Surface water resources management along Hadejia River Basin, northwestern Nigeria

The current review has unveiled the spatial disparity of the surface water resources availability between the upstream and downstream of the Hadejia River Basin (HRB). The surface water resources are more abundant in the upstream areas of the basin. Although rainfall and temperature dynamics are identi ﬁ ed as the major reason for these spatial variations, other important factors include the differences in the geological formation and the land use changes. Furthermore, the differences in the geological formations between the upstream and downstream areas have further widened the disparities in the surface water resources available across the basin which are motivated by the differences in the rate of in ﬁ ltration. The combined effects of these factors affect both spatial availability and the quality variation of the surface water resources. However, as per this review, there is no single integrated study reported to have aimed at addressing the problems of water resource excesses, de ﬁ ciencies and/or pollution throughout the basin. To address the problem of water pollution, ﬂ oods, and droughts, the current review recommends the use of riverbank ﬁ ltration (RBF), aquifer recharge and recovery (ARR) and rainwater harvesting.


INTRODUCTION
Water is significant to life, it is the next important resource after oxygen and this makes it indispensable in all aspects of human endeavour (Ahmadi & Moradkhani 2019;Falkenmark 2013). For this reason, it is deemed important for any meaningful sustainable development initiatives. In drier regions of the world (like the case at hand), rainfall unreliability and the resultant surface water insufficiencies have necessitated groundwater exploration despite huge investment (Abdulhamid 2014;Mehra et al. 2016). In view of this increasing surface water resources predicament, a substantial number of people living in sub-Saharan Africa are gradually shifting to groundwater sources for a potable water supply (Kumar et al. 2007). Instances were reported from many African countries mean annual flow, peak flow and mean date of peak flow are 1,396 mm 3 /s to 43 mm 3 /s, 597 mm 3 /s to 38 mm 3 /s, and 10 August and 16 September between the upstream and downstream areas of the basin .
The area is known for temporal and spatial variations in rainfall. Annual mean rainfall is about 600 mm in the northeastern parts to 800 mm in the midstream area to 1,000 mm in the extreme south of the basin. Generally, wet periods last between four, five and six months in the extreme north, midstream and the extreme south of the basin, respectively. Consequently, the basin experiences dryness in the rest of the months of the year. Geologically, the basin is underlain by two main geological configurations divided by a boundary (Figure 2(a)). The southern portion of the geological divide is covered by basement complex geological structure of igneous origin, while the   northeastern portions of the basin are covered by sedimentary Chad formation (Figure 2(a)). The basement complex structure consists of the comparatively shallow weathered mantle on top of solid igneous rocks which hinders surface water penetration. In tune with geological variation, the soil of the area is similarly varied from south to the north of the basin even though it is dominated by a sandy soil fraction (Figure 2(b)). This soil disparity has also contributed to the determination of the rate of infiltration and thus surface and groundwater potentials in the region. However, the Chad formation sedimentary rocks are made up of unconsolidated sediments. Moreover, there exist deposits of alluvial materials on top of river floodplains that are less difficult to exploit for groundwater exploration using tube wells. Therefore, these main geological structures of the basin were found to influence the spatial availability of surface and groundwater as well as the quality of the waters in the basin. Thus, there is a clear spatial disparity of surface water availability between the two geological formations, with the Chad formation structural region having more groundwater resources and the basement complex region being relatively advantageous in terms of surface water resources availability (Thompson & Polet 2000). Generally, water resources management strategies are essentially scanty. The downstream areas of the basin are currently under pressure and the available groundwater is severely exploited due to the insufficient surface water resources. Additionally, the dominant land use type of the basin is agriculture (Figure 2(c)), which is practised in both rain-fed and irrigated bases. To the south of the basin is higher elevation and the northern part of the basin is dominantly of lower relief (Figure 2(d)).

