Evaluation of Morphometric Parameters for Identifying Groundwater Recharge Potential Zone by GIS Application in Kufrah Basin SE Libya

Abstract

A number of studies have been done by using various approaches of remote sensing techniques and GIS applications to discover and identify a great aquifer in SE Libya. One of the main goals of these studies was to find out the source water of this aquifer in the Kufrah basin and how it could be recharged. Modern GIS applications were used in the current study for morphometric analysis of the network streams and delineation of Kufrah basin to identifying groundwater recharge zone. The obtained results show a positive linear relation. The results show that the study area is a flat area with low relief topography, low moisture content and high evaporation rate. The drainage pattern of the Kufrah basin is a dendritic pattern with the 7th order of streams. The network streams over a permeable subsurface material, high infiltration capacity with very coarse texture, and low runoff. The Kufrah river can be described as an “Old age” river and drained inland at Al-Jaghbub area.

1. Introduction

In Libya, the overall usage of water accounts for 97% of groundwater, with less than 3% coming from other sources. A part of the Nubian sandstone aquifer, which is an integral part of the biggest fossil aquifer system in Africa, is located in Libya to the east of the Sahara Desert [1, 2]. This enormous aquifer is believed to have recharged during the Pleistocene and Pliocene epochs, which are known for their extended periods of rainy weather in Libya’s Quaternary history [3, 4]. The presence of freshwater fauna in the Sahabi’s paleochannel, in addition to the width and depth of the Sahabi Canyon, strongly suggests that a massive river drained the southern part of Libya to the Mediterranean Sea via the Sahabi paleochannel and, more recently, internally into the Al-Jaghbub depression’s inland delta [5, 6]. In semiarid and desert countries like Libya, recharging of reservoirs is critical for dealing with population growth, as well as developing water supplies [7].

Although the Nubian sandstone aquifer in Libya is estimated to supply 1020.7 million cubic meters of water per year for all water purposes, it could also be used sustainably [1, 2]. In order to avoid groundwater depletion, the determination of the groundwater recharge zone is essential. There is a direct correlation between the geomorphic parameters, soil profile characteristics, and geological properties of groundwater recharge. Rainfall, drainage density, texture ratio, circularity and elongation ratio, infiltration rate, topography, lithology, and geomorphology all influence where and how groundwater occurs and travels.

However, morphometric analysis of network streams and hydrologic network delineation are thought to be successfully accomplished with the use of remote sensing and GIS applications, which offer a substitute or supplement to field observations and numerical models.

Moreover, remote sensing and GIS techniques have proofed their abilities in penetrating the ground surface and distinguishing the buried features such as channel system (e.g., [8, 9, 10, 11, 12, 13]). Therefore, these tools were significantly used in this study for identifying, discovering, and mapping the water shed of Kufrah basin in Libya. In the current study, GIS application with conventional mathematical equations were utilized for morphometric analysis and delineation of the Kufrah basin in SE of Libya.

Accordingly, in order to approximate the level of development of the drainage network of the Kufrah basin, a hypsometric curve was made to represent the distribution of elevations throughout the river’s catchment region.

2. Location of the study area

The study area is named Kufrah basin, which is located in southeastern part of Libya and covers an area of about 175,000 km². It is bordered by Egypt to the east, Sudan and Chad to the south, and high Tibesti Volcanic Province to the west and from the north by the Al-Jaghbub depression, Figure 1.

Figure 1.

Shows the location map of the study area, SE Libya.

3. Data and methodology

The main data are a Digital Elevation Model (DEM) over the study area that was taken from the Shuttle Radar Topography Mission (SRTM), with a spatial resolution equal to 90 meters. In addition to the geological map of Kufrah basin from Industrial Research Centre (IRC) with 1:250,000 scale [14].

In order to visualize the digital data, ArcMap software was used. The morphometric analysis, hydrology drainage network, and basin delineation have been obtained from DEM by using ArcGIS hydrology tools (10.5), besides a manually mathematical analysis by using equations.

