Fadama areas in the Sokoto/ Rima area with potential for shallow groundwater development were identified by WEC (1988). These they categorized into major, intermediate and minor Fadama with an estimate of their areas. A total area of 280,000 hectares was identified as having significant potential. The major Fadamas of the Niger and Sokoto/Rima River floodplain constitute over 60 percent of the potential development area. Moreover these Fadamas are rated as having the best potential and the highest yield from individual tube wells. Their aquifers are made up of alluvial sands which attain a thickness of over 25 metres on the Niger River floodplain and up to 15 metres on the Sokoto/Rima floodplain.

Intermediate fadamas constitute almost 20 percent of the potential area. Most of these fadamas are classified as having good potential but some unsuccessful tube wells should be expected. The aquifers are primarily alluvial sands and gravels 8 to 15 metres thick. An exception is the Zamfara River floodplain where alluvial sands over 20 metres thick have been intersected in a test hole at Gummi.

Minor fadamas make up the balance of the total. Most of these are either small isolated alluvial deposits or long narrow floodplains having moderate to low potential. The aquifers in the sedimentary terrain are mainly fine to medium grained alluvial sands and underlying sedimentary sandstones. On the minor fadamas in the crystalline terrain the aquifers are alluvial sands and fine gravels which have limited areal extent and change rapidly in their ability to transmit water. Tube well yields from these water bearing zones vary considerably. Wells completed in the coarse sand and fine gravel zones have yields over 300 l/m. whereas within a short distance a tube well in a finer portion of the deposit will be reduced to 60 l/m.

The Rima fadama spans from Sabon-Birnin in the east through Sokoto, Argungu, Birnin Kebbi, up to Bunza in Kebbi state Swindell (1986). The general trend of annual rainfall distribution shows greater rainfall in the south (1008 mm) with an onset of the rain around April while further North around Sokoto town the rainfall averaged 740 mm which drop to 658 mm at the Northern edge of close settled zone where the rain did not usually start until June and in some years finish by mid-September.

According to WEC (1988), the Sokoto/Rima zone has 2 million hectares of arable land out of which 1 million hectares is cultivated under rainfall condition, again, there are 425,000 hectares of irrigable land out of which 225,000 hectares are of high potential, however out of this total, only 60,000 hectares is now under various types of irrigation where garlic, onions, tomatoes rice and occasionally wheat dominate dry season crops. With the alluvial aquifer yielding on average 1.0 to 5.0 l/s, AQUASTAT survey (2005).

The alluvial sands and fine gravel aquifers have transmissibilities in the range 400 to 1200 m²/day and storage coefficients in range 10⁻² to 10⁻⁴ based on three pumping tests, indicating semi-confined conditions. Complex aquifer conditions are reflected in boundary conditions. Water levels were not monitored but are expected to fluctuate an average of less than 1.5 m over the dry season/rainy season cycle. The lowest water levels occur in May and the highest water levels in October/November. Recharge to the aquifer occurs through infiltration of surface waters during the rainy season and is augmented by upward flow from the underlying sedimentary bedrock formations Figure 2.

The aquifers in these areas are alluvial sands and gravels which forms small discontinuous deposits. They have little prospect for obtaining significant amounts of water from the underlying crystalline rocks. The transmissibility of the alluvial aquifers ranges from 150 to 1500 m²/day based on the results of 5 pumping tests as conducted by WEC (1988). According to the same source, the storage coefficient varies from 10⁻² to 10⁻³ indicating mainly unconfined conditions with some semi-confined aquifers. The variability of the transmissibility is Indicative of the variability of the sand and gravel deposits. At most sites fine to medium sands constitute the aquifer material, but in some cases, fine gravel aquifers provide quite good yields from individual tube wells. Recharge to the aquifers is entirely from surface water infiltration.

