Hydraulic Modelling of Water Distribution System of Aksum Town, Ethiopia

Tesfay Bahre^1* and Sisay Demeku^2
*Correspondence: Tesfay Bahre, Department of Water Supply and Sanitary Engineering, Addis Ababa science of Technology University, Addis Ababa, Ethiopia, Tel: + 251914802115, Email:

Keywords

Water GEMS • Water distribution system • Hydraulic modelling • Maximum pressure • Minimum pressure • Aksum • Tigray • Ethiopia

Introduction

The expansion of urbanization, population increment, and others are the cause which puts increasing pressure on the local water distribution system and water planers to satisfy the growing urban water and sanitation demands in developing countries. According to the World Health Organization WHO (2014) the report, the global drinking water target was met 91% in 2010 while Central Asia, Northern Africa, Oceania, and sub-Saharan Africa did not achieve this landmark.

The water problem is a growing worldwide concern and that has an impact on countries’ economic prospects. Rising water stress, large supply variability, and lack of access to safe and adequate drinking water is a common problem in many parts of the world. Especially, developing countries face greater challenges of adequate water distribution because of their larger population growth rate, poor infrastructure, lower income levels, and less developed policy and institutional capacity.

Intermittent piped water networks were found all over the developing world. And it is estimated that one third of urban water supplies in Africa were operated intermittently. As result of; high population growth rate, scarcity of source water, treatment plant size, reservoirs, and storage tank capacity, power outages to run water pumps, high leakage problems, or some combination of these conditions were the primary causes for intermittent water distribution in the water system.

Aksum town is a serious shortage of water in the distribution system due to the high growth rate of population expanded economic activities, and uncontrolled urban expansion of the town. A water-shortage condition would cause an unbalance in water supplies and demands. This could occur when the water supply decreases and is no longer sufficient for satisfying demand. Water shortage is accelerated by undesirable pressure within distribution systems [1].

Statement of the problem

Currently, Aksum town facing inadequacies and intermittent water distribution systems are the major challenge all over the town due to population growth and town expansion. This research intends to determine the extent to which the hydraulic performance of the Aksum water distribution network is affected by the intermittent supply, operational ways, and management system. To propose appropriate recommendations, we have to study the hydraulic parameters, the variations, and the relations between them and other factors, which control the hydraulic performance of the water supply distribution networks.

Also, it is advisable to evaluate the effects of local conditions and improve them for increasing the efficiencies of the water distribution systems. So, in order to address the overall of Aksum town water supply distribution problem and to give remedial measures, there is a need to evaluate the hydraulic performance of water distribution systems and to define the appropriate design requirements [2].

General objective

The general objective of this research is to model and improve the hydraulic characteristics of the water distribution system using Water GEMS software.

Specific objectives

• To evaluate the existing design, operation, and maintenance facilities of the water distribution system.

• To evaluate the balance of supply and demand in the water supply system.

• To evaluate the existing hydraulic performance of the water distribution system.

Materials and Methods

Description of the study area

Aksum town is located in the Northwestern Highlands Physiographic Unit and administratively belongs to the Central Zone of Tigray Region. Aksum is a historical place where the Ethiopian overall history began before 3000 years. It almost all comprises the center of the Aksumite Kingdom where it was among the four famous kingdoms in the world. Astronomically, Aksum is located at 470520 m E and 1561532 m N at a distance of about 1043 km from the North of Addis Ababa and 245 km away from the capital of Tigray, Mekelle. The town is located at the principal road which connects Adwa to the Shire -Enadasilassie. The town is subdivided into five kebeles and has a woreda status with the urban administration [3] (Figure 1).

Materials and Tools

Based on the research objectives the materials that were used for this study. Among the many commercially available hydraulic software, water GEMSV8i is chosen for modeling pressure in the systems for many reasons. Materials that were used in the study are Arc GIS 10.7 for delineating and locating the study area, Excel Spread sheet: For data preparation, analysis, and interpretation of results, a Pressure gauge to measure the pressure at the nodes and pump outlet, water meter to measure the flow of the pipe, handheld GPS to measure the coordinate’s points.

Data analysis

To analyze the data which is collected from different sources, both qualitative and quantitative methods was used. From the quantitative methods, the descriptive statistical methods like percentage, graphs, and crosstabulation was used in order to come up with the appropriate result. In addition to this, qualitative methods like narration were employed in the study. The computer software application excel was used to analyse the data obtained from the office. The field survey data for the distribution system was evaluated by using the engineering software called Water GEMS V8i.

Population projection

A census record of the population size of Aksum town for different years has been collected from the Central Statistical Agency. CSA method of population forecasting has been adopted for this research. Because of this, a method is mostly practiced to produce comprehensive, timely, reliable, and standardized statistical information using scientific statistical methods like Aksum town [4].

eq. 3.1

Where,

P_n = Design population (after n years)

P_o = Present population (at the start of design period)

r = Annual population growth rate in %

t = Design period in years

Per capita water consumption

The per-capita water consumption for various demand categories varies depending on the size of the town and the level of development. In Aksum town, the growth of the socio-economic activity in both the governmental and private sectors, there was a high water demand in the town. Using the annual water consumption and population in (2020), the average per capita consumption of the town was identified as equation 3.2 below.

eq. 3.2

Domestic water demand

Domestic water demand includes the water requirement for drinking, food preparation, washing, cleaning, and various domestic uses, like Aksum town per capita water requirement, is 60 l/c/day (MoWR, 2006).