4. The geology of the area

The interested aquifer is located within Kufrah basin, which is an intracratonic sag basin located in SE Libya [15, 16]. The sides of the basin are bordered by highs that made up of the basement, where a succession of Proterozoic and Paleozoic strata crop out, Tibesti Massif in the west, Jebel Uweinat in the east, the Ennedi and Borkou in the south, and Jebel Dalma in the north, Figure 2 [15, 16].

Figure 2.

The geological map of the Kufrah basin.

The Kufrah basin is generally filled with Paleozoic and Mesozoic sedimentary strata. Fluvial, shallow marine sandstones, and shales are the most characterization of the deposition in Cambrian-Ordovician time. The strata of Triassic to Early Cretaceous are made of continental sandstones (Nubian Sandstone) that rest uncomfortably over Paleozoic rocks. The Mesozoic sediments are overlain by fluvial deposits of Messinian to Pliocene and Quaternary eolian deposits (Figure 2) [15, 17, 18, 19].

5. Results and discussion

The results of morphometric analysis of Kufrah basin are listed in Tables 1 and 2, respectively, and they are under major heads of slope, areal, and relief aspects.

Morphometric parameters	Formula	Results	Reference
Basin length (Lb)	GIS Software	733 km	[20]
Basin perimeter (P)	GIS Software	3332 km	[20]
Basin area (A)	GIS Software	174,591 km^2	[20]
Mean Basin width (Wb)	Wb = A / Lb; where An area of watershed; Lb basin length.	238.18	[21]
Drainage density (Dd)	Dd = Lu / A; where Lu total length of streams; An area of watershed	0.18 km^2	[21]
Drainage intensity (Di)	Di = Fs / Dd; where Fs Stream frequency; Dd Drainage density	0.14	[22]
Drainage texture (Dt)	Dt = Nu / P; where Nu total number of streams; P Basin perimeter.	1.28	[23]
Stream frequency (Sf)	Sf = Nu / A; where Nu total number of streams; A area of watershed	0.0243 km^2	[21]
Texture ratio (Rt)	Rt = ΣN1/P, where N1 the total number of streams of 1st order, P perimeter of watershed.	0.004	[20]
Form factor (Rf)	Rf = A/(L)^2; Where A area of watershed; L basin length.	0.32	[21]
Circularity ratio (Rc)	Rc = 4πA/P ^2; π = 3.14, A area of watershed, P perimeter of watershed.	0.197	[24]
Elongation ratio (Re)	Re = 2√(A/π)/L; where π = 3.14, An area of watershed, L length of watershed.	0.0209	[20]
Length of overland flow (Lof)	Lof = 1/2Dd; Dd Drainage density	2.8 mature stage	[23]
Infiltration number (In)	In = Dd * Sf; Sf Stream frequency, Dd Drainage density.	0.0044	[22]
Constant channel maintenance (Ccm)	Ccm = 1 / Dd; where Dd Drainage density	5.5	[20]

Table 1.

List of the morphometric parameters and the formulas used in Kufrah Paleo river analysis.

Relief parameters	Formula	Results	Reference
Maximum elevation in the area (hMax)	_	1887 m	_
Minimum elevation in the area (hMin)	_	239 m	_
Basin relief (H)	H = hMax - hMin	1648 m	[20]
Relief ratio (Rf)	Rf = H/L; where H basin relief; L length of basin.	2.25	[20]
Ruggedness index (RI).	Rn = H* Dd; where H basin relief, Dd drainage density.	0.29 high erosion	[25]
Dissection index (DI)	DI = H/ hMax; where H basin relief, hMax maximum elevation in the area.	0.873	[20]

Table 2.

List of the relief parameters and the formulas used in Kufrah Basin analysis.