Afaka (Rivers Chidawaki/Chikaji)

The Fadama of Chikagi/Chidawaki has an aerial extent of 23.6 km² (Figure 3) A group of four boreholes designated as GWR −1/1, GWR −1/2, GWR −1/3 and GWR −1/4 were drilled, pumped-tested and monitored for the construction of the borehole hydrograph. The drilling was preceded by surface geophysical investigation using resistivity methods, Eduvie et al. (1999). The results of the drilling show that the only significant aquifer is the alluvium of the Fadama and

the underlying weathered zone of the basement complex (Figure 3). The aquifer consists of alluvial sand and gravel, containing significant quantities of vegetation and wood remains. It is underlain by clayey silt of the weathered zone grading down into sand-size particles and fragments of decomposed basement rocks, GWRD (1986). The aquifer is phreatic with the water table lying about 2.0 m below ground surface. The thickness varies from 14.0 m at borehole GWR −1/1 to 26.0 m at borehole GWR −1/3. A cross-section of the area is shown in Figure 5 GWRD (1986). The results of the pumping test are presented in Table 1.

River Gurara Alluvium

The investigation of the potentials of the alluvium on the flood plain of the River Gurara (Figure 4) was principally aimed at using the raw water source for the Kaduna Multi State Water Supply Project to supply Kwoi town and environs. To prove the existence of the anticipated coarse alluvium from geophysical investigations, a test drilling and pump test of three boreholes were carried out. The boreholes were drilled by augering and vibrobailing, with one of the boreholes terminating at 8.0 m depth whilst the other two terminated at 7.0 m depth, Eduvie et al. (1999) coarse sands were encountered in each hole beneath the top surface silt-fine sands. The details of the pump test results are presented in Table 2.

Fadama Potential

Generally, potentials for groundwater development along several floodplains is good to excellent including sections of the Kaduna, Galma, Karami, Kachia, Tubo, Kuri, and Shawu Rivers. Shown in Figure 3, is the location of Alluvium (Fadama) boreholes at Chidawaki/Chikaji and Figure 4 shows the location of Gurara Fadama. The Pumping test data of sixteen (16) tube wells in flood plain and other parts of Kaduna is listed in Table 3 showing pumping yield range of

(Note: PZ is piezometer and PM is pumping boreholes) GWRD (1986).

Source: WEC (1988) and Eduvie & Ndahi (2012).

0.75 L/Sec to 2 L/sec. Groundwater is present in aquifers composed of alluvial deposits above bedrocks and fracture system. Shown in Figure 5 is the hydrogeological cross-section at Chidawaki/Chikaji Fadama Eduvie et al. (1999), Eduvie & Ndahi (2012).

The Komadugu-Yobe River Basin (Figure 1) is situated in the Sudan-Sahel zone of northeast Nigeria (~85,000 km²; and southeast Niger (~63,000 km², Oyebande, 2001). Most of the flow (~80%) in the Hadejia River system, which is a tributary of the Yobe River, is controlled upstream by the Tiga Dam (completed in 1974) and Challawa Dam (completed in 1992, Figure 1). All three tributaries of the Yobe River are effluent until they reach the geological boundary between the largely impermeable rocks of the Basement Complex and the permeable sands, gravels and clays of the fluviatile and lacustrine Chad Formation where their regime changes to influent system Hamidu et al. (2017).

The mean annual rainfall ranges from over 1000 mm in the upstream Basement Complex area around Kano, to approximately 400 mm in the middle part of the basin and less than 300 mm near Lake Chad. However, climatic variability has resulted in these mean annual rainfall values being unrepresentative for different periods. Hess et al. (1995), calculated an average decline in annual rainfall of 8 mm∙yr⁻¹ between 1961-1990 for the north-eastern arid zone of Nigeria (i.e. the middle and lower part of the basin). Since the mid-1990s the decreasing trend in annual rainfall seems to have been reversed with a recent trend of increase in average annual precipitation, Oyebande (2001).

