Delineation Suitable Rainwater Harvesting Sites in Wadi Al-Mohammadi, Iraq

Water harvesting has become one of the topics of concern to most water specialists, due to its importance in managing water and preserving it from squandering. Wadi Al-Mohammadi is an example of a valley that needs the application of water harvesting and the exploitation of rainwater at all levels, being one of the main valleys in the Iraqi desert where surface water is lacking. The outcomes for water harvesting were derived using the SWAT model. Morphometric, the basin’s shape is far from being circular. Climatologic, the trend line indicates a clear increase in the total rainfall, relative humidity, temperature, and solar radiation, while the trend line indicates a decrease in the wind speed during the observed period. The main contributor to the total flow of Wadi Al-Mohammadi basin was surface runoff of about 99%, the base flow of about 1%, while the groundwater flow did not contribute any amount of that water. The annual average flow discharge was 0.138 m3/s with the average annual water volume being about 4.366 Mm3, while the average annual water volume calculated from runoff was about 4.651 Mm3. Dam 1 is the best-selected site with a suitable index of 97.5 followed by Dam 5, and Dam 2 with a suitable index of 95 and 90, respectively. Hence it falls under the category of highly suitable. The Dam 3 site falls within the modestly suitable category. Finally, the site of Dam 4 could not be established, because they had a suitability index of less than 70.


Introduction
Rainwater harvesting (WH) is the oldest-to-newest technology for collecting water from natural catchment areas to increase the water amount accessible in certain places [1].There has been renewed interest in WH in recent decades, due to the increasing water demand for agriculture and urban development resulting from rising pressure of population and change in climate.WH has been recognized and categorized in a variety of ways by multiple authors through the years.Most definitions tend to be very similar.Water Harvesting is defined as appropriate for the current study area: "Collecting rainwater that flows in the valleys of the basin, by building appropriate dams, and establishing lakes behind the dam to exploit the water in dry periods and use it for domestic purposes, agriculture, livestock, and making it tourist areas, as well as increasing groundwater recharge".1300 (2024) 012021 IOP Publishing doi:10.1088/1755-1315/1300/1/012021 2 There are several methods for enhancing Iraq's management of its water resources, Increases in knowledge, application, and administration (management) of rainwater harvesting systems are also a result of this interest [2,3].The continual examination of water in terms of both qualitative and/or quantitative factors is done in order to ensure the sustainability of this gathered water [4].Water harvesting can happen naturally, such as in depressions, or it can be done artificially with human intervention.Improvements to the gathering of precipitation and directing runoff to the area of application are common in artificial water harvesting.Runoff for water harvesting is encouraged, and it can be produced when it is very low, by smoothing or compacting the soil surface, cleaning rock surfaces, surface sealing, or utilizing impermeable coverings, for example.
Collection area or a catchment, system of runoff conveyance, component of storage, and area of application are the main components of a water harvesting system.The components may be near to one another in certain circumstances, while they may be connected by a transportation system in others [5].Water harvesting is a crucial component (an integral part) of interconnected (integrated) water resource management.Controlled drainage and water storage, working to increase rainwater capture, reduce in-place water loss, and improve agricultural practices.There are various tactics or strategies to distinguish water management.Thus, the water use efficiency is increased.
Several researchers studied the study area and its surroundings in the Western Desert, for example, [6][7][8][9][10][11].They all had different studies on water resources, but like water harvesting, they did not mention it as a water management technique.So the aim of this study is water harvesting through the delineation of the existing watersheds within the study area with morphometric analysis of the drainage within the catchment area of Wadi Al-Mohammadi.In order to reduce the phenomena of desertification, modest lakes along Wadi Al-Mohammadi will promote urban activity and be helpful (useful) for irrigation, agriculture, and the growth of artificial forests.

