vol 222). Springer Sloto RA, Crouse MY (1996) HYSEP, a computer program for streamflow hydrograph separation and analysis. US Geological survey water supply. U.S. Geological survey, Washington, DC Smakhtin V (2001) Low flow hydrology: a review. J Hydrol 240(3):147–186 Stadler S, Geyh M, Ploethner D, Koeniger P (2012) The deep Cretaceous aquifer in the Aleppo and Steppe basins of Syria: assessment of the meteoric origin and geographic source of the groundwater. Hydrogeol J 20(6):1007–1026 Starkel L (1995) Changes of river channels in Europe during the Holocene. Changing river channels. Wiley, Chichester, pp 27–42 Tallaksen LM (1995) A review of base-flow recession analysis. J Hydrol 165(1):349–370

Tallaksen LM, Van Lanen HA (2004) Hydrological drought: processes and estimation methods for streamflow and groundwater (vol 48). Elsevier B.V, The Netherlands Tucci P, Hileman GE (1992) Potential effects of dredging the South Fork Obion River on ground-water levels near Sidonia, Weakley County, Tennessee. US Department of the Interior, US Geological Survey, Water-Resources Investigations Report 90-4041., Nashville, Tennessee UNEP (1997) World atlas of desertification. Edward Arnold, London UN-ESCWA (1997) Report on mission to Syrian Arab Republic (during the period 10-20 Jun 1997). Hydrogeologic advice to ICARDA on sustainable agricultural groundwater managment in dry areas. Beirut Wagner W (1997) Report on mission to the Syrian Arab Republic: hydrogeologic advice to ICARDA on sustainable agricultural groundwater management in dry areas. ESCWA, Amman Welderufael W, Woyessa Y (2010) Stream flow analysis and comparison of base flow separation methods: case study of the Modder River basin in Central South Africa. Eur Water 31:3–12 Winter TC (1999) Ground water and surface water: a single resource (vol 1139). DIANE Publishing Wolfart R (1966) Zur Geologie und Hydrogeologie von Syrien: unter besonderer Berücksichtigung der süd-und nordwestlichen Landesteile [On the geology and hydrogeology of Syria, with special reference to the southern and northwestern regions of the country]. Bundesanstalt f. Bodenforschung, Hanover Xu Y, Beekman HE (2003) Groundwater recharge estimation in Southern Africa. UNESCO, Paris Zucker MB, Remson I, Janet E, Aguado E (1973) Hydrologic studies using the Boussinesq equation with recharge term. Water Resour Res 9(3):586–592