Geospatial mitigation of the effect of undulating terrain on efficient water distribution network: a case study of Enugu Urban, South-Eastern Nigeria

Access to safe drinking water and sanitation is a universal human right. On July 28, 2010, the United Nations General Assembly recognized the human right to water and sanitation through Resolution 64/292 (Lancet 2020). In 2015 also, the global community set a measurable target in the form of Sustainable Development Goal (SDG) 6, which left countries with the instruction to ensure the availability of a sustainable amount of water and sanitation for their citizens and residents by 2030. Pursuant to this goal, it has become very necessary for cities, regions, and countries to develop and adopt strategic approaches to solving the challenges associated with water poverty within their jurisdictions.

As is true for many residents of urban areas in Nigeria, the inhabitants of Enugu Urban in Enugu State have over the years been confronted with a scarcity of potable water supply. The situation is very peculiar because there are no streams within the city for the extraction of surface water and underground water cannot be obtained in large quantities due to the coal deposit-dominated aquifer in the area. A study by Ezenwaji et al. (2016) compared the quantity of water demanded and supplied in Enugu Urban and noted that the current supply constitutes only 44% of the quantity of water demanded by the residents. In the face of this, successive governments in Enugu State had intermittently struggled to overcome this challenge, but a sustainable solution is not in sight. The efforts of the government in addressing this challenge had given rise to the establishment of some water schemes in the last few decades. These include the 9th Mile crash boreholes program at Udi Local Government Area (LGA), which is about 8.6 km from the city, the Ajali water scheme in Ezeagu LGA, about 21 km from Enugu Urban, the Oji augmentation water scheme at Oji River LGA about 31.7 km away from the city and the recent piped water extension within the city in 2014.

These attempts, though very laudable, had failed to produce the expected results as it has become increasingly difficult for the inhabitants of Enugu City to have access to safe water for domestic consumption. Most residents of Enugu Urban depend largely on water transported by commercial water vendors from privately-owned boreholes at the 9th mile and contaminated shallow wells seen virtually in nearly all buildings and residential estates. A study by Ugwuoti et al. (2018) revealed that in the greater part of the city, children and women are saddled with the responsibility of hulling water from shallow wells to flats in multi-storey buildings for domestic use. This situation has been attributed to poor optimization in the allocation of the available water (Ezenwaji et al. 2014); thus there is a need for the adoption of new techniques that will help in ensuring that water is effectively supplied to the residential, commercial, and industrial areas of the city.

The existing studies have examined the various water distribution network systems: the ring, the grid-iron, the radial, and the dead-end systems and their suitability for different city layout patterns (Adeosun 2014; Anisha et al. 2016; Kiewiet & Telukdarie 2018). Others have focused on the institutional framework for an effective water supply management system (Ezenwaji et al. 2016; Ngene et al. 2021). Yet other researchers have examined the technologies for improving urban water reticulation (Boulos et al. 2014; Srivastava et al. 2021). It is however observed that some of the recommendations such as the Integrated Water Resources Management (IWRM) (Ngene et al. 2021) and the supervised control integrated with the real-time smart water network (Boulos et al. 2014) are currently not feasible in Enugu Urban as their functionality depends largely on well-calibrated facility information and accurate spatial distribution of demands. Ugwuoti et al. (2018) reported that the infrastructure for water distribution in Enugu Urban is haphazardly located without proper planning, and this has made most of them not functional as only three of the 11 water tanks in Enugu Urban were functional.

The available information indicates that the water supply challenge in Enugu Urban has not necessarily been triggered by a dysfunctional institutional framework but by the negligence of terrain configuration and poor distribution network system. Based on this, Ugwuoti et al. (2018) have contended that accurate spatial distribution of water cannot be attained without proper consideration of topography/undulation of the city terrain in sitting water distribution facilities. Moreover, very little is known of the most suitable water distribution system in areas of undulating terrain like Enugu. However, Jaiswal et al. (2021) demonstrated a successful application of geospatial modeling of topographic and remote sensing data to resolve water distribution challenges experienced in Dehradun city of New Delhi India. Moreso, a GIS-based model, was developed to resolve the water pipeline challenges experienced in the irrigational channels of Kostol in the Abu-Simbel City of Southern Egypt (Ayad et al. 2008). It was on this premise that this research sought to examine the application of geospatial technology in mitigating the effect of undulating terrain in efficient water distribution networks in Enugu Urban, Southeast Nigeria. GIS techniques, Digital Elevation Models (DEMs), raster geoprocessing tools, and software such as Arc Map are quick and simultaneous solutions for the assessment, measurement, and analysis of morphometric parameters and construction of thematic maps needed for spatial planning, water resources management, and similar purposes (Cadraku 2022). Remote sensing, which is also a geospatial technology tool, has been proven to be suitable for superior monitoring and environmental change detection (Dibs et al. 2023)