Site Description 2.1. Study Area
One of the most significant valleys in the Iraqi desert is Wadi Al-Mohammadi, specifically the Western Desert.Its waters flow from west to east towards the Euphrates River.Wadi al-Muhammadi intersects with the Euphrates River at the village of Al-Mohammadi, about 14.5 km south of Hit District.The following coordinates define the basin's perimeter: Latitudes (Lat.)33˚34ʹ18.10ʺ-33˚4ʹ44.40ʺand longitudes (Long.)41˚55ʹ3.80ʺ-42˚56ʹ31.60ʺ(Fig. 1).The basin's overall area is 2286.820km2, and its circumference (perimeter) is estimated to be 487.0km.It rises from 52 to 367 meters above sea level.

Major Parts of the Wadi
Basin of Wadi Al-Mohammadi consists of the confluence of three main streams that form the basin, the following is a description of these parts (Fig. 2): The first main stream, which consists of three valleys: Wadi Al-Mohammadi, Wadi Al-Nakhila, and Wadi Al-Awasel.The second main stream consists of two valleys: Wadi Ashwa, and Wadi Al-Hilali.The third main stream consists of two valleys: Wadi Al-Kasabi, and Wadi Abu Al-Aifin.
It should be noted that most of the valleys in the basin are streams whose depths range from tens of centimeters to several meters, depending on the type of sediments passing through them.After the confluence of the three main streams, the valley runs in a wide stream its width is more than 1 km and the width of this stream increases downstream near its mouth.Several small valleys flow into the main stream of the valley, the most important of which is Wadi Al-Aqabah, which runs southeast of the basin and it is length is 8 km.Flat lands are spread along the stream of the valley called Faidhat, which are lands submerged with water during periods of rain.It is characterized by loose soil with good permeability.In addition, many flat lands in the middle of the basin are vulnerable to flooding when torrents occur as a result of heavy rains.These torrents sometimes cause the Ramadi-Heet Road to be cut off because it was submerged by the valley's torrents.Large quantities of sediments and mud are also deposited around its stream and at its mouth.

Software and Methods Used
Arc GIS 10.8 program has been widely adopted for office work, through several uses such as preparing satellite images of the study area through operations: clipping, mosaic, and composite bands.
It is also used in Re-mapping the geological and tectonic maps of the study area, creating climate maps, and soil maps prepared for the study area in GIS.The SWAT model was used to calculate the curve number (CN) and runoff for a basin of the study area.Determination of potentiale sites for surface water harveseting in two parts: First: Achieving an appropriate map by merging and unifying the maps and weighing the relative significance of the appropriate maps.Second: Severals criteria are takaen into conseideration to determine the consetruction sites for dam.This is done aftar determinning the approperiate areas for the consteruction of dams.Utilizing the ArcGIS10.8program to proccess all data used, in addition to analyzing and interpreting them.
Table 1 The summary parameters of morphometric characteristics for Wadi Al-Mohammadi basin

The Climate
In the hydrological cycle, where evaporation & rainfall are the primary components, the climate is thought to play a significant role in determining how much groundwater & runoff there is in a given area, season, or year, depending on factors such as latitude, proximity to the sea, the absence or presence of mountains, and vegetation.Studying climatic change in a region is crucial since it is intimately linked to quantity and water quality [14].The study area is being influenced by the arid desert environment, and to a lesser extent by the Arabian Gulf & Mediterranean climates [11].Dialy climate data for the rainfall(mm), relateive humidity(%), minimmum/maximmum air tempereture(°C), wind speed(m/s), and solar radeiation(MJ/m 2 /day) are playing an imporetant role in detrmining the

Watershed Delineation
Basin of Wadi Al-Mohamadi was delinaeted utilizing the significant exit point (outlet point), which is locatede naer the basin's confloence with Eupherates River (Fig. 9).