Madachi Fadama (Hadejia-Nguru wetlands)

Although most of the irrigation practiced in this basin is the use of surface water from rivers and Dams, there are areas that use the shallow groundwater of the alluvial Fadama/floodplains for, this purpose. The following sections reviewed three areas within the basin which utilizes and depends on the Fadama shallow groundwater resources for both domestic and irrigation needs.

This surface water body is form by the flooded waters of the Hadejia and Jama’are rivers which are ephemeral with 80% of the run off occurring in the months of August/September and this is responsible for the recharge of the shallow alluvial aquifer recharge, Hollis & Thompson (1993). A total of 230,000 ha of cultivated floodplain have being estimated for the wetlands, Mukhtar (2018).

According to a survey carried out, Barbier et al. (1993), a total of 963 tube wells has been drilled in the 66 km² Madachi Fadama but only 309 are operational and are used for the abstraction of groundwater. Maximum depths of 9 m have been recorded for the tube wells, while static water level is at 6 or 7 m and aquifer recharge is dependent on the flooding of the wetlands during the raining season.

Katarko Village River Anumma (Gongola River tributary)

This Fadama is classified as seasonal stream side Fadama, Acharya & Barbier (2000), which is characterized with low gradient and poorly defined channels which leads to the deposition of clay, organic materials and debris, which resulted over time to the development of interbedded layers of silt, clay, sand and silty loam overlying the sandy materials. These irregularities give rise to pockets of aquifers through-out the floodplain which are either overlain by aquitard or occur as parched aquifers above thin impervious materials, Tarhule & Woo, (1997). Hydraulic conductivity for the shallow aquifer ranges between 100 to 101 m∙d⁻¹, aquifers with high conductivity values have thick sand layer greater than 0.9 m, when it is extensive it can yield water up to 5000 ld⁻¹∙m⁻² without any appreciable drawdown, while shallow hand dug wells in the Fadama have a depth that rarely exceed 4 m.

Bauchi Fadama shallow groundwater on Jama’are and Gongola rivers

The Gongola and Jama’are Rivers system are characterized by shallow Fadama areas, with substantial part of the Hadejia-Jama’are river basin lying in Bauchi state. Accordingly Turner, evaluated the shallow groundwater potentials of the Fadama areas on the Jama’are and Gongola Rivers within Bauchi State, their study revealed Tube wells on the Jama’are to have depths that range from 7.05 to 12.23 m, with a yield that is from 0.45 to 6.05 l/s and recorded static water levels of wells has a range of 2.32 to 5.62 m. The River Gongola Fadama area has well depths that range from 2.68 to 6.84 m with yields range of 1.66 to 9.43 l/s while static water levels in tube wells stood between 1.03 and 3.3 m. their findings revealed more groundwater potentials for the Gongola Fadama area compared to Jama’are which can be traced to the amount of rainfall and subsequently flooded waters received by both rivers.

Yola shallow Fadama groundwater of the Upper Benue River

The Upper Benue basin with a catchment area of about 750 km² has the Benue River as the largest perennial river that is fed by two major tributaries of River Faro and Mayo Kebbi with a discharge of about 3500 m³/s 14. Abubakar Sadiq et al. (2014). Before the construction of the Lagdo Dam the flow of the Benue at Yola gauging station in November to June was 10 to 20 m³/s, Toro (1997)

River Katsina Ala Shallow floodplain aquifer

River Katsina Ala is a major tributary of the Benue River; it flows 200 miles, 320 km in the Cameroon and has an area of about 2402 km². Pumping test analysis conducted on 5 tube wells on the floodplains of the Katsina Ala River by Obiefuna et al. (1999), gives a yield that ranges from 1719.36 to 3075.94 m³/day with tube wells depsths ranging from 6.8 to 9.2 m, static water levels in the shallow wells are from 3.7 to 5.25 m. Computed transmissibility values are from 205.92 to 1157.76 m²/day with a maximum drawdown value of 1.83 m recorded for the alluvial aquifer on this floodplain.