To achieve this, the following two specific objectives were set: (1) survey the existing water distribution facilities in Enugu Urban, southeast Nigeria and (2) develop an efficient water distribution network map for Enugu Urban using geospatial technology. Therefore, this research will inform stakeholders on how geospatial technology can be applied for efficient water distribution systems in urban areas and cities with undulating topography.

Topographically, Enugu is surrounded by the Udi hills and stands at an elevation between 125 and 380 m above mean sea level with intervening hills and valleys. It has a mean daily temperature of 26.7 °C (80.1°F) and experiences two main weather conditions: the rainy season and the dry season and a short harmattan season lasting a few weeks in the months of December and January. The average rainfall in Enugu Urban is around 2,000 mm (79 in.), which arrives gradually and finally becomes very heavy during the rainy season.

Evidence in the literature reveals that there have also been calls for institutional reform, water demand management technique, and supply measures with professional community based management options (Ezenwaji et al. 2016). This has given rise to the advocacy for a paradigm shift in water management from the traditional sectoral approach to IWRM (Ngene et al. 2021). It is also pertinent to note that IWRM is based on a legal and institutional framework that is hinged on water governance and good policy formulation, and this has been widely employed in optimization of water supply and demand equilibrium in a functional water distribution system. These are products of a proactive water management and distribution network system that has been based on integrating supervised control and acquisition systems with the network simulation models driven by real-time smart water network decision support adopted in the city of Las Vegas, USA (Boulos et al. 2014).

It has also been established in the existing study at Maryland, USA by Srivastava et al. (2021) that the utilization of datasets from earth observation satellites in combination with GIS, artificial intelligence, and hybrid technique can be very useful in improving urban water distribution systems. Based on this, four types of urban water distribution system network layouts have been identified and adopted in different countries. These distribution systems are: the ring, the grid-iron, the radial, and the dead-end systems (Adeosun 2014). The ring water distribution network layout system has its main distribution pipes forming a ring around the distribution area, while its branches connect crosswise to the main pipes and to each other. This system is suited for cities with well-planned streets and roads and has been adopted in China as reported by Kiewiet & Telukdarie (2018). The grid-iron water distribution layout system allows water supply to streets from many directions from the centrally located main. It is most suitable in cities laid out in rectangular plain (Municipal Water Supply systems 101: Types and Components 2020). In the case of repair, only a small fraction of the water line is affected. Kiewiet & Telukdarie (2018) reported that this system has been applied in cities in Pakistan and Russia.

There is also the radial distribution network layout system, which is a zoned system whereby the entire distribution area is divided into a number of distribution districts, with each district having a centrally located reservoir. Each reservoir has distribution pipes that run radially toward the ends of the districts and provide seamless services without pressure head loss. It is also the most economical system when a combination of pumping and gravity flow is adopted as found in Britain (Kiewiet & Telukdarie 2018). The dead-end system, also known as the Tree distribution system, has one main pipe that usually runs through the center of the distribution area. The sub-mains divide into many branches from where provision is made for service connections, which make it possible for every street to be supplied with water directly from the main pipe. This is usually adopted in cities where irregular development had occurred or for future extension to where such is envisaged as seen in Chirala Municipal in Prakasam District of Andhra Pradesh, India (Anisha et al. 2016), and in Egypt, Greece, Italy, North America, and the United Kingdom (Kiewiet & Telukdarie 2018).