Water Balance of the Basin
Figure 10 summarizes the water balance componenets as annual for the years 1992-2020 on a monthley basis at outlet of Wadi Al-Mohamadi basin, which revaeled that about97% of the annual rainfallwas lost by actual evapotranspiration, while the percoleation value is 0 (zero) & did not affect the amuont of rainfall.The main conteributor to the total flow of Wadi Al-Mohamadi basin was surface runoff about99% of the total straemflow, while the conteribution of the baseflow (laterale flow plus ground water flow) with the percente of1% of the total straemflow.The resultes of the annual avarege show that the ground water flow does not conteribute any amuont of that water.

Surface Runoff Estimation
Surface runoff is the basic material in water harvesting processes and represents the most important part of the hydrological cycle, especially when it comes to water harvesting.The movement and flow of water through basins and the concentration of this flow that ultimately leads to saturated wetlands where runoff is formed are influenced by gravity, topography, and conteributing area [15].Table 2 displays the simulation of Wadi Al-Mohamadi basin's avarege annual rainfall, water flow, and runoff with the basin's total water volume over 1992-2020.From Table 2, the annual avarege flow discharege was0.1380m 3 /s with the avarege annual volume of water being about4.3660Mm 3 , while the avarege annual volume of water calculeated from run-off was about4.6510Mm 3 .There is a differenece in the avarege annual water volume calculatde from surface-runoff and discharege, this is becuase Wadi Al-Mohamadi basin is of a small slope, and not every drop of surface-runoff water makes it to the main stream, or it drains into pits, or it terminates in secondarey valleys, and consequently, surface-runoff exceeds (higher than) discharge.During the heavy rainy season, the discharge reaches about 24.8 million cubic meters, all of which are discharged into the Euphrates River.

Location of Water Harvesting Dams
In arid locations, basins are frequently exposed to erratic and unexpected rainstorms, which may cause floods that could damage populated areas.Flood risks grow as land use and cover shift, especially when vegetation is eliminated.This results in higher surface-runoff rates and lower infilteration rates, which raises the flood proportion hazards in basin [16].Dams can be used to water harvesting during dry seasons (gather water) or to protect the fields from the threat of flooding.The approach of dam site selection has 5 suitability level which were used: Quite suitable (highly), appropriate (suitable), slightly appropriate (modestly), no appropriate (not suitable), and extremely inappropriate (highly unsuitable).For each of the chosen dams with sites on major straems (Fig. 11), an index of appropriateness was utilized.The suitability index (SI) results for the dams above are shown in Table 3, along with the weighted average of each factor's importance for selecting a dam site.The final values for determining the optimal locations of the proposed dams took into account the villages' distance, faults' distance, elavetion, slopes, and roads' distance.These findings demonstrated that the first dam's (Dam1) site is the best choice, with SI of 97.5.After that comes in the second degree the location of the fifth dam (Dam5) and then comes in the third degree the location of the second dam (Dam2) with SI of 95 and 90,respectively.As a result, it qualifies as extremely appropriate (highly suitable).The third dam (Dam3) location fits under the category of moderately appropriate (moderately suitable).Finally, because they had a suitability rating of less than seventy (SI>70), the locations for the fourth dam (Dam4) couldn't be confirmed and established (Fig. 12).Fig. 12. Categories in the SI for potential dam sites

Conclusion
Using the ArcGIS10.8program to processe all the data used, in addition to analyzing and interpreting them with the help of the SWAT model, satisfactory results were obtained for the current study.The basin's shape is far from being circular, which reflects the relatively low drainages, according to morphometric analysis, due to the water waves' extensive distance traveled as they moved from the feeding zones towards the valley's mouth.This increases the likelihood that this water will lose volume through evaporation and infiltration processes.Daily climate data is crucial in establishing the factors that affect how much water is retained using water harvesting technology.The discharge totals around 24.8 million cubic meters during the period of intense rainfall, and it all flows into the Euphrates.Dams that can be built are the ones that have a suitability index greater than 70.

Table 3
Suitable index for choosing dam sites