Method
An extensive literature survey forms the basis of this study, thus a bibliographic review was based on index citation from various internet sources such as Google scholar citation index and the science citation index expanded (SCIE) databases. This has enabled the evaluation of surface water-related research in the region, handling various issues and viewpoints (Table 1). The studies conducted in this basin profile were mostly related to the impact of river regulation on the river discharge fluctuations in the Hadejia Nguru Wetland (HNWL). Consequently, about 60% of the studies conducted in the entire basin were in the downstream area. Moreover, the downstream area is economically and recreationally important for supporting the flood recession agriculture and hosting the internationally recognized RAMSAR site that accommodates different species of migratory birds.

Water resource management
A river basin is a physiographic unit composed of interrelated parts and functions. The same geomorphological unit is referred to as a drainage basin, a catchment or a watershed. In a more simple explanation, a river basin comprises the area drained by a river and its tributaries. It provides a convenient natural area within which hydro-meteorological data can be collected and synthesized, from which, other physical and detailed hydrological processes can be meaningfully studied. The fact that its boundaries are stable and well defined is considered and adopted as a convenient spatial unit for water resource development planning (Ayoade 1988). The approach to and strategy for river basin development have undergone some changes over time; however, the primary objective of river basin development, which is the control and effective management and utilization of water resources available within it, still remains unaltered. Humans require water near their settlements and all round the year. However, precipitation follows the laws of nature resulting in a spatio-temporal pattern which many a times is a total mismatch to the human water demand, both in terms of quantity and frequency. Thus, it is very necessary to modify the water cycle to ensure water is available and in acceptable quality, and this is the essence of water resources management (Ayoade 1988). The fundamentals of water resource Downloaded from https://iwaponline.com/h2open/article-pdf/2/1/184/622731/h2oj0020184.pdf" /><meta name="description" content="Abstract. The current review has unveiled the spatial disparity of the surface water resources availability between the upstream and downstream of the Hadejia Existing water resource availability in this river sub-basin based on water balance was matched with potential water demand. The water balance potential of the area has indicated that 75% of the river water between Wudil and Hadejia area will likely get exhausted by 2010 as the water use rate will reach 100% by 2018 The study projected the consequences of increased population and urbanization on the water resource availability 9 Barbier (2003) Determination of the impact of upstream water diversion on downstream activities in Hadejia River Basin (entire basin) Technique: Economic modelling descriptive and regression methods, Data: Secondary data, empirical observations, weather records The study demonstrates the negative consequences of increased irrigation in the upstream area on the wetlands areas downstream. This suggests that the increased expansion of the irrigation project is uneconomical. It is also suggested that the initiated controlled flooding regime would perhaps safeguard the groundwater The study portrays the effectiveness of river basin water management 10 Goes (2002) To determine the consequences of river regulations on aquatic macrophyte advances and the consequent flooding in the downstream of the river catchment (downstream) Downloaded from https://iwaponline.com/h2open/article-pdf/2/1/184/622731/h2oj0020184.pdf" /><meta name="description" content="Abstract. The current review has unveiled the spatial disparity of the surface water resources availability between the upstream and downstream of the Hadejia  (2000) Examining the impact of human activities on the hydrological characteristics of the Hadejia-Nguru wetlands (downstream) Technique: Hydrological survey, analyses of flow data and the flood hydrograph. Data: Hydrologic surveys data, river flow data and flood hydrograph The pattern of land use distribution was found to be influenced by spatial variation in hydrological features. Rice, for example, is favourable cultivation done in the swampy areas popularly known as flood receded. Fishing and animal grazing were also shaped by the hydrological differentiation between the spatial locations There is a need for assessing the changes in the spatial scope of flood inundation area(s) over time using GIS and RS 13 Goes (1999) To estimate shallow groundwater recharge in the lower course of the river (downstream) Technique: Simple descriptive and regression methods. Data: Well records and hydrogeology data The annual inundation of the flood plain area was the principal source of groundwater recharge. The groundwater table started increasing in the first week after the surface inundation The study has not taken cognizance of the increased climate variability on the changing flow behaviour 14 Thomas & Adams (1999) To examine the change that resulted in the past 20 years of Tiga Dam operation (upstream) Technique: Time series analysis and personal interview The impacts of Tiga Dam regulations is the change in flow characteristics exacerbated by drought. However, the agricultural practices are gradually adapting to these changes. The adaptation was facilitated by physiological forces related to these changes and the improvement in agricultural innovations and technologies It is not certain whether the increased production will be sustainable due to increased population and climate change 15 Thompson & Hollis (1995) To determine the sustainability of the Hadejia-Nguru Wetlands contributions on the socio-economic activities of the inhabitants (downstream) Technique: Water balance model. Data: Hydro-climatic data The planned projects intended for the area, if fully implemented, will result in reduction in floods' extent and groundwater storages will drastically reduce due to low recharge. However, an artificial flooding was suggested to facilitate delivery of water to various water users in the upstream and the downstream areas of the basin The study proposes an artificial flood that will take care of all the water demand/uses within the basin H 2 Open Journal management anywhere are to ensure fulfilment of water resources where it is needed. This entails minimizing the consequences of water deficit (drought), water excesses (floods) as well as the effects of water pollution.