From the existing studies reviewed here, it is evident that the adoption of each of the four types of urban water distribution system networks is usually a function of the road networks and terrain of the area. It can also be inferred from these studies that based on the peculiarities of locations, two or more water distribution system networks can be combined. In this wisdom, in areas of undulating terrain, the radial system of water distribution layout which allows the division of the area into districts and establishment of a reservoir at the most elevated points of each district can be more effective than any other system. Similarly, it is also possible that the dead-end system of water distribution network can be combined with the radial system to create room for future piped water connectivity and spatial growth of urban areas and cities. In this line of thinking, understanding the spatial or road/street layout and topographic variables is essential for the design and development of effective and efficient water distribution networks/systems for any urban settlement.

The data contain about 301 tiles and each tile contains several points. This made the process of extraction and interpolation for the gaps that can be seen on the figure very cumbersome. Heights along the main/transmission lines were extracted at 50 m interval. These values were brought into an Excel spreadsheet for proper organization. The transmission lines were in most cases established along major roads within the urban area. As a result, the names of the roads through which the lines passed were used to identify each transmission line. It is also important to note that most of the lines traversed several streets, so in such cases, a collection of the names of the streets through which the line passes were used to identify such transmission line(s). The extracted coordinates are based on the Universal Transverse Mercator (UTM) Zone 32 reference origin and World Geodetic System (WGS) 84 datum. A sample of the extracted coordinate is shown in Table 1. The profiles of the transmission lines were plotted with the height component of these coordinates to determine the possibility of water flow from the tanks at New Market area to the reservoirs in different parts of the urban area. The profile was plotted with Auto CAD Civil 3D software.

Between the year 1957, the time the existing map of Enugu Urban water distribution network was designed, and 2021 when this research was carried out, there have been several new installations and improvements on the water facilities in the urban area. Hence, to understand the current challenges facing the water supply system in the area, a design of the map of the totality of the facilities was produced using information acquired from the satellite image and the coordinates of the facilities acquired during ground truthing with GPS. The coordinates of the locations and capacities of the existing facilities (reservoirs, tanks etc.) were assembled as shown in Table 2. These coordinates of existing facilities enabled the indication of the location of tanks and reservoirs in the map produced.

With all the facilities in place, it became very clear from the map of the existing facilities that the distribution network did not agree with any of the four: grid-iron, ring, radial, and dead-end standard water distribution network layouts. However, considering the undulated topography of the Enugu Urban area, the most suitable water distribution layout is the radial system. The natural relief of the Enugu Urban area is such that the radial system is the most appropriate water distribution network layout for the city. Its application has not only allowed proper management of water resources within the zones but has also reduced the economic requirement of water distribution as water flows through the pipes from the reservoir to the houses by natural gravity. This has eliminated the use of pumps and its attendant routing maintenance in the system.

Using the map of the existing facilities and in consideration of the topographic view of the urban area, the city was divided into 12 zones with each of the three LGAs having four zones. In each of these zones, the most elevated central point was considered for the siting of the reservoir from where water is reticulated to all parts of the zone by gravity. The map showing these zones was produced in ArcGIS software environment which allowed for the integration of datasets from the satellite imagery, the ground truthing and the map of the existing facilities. The efficacy of the designed water distribution network was tested using EPANET software. This software consists of a computer program that simulates hydraulic behavior within a pressure pipe network (Saltana & Sultana 2019). The confirmation of the efficacy of the network was made possible by adopting the following Hezen Williams specifications in the software: PVC pipes of 130 mm. Base demand of −333.33 at the first node linking the reservoir. The road junctions were automatically the nodes, while the heights of points and the distances extracted from the satellite imagery were inputted adequately.

The coordinates of the transmission lines were extracted at 50 m interval. This interval was chosen irrespective of the expanse of the work done to capture the rugged undulation of the topography of the area.

All the pipe-borne water distributed within the urban area are from the 4 million gallons, 1 million, and 20,000 m³ tanks at New Market area of the city. All the water sourced from Ajali, Oji, and 9th mile are assembled into these tanks for onward transmission to the end users. The map of the locations of the reservoirs was plotted with the coordinates depicted in Table 3; these locations are points of highest altitude in each of the zones.

In consideration of the topography, settlement pattern and the operation of radial system of water distribution network, a map showing the districts/zones and the respective locations of new reservoir were produced as shown in Figure 8. Apart from the reservoirs, the map also indicates the location of the booster pump where there is an upshot of elevation that resists a free flow of water from the New Market to the Coal Camp reservoir.