5.1 Slope, aspect, and relative relief parameters

One of the most important parameters in morphometric analysis is the slope parameter, which determines how rainwater will run off along the network of the river basin under the effecting of slope [26]. The slope degree map, elevation map, and the relative relief map have shown the study area as a flat area with low relief topography that makes the runoff slow, Figure 3. Consequently, this will give the water more time to seep into the subsurface, greatly recharging the groundwater. However, the highest slope in the study area is only noticed on the far east, where Jebel Uweinat and Jabal Arkenu are located.

Figure 3.

Illustration of the elevation map and the slope map of the Kufrah basin.

The Kufrah water basin starts from an of elevation 1887 m in the south and terminated in the inland delta at Al-Jaghbub depression in the north with 239 m. It has a dendritic drainage pattern, which demonstrates that the rocks and soil type are uniformly homogeneous.

The direction that a sloped landscape faces is referred to as its aspect. The research area’s vegetation distribution, biodiversity, and precipitation patterns can all be significantly impacted by the slope aspect [27, 28]. From the value of the raster data output, the aspect’s compass direction was determined. The aspect map of Kufrah basin is mainly dominated by flat to very gentle aspect slope, Figure 4.

Figure 4.

The aspect map and the hillshade map of the Kufrah basin.

The hillshade map is highlighted the structural effect of Jebel Awaynat and Jabal Arkenu on the eastern flank of the basin, while the rest of the region is not Figure 4.

5.2 Aerial morphometric aspect

The morphometric parameters of drainage density (Dd), drainage texture (T), texture ratio (Rt), infiltration number (In), form factor (Rf), stream frequency (Fs), elongation ratio (Re), circulatory ratio (Rc), and length of overland flow (Lof) are included in the aerial morphometric aspects. Climate conditions, geological structure, and lithology all play a role in determining the drainage basin’s characteristics [29]. Kufrah water basin is believed to be developed over non-resistance rocks, and thereby, the number and order of its streams is high with the 7th order of streams, Figure 5.

Figure 5.

The stream orders and the drainage density of Kufrah basin.

5.2.1 Drainage density (Dd)

Horton [21] initially proposed drainage density (Dd) as a crucial measure of the linear scale of the landform element in the stream-eroded terrain. He defined drainage density as the ratio of the total length of the stream in a given drainage basin and the area of that drainage basin. Furthermore, a variety of characteristics, including the subsurface material, relief, surface runoff, infiltration capacity, flood volumes, and density of vegetation, contribute to both high and low drainage density values. The drainage density of the study basin is 0.18 km² that indicates high permeable subsurface and coarse drainage, Figure 5.

5.2.2 Drainage texture (T)

Drainage texture in the present study shows the value of Kufrah watershed with 1.28, which indicates a texture pattern to be a coarse drainage texture.

5.2.3 Texture ratio (Rt)

The study area has a very low texture ratio of 0.004, which indicates permeable subsurface materials, low relief conditions, and high infiltration capacity with very coarse drainage texture.

5.2.4 Infiltration number (In)

The infiltration number of the basin is 0.0044, indicating high infiltration materials and low surface runoff.

5.2.5 Form factor (Rf)

The basin form of the Kufrah basin is slightly elongated, as indicated by its form factor value of 0.32, which also indicates that the basin has low peak flow.

5.2.6 Stream frequency (Fs)

The high value of stream frequency indicates more surface runoff and vice versa. In the present study, the stream frequency value of the basin is low, which indicates more groundwater potential.

5.2.7 Elongation ratio (Re)

The elongation value of the water basin is 0.0209. The low value indicates that the basin has low relief with moderate to high infiltration capacity and low runoff.

5.2.8 Circularity ratio (Rc)

A circular basin is more efficient in runoff discharge than an elongated basin. Circularity ratio is 0.197, which indicates less elongated basin with low relief and high infiltration capacity.

5.2.9 Length of overland flow (Lof)

The length of the overland flow of the study river is 2.8, and the value is slightly high, indicating that the basin is consists of low relief and slope, and the river is in the mature stage.