Surface water availability, dynamics and uses
Surface water resources are characteristically variable in the basin and a number of factors were found to affect the availability and variability, notably, climate variability, geological differences, land use changes, upstream water uses and the development and clearance of weed and silt blockages in river channels. The major factors are briefly discussed below.
Climate variability (rainfall-runoff scenario along Hadejia River Basin) The adjustment of the overall climate models is mostly subjective to developed nations, where the data collection network is adequately distributed. However, in the developing countries where the impact of climate variability is more devastating due to low resilience and adaptive capacity, the information on climate change is generally poor (Rizwan et al. 2017). There are very little or no available facts in the literature on the impact of climate change on the water resources of Nigeria from the downscaled global climate models, particularly the semi-arid region of the country. Based on the existing climate change scenarios, a decline in rainfall is projected for the West African sub-region ranging from 0.5% to 40% and in the order of 10% to 20% averagely by 2025 (Ahmad & Daura 2019). However, that does not mean a general reduction of the future river water resources of the region; instances are from two different studies from the Volta Basin where an increase in rainfall and river flow was predicted (Andah et al. 2003). It is crucial to note that high spatial runoff variability is also predicted, particularly between the upstream and downstream areas of the Hadejia River Basin (Sobowale et al. 2010). The mean runoff is higher in Wudil station which is located at the upstream of the basin than in the Hadejia station which is at the downstream of the basin. The mean rainfall and river discharge spatial distribution between the upstream and downstream in the basin is also presented (Figure 3(a) and 3(b)), suggesting higher rainfall and runoff in upstream areas and lower mean rainfall and runoff in the downstream areas of the basin. Of all the factors that determine the surface water availability in the region, climatic factors were considered the most important. Rainfall was considered the most important single factor that determines the recharge of both surface and sub-surface water resources (Sobowale et al. 2014). However, the effect of temperature on the river water availability is also considerable; the fact that it determines the rate of evapotranspiration, thus seriously affecting the river water, particularly  impounded river water. A recent empirical study has shown that the impact of rainfall and temperature on river water availability in this basin area is indicated by the disparities and coincidences in the mean rainfall and temperature with the mean of river discharge across the spatial extent of the basin . The spatial interpolation of mean annual rainfall, temperature and river discharge in Figure 4(a)-4(d), modified after Umar et al. (2018), indicates that rainfall and river discharge have a positive relationship; however, river discharge decreases with increasing temperature, thus they were negatively correlated.
Additionally, population growth across the basin and the lack of sufficient information about the real relationship between the current climate change and surface water resource availability further aggravate the problem of surface water shortages in the region.