DWD= Population* per capital water demand eq. 3.3

Climatic adjustment factor

According to the literature review National Meteorological Agency the climatic condition for Aksum town the mean Temp is 26.50C -300Cwas grouped with the corresponding adjustment factor of 1.1.

Socio-economic adjustment

The adjustment factor usually is based on the ministry of water resource the case of Aksum town was taken with a socioeconomic factor of 1.1

Adjusted Domestic Water Demand (ADWD) = DWD × Climatic factor × Socio economic factor…………eq. 3.4

Factor Uncounted Water loss

Unaccounted for water (UFW) is expressed as a percentage of the total water produced for the system. UFW arises from system leakage, water taken by illegal connections, inaccuracies in metering, overflowing of reservoirs, and legitimate unmetered use such as firefighting, flushing, etc.

eq.3.5

Therefore the total non –domestic water demand can be:

Non-domestic water demand (NDWD) = Institutional + Commercial and industrial + Livestock +Uncounted water loss………….eq. 3.6

Average daily water demand

Average daily water is the sum of domestic and non –domestic water demand. Therefore average daily water demand:

Total average water demand (TWD) = ADW + NDWD…………..eq. 3.7

Maximum daily water demand

Maximum daily demand is the deviation of consumption from average daily water demand. This can be computed by using maximum day factor. From water sector development manual the factor is 1.2.

Maximum day demand = 1.2 × TWD………..eq. 3.8

Peak hour demand

The peak hour demand is obtained by applying a factor of 2-5 to the average daily demand.

Peak hour demand = 1.8 × TWD………eq. 3.9

Demand classification based on land use

Different types of customers and their water use patterns must be considered in this process and customer types are classified as a residential, commercial, industrial, and public institutions. Land use (2020) data of Aksum town was collected from the municipality of town in the form of an AutoCAD file and was prepared using ArcMap GIS tools. The prepared land use of the town has been changed to the shape file with the same coordinate of the network system of the town for the overlying purpose [5] (Figure 2).

Allocating base water demand to each node

To assign base demand to each service node, it is necessary to determine the houses around each supply node. It is a multi-step procedure to allocate water demand to the node, which is as follows:

A. Classification of land use type

The water distribution system is classified into supply areas according to land use, such as residential, commercial, and industrial area, and public service. The map of the town was taken from the municipality of Aksum in AutoCAD file format prepared in ArcMap to change urban land use.

B. Identify the number of the house around each supply node

The urban land uses the town based AutoCAD format was obtained from the municipality of Aksum town. Then the urban land use was prepared in ArcMap. The land use map and the town WDN, which is display in Water GEMS. The number of houses in each census block was physically counted, and assigned to the nearest supply node. An Excel sheet was created for demand allocation.

eq 3.10

C. Population served to each node

To calculate the population served to each node was used the physical counting the number of a house near to the node multiply with the average people per house.

Population served to each node = number of a house near to the node * Average people per house eq 3.11

D. Conversion of the number of houses into the amount of water

The amount of existing water consumption and water loss of the town is 45.7 l/s based on the actual design and based on revised design the base demand of 2020 is 73 l/s. The water Consumption and water loss were taken from Jun 2017-May 2020. Then the fraction of the demand required for those houses around a particular supply node was calculated by the following equation:

eq 3.12

To assigning the industrial, commercial and institution, consumption to each node was calculated using the following formula:

eq 3.13

Conclusion and Recommendations

In this research, the existing WDS is simulated through the construct of a model using Bentley Water GEMS V8i. The actual system was evaluated for the existing design, operation, and maintenance of the network, especially in various abnormal situations. The result evaluated the design, operation, and maintenance facilities were poor due to the wrong model result implementation without modifying, and due to the poor technician. Finally, we can conclude that there is no clear Operation &Maintenance system for the WDS in Aksum town, which ensures the needed for establishing an effective Operation &Maintenance system for Aksum town Most of these problems are created in kebele Meable and Hawelti. After computing the existing system, about 9.1% of junctions are failed to satisfy desirable minimum pressure during steady-state simulation and 13.3% of junctions are failed due to extremely high pressure during the steady-state simulation. Generally, the condition or a situation of the actual water distribution system of the study area is inadequacies. The result of the modified hydraulic parameter is the required allowable design criterion range, especially for Pressure and Velocity [6-9].

The researcher has annoyed to recommend some of the very important issues to improve the hydraulic modeling of the water system.

1. The universal peak factors, which are used in the design of water distribution systems, should be modified and adjusted in the design of new water systems in Aksum town according to the local conditions of operating and managing the distribution networks.

2. Installing pressure reducing valve devices, which decrease pressure, is recommended as a solution to control the occurrences of maximum pressures during low consumption hour for desirable pressure range.

3. Install a Supervisory Control and Data Acquisition system (SCADA). SCADA should be installed at each borehole, valves, and reservoir. Data control signals and system status are transferred to and from the central system employing a bidirectional antenna at the center.

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