Zones such as Amechi, Akwuke, Amorji, and Ibagwa are villages that have emerged to be part of the urban area. Increase in urban migration has made the city expand into these settlements, and thus they had integrated them into these three LGAs that make up Enugu Urban. To accommodate the existing settlement pattern in these villages and also maintain a standardized layout of water distribution, a combination of radial system and dead-end systems of water distribution network layout was employed. In both situations, the reservoirs were stationed at points of highest elevation, while tree-like dead-end design was implemented to follow the settlement pattern of the villages with provisions for future expansion.

With these results, water can be conveyed from the source tanks at New Market effortlessly to all the reservoirs in the zones. The base map also makes it very easy for the authorities of the agency in charge of water distribution in the Enugu Urban area, to assign different reservoirs to different source tanks for their respective supply of water. The water in the reservoirs at the most elevated point of the zones is reticulated by gravity to the inhabitants of the zones. This is very effective and reduces cost for the government and the end users. This is because, when water flows from a higher elevated point to a lower point by gravity, it requires no pumping cost. This design also gives room for proper management of water in the urban area. Each zone could be assigned to be managed by a unit of Enugu Water Corporation, to ensure quick responses to maintenance of facilities and demand of the end users.

It is pertinent to note finally that geospatial technology can be harnessed to resolve all anomalies arising from the undulation of the earth’s surface. This is because it is equipped with remote sensing and GIS that enables the acquisition of satellite based details of the environment and processing for the extraction of attribute data, respectively. This novel approach and a combination of radial and dead-end standard systems of water distribution have not been used in the previous studies of this kind. Most times the city undulation is not considered in the design of water distribution, and even when it is, it is taken along each distribution lines not holistically in the planning of water facilities for an entire city.

This research aimed at demonstrating how geospatial technology can be used to develop an efficient water distribution network for urban areas with undulating terrain using Enugu, southeast Nigeria as a case study. The study found that water distribution in Enugu, Nigeria has been constrained by the undulating terrain and poor distribution network system leading to perennial water supply challenge in this city. To address this challenge, a proper evaluation of the existing distribution network was done by means of updating the existing map with the location of the existing facilities obtained through ground truth and GIS. Remote sensing technology was used in extracting heights of points on the terrain from LiDAR satellite image and the design of a new map suitable for adequate water distribution network was done in ArcGIS software environment. Resulting from these was the division of the entire urban area into 12 zones following radial standard water distribution layout system and a combination of the dead-end standard water distribution network system to cater for future city expansion. The radial layout system permits zoning of distribution areas and location of the reservoirs at the center of the area. The efficiency of this water distribution system was tested in EPANET 2.0 software, and the results revealed that it can be adopted in urban areas or cities where undulating topography possess a significant challenge to effective distribution of water. Moreover, this system is very economical and efficient as water distribution is mainly by gravity and each district or zone can be put under an administrator for adequate management. However, the success of the distribution system is incumbent upon availability of adequate volume of water from the intake sources. We recommend that the Government Reserved Area (GRA) and Ogui New Layout zones should be served water from the 20,000 m³ tank, while the other 10 zones are served by a combination of 4 million and 1 millon gallon tanks situated at New Market area.

All the authors (A.I.U., O.C.O., E.O.I., and V.N.U.) agreed to contribute their knowledge and skill to the production of this paper. The authors also agreed to publish the manuscript with A.I.U., the leader of the team, to be the first author and the corresponding author.

All the contributors to this study gave consent through a form issued to them by the lead author. Even all those who rendered assistance during the period of data acquisition, data processing, etc. gave their consent. The same thing applies to participants who assisted in typesetting and transportation of the lead author to the locations of the available sources of information used in this study. Some of the persons were paid off at the end of their services while others rendered voluntary services to the success of the study.

All the authors signed and gave their consent for the publication of all the details pertaining to this study. These include maps, tables, data, figures, etc. to be published in Water Resources Management. They all confirmed that they have seen and have been given the opportunity to read both the materials and the article as attached to be published. They have all discussed with the lead author and submitted their email addresses for further investigation by the editor of Water Resources Management (O.C.O.: Ojinnaka [email protected], E.O.I.: [email protected], V.N.U.: [email protected]).

All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by A.I.U., O.C.O., E.O.I., and V.N.U. The first draft of the manuscript was written by A.I.U. and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. The authors also have no relevant financial or non-financial interests to disclose.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.