Geological differences
The volume of surface water decreases from the basement complex to the Chad formation area of the basin. Thus, availability of surface water resource is more abundant in the basement complex than in the Chad formation. The Chad formation area of the basin seems to be the principal manageable store of fresh underground water due to the high rate of infiltration, and for that reason groundwater is often considered a rational freshwater resource in the downstream areas of the basin. Conversely, in the basement complex region of the basin, surface water is relatively available even though rapid population growth in association with urbanization has led to severe pollution of the surface water  resources (Mustapha et al. 2013(Mustapha et al. , 2014. Consequently, there is increased groundwater exploitation evidenced by increased production of water resources via boreholes, essentially for home usage. However, despite the consideration of groundwater as an alternative source of water for different uses in some parts of the basin, the main worries are for the sustainable supply of the resources considering increased climate and land use changes that can affect both the availability and purity of the available water resource.

Surface water uses and changes in upstream water uses
The uses of surface water in the areas differ from agriculture, domestic and commercial uses (Thompson & Polet 2000). Despite the numerous uses surface water resource is put to, increased population and urbanization, particularly upstream of the basin, have necessitated the search for and use of groundwater resources as an alternative source of fresh water for various uses. Consequently, boreholes were drilled by private individuals, governments and companies. Thus, there is a fear of overexploitation of the groundwater resource, with its untold consequences. The most prominent anthropogenic water users in the vicinity of the basin are Kano River Irrigation Project (KRIP), Hadejia Valley Irrigation Project (HVIP) and Kano City Water Supply (KCWS). These three large formal water users all depend on Tiga and Challawa dams for their water supply ( Figure 4). The current surface water abstraction by KCWS is estimated at approximately 30 Â 10 6 m 3 y À1 . Still, the surface water intake capacity is expanding (e.g., at Tamburawa downstream of Tiga Dam), so it is likely that the surface water intake by KCWS will increase to 95 Â 10 6 m 3 y À1 within a couple of years. The projected (2025) surface abstraction is 287 Â 10 6 m 3 y À1 (Neville 2005).
The water demand for all the major water users (KRIP, KCWS and HVIP) upstream exceeds planned water allocations (Oyebande 1995). Population growth and change in cropping pattern are some of the reasons for the excessive demand for more water than planned (Oyebande 2003). An increase in these uses decreases the river flow downstream. However, the impact of KCWS and KRIP on annual flows at Hadejia can be mitigated, to a certain extent, when the river flow relation between Wudil and Hadejia is taken into consideration in the management of releases from the dams. A daily or weekly river flow model, using different release hydrographs from the dams, is required to quantify the minimum, mean and maximum impact on river flow at Hadejia when both large upstream users are working at full capacity.

Appearance and clearance of blockages in river channels
Blockages in channels in the Hadejia River System upstream also affect the flow downstream. In his study, Abdullahi (2009) reported that the basin has been overgrown by an emergence of aquatic weeds belonging to the family Typhacea. The flow would increase if the weed and silt blockages upstream were to be cleared. However, the chance that weed and silt blockages upstream will be cleared is small although there was an initiative by people living along the Kafin Hausa River who regularly make efforts to clear blockages in order to facilitate inflow into the river. The effects of the river flow improvements in Kafin Hausa River are normally short-lived (Thompson & Hollis 1995).

Surface water quality status
The findings of Mustapha et al. (2014) revealed that surface water freshness deteriorates more in the drier period than in the wetter period due to the effect of rainfall recharge and dilution capability. Based on the selected surface water quality parameters (pH, temperature, total suspended solids, NH4 þ -N, and NO3-N), Tukur et al. (2018) investigated the spatial changes of surface and shallow groundwater quality along Hadejia River Basin. The results showed the order of concentration of surface water pollution class ranging from moderate . good . doubtful . excellent using the Surface Water Quality Index (SWQI) model. As seen from the result (Figure 5), there is no excellent water in all the sampled stations, and doubtful water quality class dominates in all the sample stations. This is in agreement with the previous study conducted by Mustapha et al. (2013). However, despite the dominance of doubtful water quality class, there is still the existence of good and moderate water quality class in the area. The higher concentration of doubtful water quality class at Wudil and Hadejia are attributable to the release of industrial effluent upstream of the latter and the application of fertilizer around the former station. Moreover, the deterioration in water quality at the various points of the river suggests increased urban wastewater releases into the river which, according to Goes (2001), is the main cause of increased freshwater scarcity in the area. Thus, a sustainable monitoring culture should be imbibed to arrest the increasing problem of pollution from industrial and other anthropogenic sources.