5.3 Relief aspects

The relief aspects include Dissection index (Di), Ruggedness Index (RI), and Relief Ratio (Rf). These aspects are calculated and presented in Table 2.

5.3.1 Dissection index

According to Singh [30], the Dissection index (DI) is an important morphometric indicator of nature and magnitude of dissection of terrain, which is expressing the ratio of the maximum relative relief to a maximum absolute relief. The DI value is between zero, which indicates complete absence of dissection or vertical erosion and one that reveals vertical cliff. Generally, the areas with high DI indicate high relative relief where the slope of the land is steep and unstable that results in enhanced erosion. On the contrary, low DI corresponds with low relative relief and with the subdued relief or old stage where the land is flat and more stable [31]. The DI of the study area is 0.873, which indicates the basin is a moderately to highly dissected, Figure 6.

Figure 6.

The dissection index map and the ruggedness index map of Kufrah basin.

5.3.2 Ruggedness Index (RI)

The ruggedness number of the basin is 0.29, which indicates higher soil erosion susceptibility, Figure 6.

5.3.3 Relief ratio (Rf)

The relief ratio (Rh) of maximum relief to horizontal distance along the longest dimension of the basin parallel to the principal drainage line is termed as a relief ratio [20]. The relief ratio of the river basin is 2.25, indicating that this basin is composed of nonresistant rocks, and the basin is under low relief and gentle slope.

5.4 Bifurcation ratio

The bifurcation ratio (Rb) can be defined as a ratio of the number of stream branches of given order to the number of branches of next higher order [32]. By examining the irregularities in the bifurcation ratio, the bifurcation analysis can provide information about the drainage pattern’s structural disturbances, geological and lithological development of the drainage basin, and drainage integration [33]. The bifurcation ratio of the Kufrah watershed is given in Table 3, where the bifurcation ratio is (1.8) that reveals that the area does not structurally controlled with flat terrains.

Rb = Nu/Nu + 1, where Nu = total number of stream segments of order; Nu +1 = number of segments of next higher order	Bifurcation ratios (Rb)
1st/2nd	2.09
2nd/3rd	1.7
3rd/4th	2.8
4th/5th	1.9
5th/6th	0.8
6th/7th	1.8

Table 3.

The bifurcation ratios (Rb) of streams order of Kufrah basin.

5.5 Valley stage

Finally, a hypsometric curve for the Kufrah basin was made in order to surmise the drainage network’s stage of development. The hypsometric curve of a catchment represents the relative area below (or above) a given altitude [34]. The shape of the hypsometric curve provides valuable information on the erosional stage of the basin and also on the tectonic factors controlling it [35].

However, rivers can be classified according to specific characteristics as initial a “Youthful”, “Mature,” and “Old Age”. From Figures 3 and 4, the Kufrah network river can be described as an “Old age” river, showing a more S-shaped feature and displaying a concave upward feature at higher elevation and concave downward at lower elevations, which characterizes an old age of drainage basin, Figure 7.

Figure 7.

A hypsometric curve for Kufrah water basin.

6. Conclusion

The present study has used GIS applications and remote sensing techniques for morphometric analysis and stream delineation of Kufrah basin. These techniques have demonstrated their ability to penetrate the ground surface and identify the morphometry of the buried streams. All the morphometric parameters that have been analyzed indicated same results. The used tools have revealed that Kufrah water basin was running from the south to the north and drained internally into the Al-Jaghbub depression. The Kufrah basin has a very coarse drainage texture, high infiltration capacity, high permeability of subsurface material, and low surface runoff. Furthermore, the basin is composed of nonresistant rocks and thus higher soil erosion susceptibility. The water basin is a moderately to highly dissected with low structural effects. Finally, the drainage network in Kufrah basin is in an “Old age stage.”

Conflict of interest

The authors declare no conflict of interest.