Recommended management options
From the foregoing, there seem to be some associated threats attached to surface water resources in the basin, such as the water pollution, water deficiency and the ineffectiveness of the prevailing management choices regarding the prevention of water pollution and the adjustment of water scarcity. To improve both the quality and the availability of surface water resources some management approaches are hereby proposed.

Managed aquifer recharge and recovery (MARR)
Managed aquifer recharge (MAR) is reflected as one of the viable means to store the surface water resources when there are water excesses in the wet period (Brunner et al. 2014). It is principally essential in arid and semi-arid areas such as the northeastern part of Nigeria where HRB is located. This can be achieved through artificial aquifer recharge (AAR) (Sharma & Ray 2011). The AAR has demonstrated numerous advantages over the commonly used surface water storages, such as the construction of dams which at present is the only method of surface water storage and management within HRB. This method provides many advantages, such as reducing the risk of surface water losses via evaporation, preventing the risk of flooding during the wetter periods, limiting the vulnerability of surface water contamination by animals and human activities, thus the risk of algae blooms is vehemently reduced. In the process of injecting the water, the subsurface provides soil-aquifer treatment, thus improving the water quality. This stored water can be recovered at and when required through the recovery system.

Surface water reclamation and re-use
Surface water recovery and re-use are considered an option for surface water augmentation and conservation, particularly in drier areas of the world. This can help greatly, regarding the current threats of surface and groundwater exhaustion around most of our urban centres. Reclamation and re-use methods can be used as a substitute to over-dependence on surface and groundwater sources. It can be more practically important in the upstream area where wastewater from industrial areas is frequently produced. In this sense, the wastewater is directed to various urban ponds and other surface water bodies can instead be used to recharge the groundwater after treatment where it can be mixed with ambient groundwater. This will improve the quality of the injected wastewater and in this way reverse the groundwater declination. This improved wastewater will eventually be improved and used again.

Rainfall harvesting and detention pond
This water resources management option has been successfully and popularly practised as supplementary, in some cases, even as a primary water source in semi-arid areas. This technique was necessitated due to the unreliability and insufficiency of rainfall. It was reported to have provided a substantial quantity of fresh water in various regions with wide rainfall variability (Sappa et al. 2015). Instances were drawn from Kuwait, with about 12% of the agricultural water demand satisfied via this means; Muscat in Oman fulfilled 27% of its industrial water requirement through rain harvesting; Abha in Saudi Arabia was able to source 11% of its water demand for industrial needs and irrigation agriculture. Similarly, Ali Ain of United Arab Emirates satisfied 16% of its water demand for agriculture using rain harvesting techniques (Zuhair et al. 1999;Gereish et al. 2015;Sappa et al. 2015). Considering the success stories from around the semi-arid areas of the world, this management practice is worth trying in HRB, especially in the downstream areas where the Chad formation structure and rainfall characteristics prevent the accumulation of surface water in reasonable quantities. The detention pond will be useful to numerous households and small communities, especially in the sedimentary formation of the region.

Riverbank filtration (RBF)
Riverbank filtration (RBF) is a procedure where the bed and bank of a river assist in the treatment of river water induced from the river (Ray 2011;Bradley et al. 2014). The process takes place when wells are suitably positioned adjacent to the river. The process is completed by pumping to induce the river water to flow towards the well(s) via the bed and bank of the river. Serving as the treatment zones, the bank and bed remove most surface water pollutants (Ray 2012;Dalai & Jha 2014) by joint processes including physical, chemical and biological processes (Singh et al. 2010;Sandhu et al. 2011;Abdel-Lah 2013). Thus, considering the high rate of surface water pollution in the Hadejia River Basin, riverbank filtration will considerably assist in alleviating the current and potential water scarcity in the area.

Managing the floodplain areas
Managing floodplain entails all operational and remedial tasks that serve as preventive measures for reducing flood impairments, such as early readiness plans, controlling flood and the task of managing the floodplain areas. Managing floodplain was acknowledged as the best and far-reaching technique for averting impending flood causalities, particularly in areas where there are flood problems (Tanko 2014). Although two main categories of flood control measures exist (structural and nonstructural), in Hadejia River Basin where floods are caused not only by extreme rainfall but also as a result of blockage of river channels, the use of both structural (diversion via reservoir(s), embankments or ditches and channel amendments) and nonstructural measures (flood-proofing, impending flood alerting system and controlling the land use changes) are recommended to regulate the flood runoff.

DISCUSSION
The study has identified areas that experience surface water scarcity and challenges in the Hadejia River Basin, as well as the factors associated with surface water deficiency and challenges, both spatial and temporal. The factors influencing the spatial disparity are many, however, climate variability, land use change, soil and geological differences are the most important ones (Odunuga et al. 2011). Thus, the availability of surface water resources in the Hadejia river basin was found to be spatially variable, with greater availability in the upstream basement complex region (Barbier 2003). The availability decreases northeastward, especially in the Chad formation geological territory. Integrated approaches to surface water management in the basin were suggested. The analysis of river water balance indicates that the groundwater recharge via indirect ways (stream channel seepage) is nearly 1,535 MCM annually and this happens from Wudil to Hadejia stations which are located within the Chad formation geological region (Barbier 2003). However, the direct recharge to groundwater is about 86 mm and 94 mm computed as mean direct recharge observed in the upstream of Wudil and between Wudil and Hadejia station, respectively. In another development, changes in climate and land use were particularly found to affect the surface water chemistry of the basin (Tukur et al. 2018). Evidence is in the spatial differences in dominance of water quality classes with the doubtful water quality class being higher in Wudil and Hadejia ( Figure 5), where the latter was influenced by wastewater from municipalities of Kano and Wudil while the former was influenced by the effect of chemical fertilizers used in irrigation plots around Hadejia area.
On the other hand, surface water availability is higher in the upstream areas (stations between Chiromawa and Wudil). Chiromawa is located at the extreme south of the confluence of Kano and Challawa to form the beginning of the Hadejia Basin, where mean rainfall is higher (Figure 4) .
It is pertinent to note that declining surface water resources are expected to pose additional implications in the downstream region where rainfall is less and temperature is constantly high at most times of the year (Dammo et al. 2015). Consequently, surface water deficit is obvious in the northeastern portion of the basin which is, moreover, underlain by the sedimentary geological structure. This implies high surface water losses via infiltration. Considering the climatic stress and the increasing water demand, routine assessment of surface water availability is seriously recommended, including simulation and projection of future water resources availability in the basin.
On the whole, the review uncovered the inadequacies, particularly regarding the factors affecting surface water resource availability and management and in respect of the methods and techniques used in conducting the few available studies in the area.

CONCLUSION
The review has revealed that the availability of surface water resources differs in quantity and quality between the upstream (basement complex) and downstream (Chad formation) areas of the basin.
Surface water resource is more abundant in the basement complex area than in the Chad formation region. Although many factors contributed to these variations, the basic factors are rainfall variability, geological differences and land use changes. In the upstream areas, higher mean rainfall, lower mean temperature and concrete surfaces due to urban expansion as well as the geology are the reasons for surface water availability. However, in the downstream area, lower mean rainfall, higher mean temperature, gradual land use changes and the high losses to groundwater are the explanations for low surface water resources. Finally, the review has recommended the application of riverbank filtration, aquifer recharge and recovery, and rainwater harvesting to harmonize the flood and drought predicaments as well as improving the surface water quality of the river. Similarly, the use of hydro-climatological models is strongly suggested. To this end, there should be an improvement in data collection and management in the entire basin to assist in generating long-term periodic data to help carry out joined up surface water supervision in the area via modelling approaches.