Assessment of Haditha Dam Surface Area and Catchment Volume and Its Capacity to Mitigate Flood Risks for Sustainable Development

Within a nation or region's hydrological system, dams play a significant role. By lowering the danger of flooding and increasing the amount of energy that can be generated, they aid in the irrigation of vast tracts of land with surface water and aid in the urbanization of regions downstream [1]. The function of dams in Iraq is seen in the way they store water, control river flow, and supply water for a variety of uses, including irrigation [2].

Although dams and reservoirs are naturally occurring, numerous man-made structures are built to regulate them. Landslides, volcanic eruptions, and rising ground pressure are examples of geological phenomena that can construct mountains and create rock dams that stop lakes from forming [3]. Iraq's hydrological system is mostly dependent on the Euphrates and Tigris rivers, however there are other sources of water that are used for diverse purposes. Along these rivers, several dams have been constructed to regulate reservoir capacity and water outflow [4]. One of the most significant dams constructed in Iraq on the Euphrates River, Haditha Dam is used for flood risk reduction, irrigation, and water storage [5].

River flooding may have negative effects on the economy, society, and environment. The inadequate knowledge of regional differences in flooding has, however, resulted in a number of poorly understood flood patterns and hazy projections of future floods. Studying the lack of reaction to floods benefits greatly from an understanding of the underlying mechanisms. It is crucial to concentrate on evaluating floods over big regions, especially repeated occurrences like yearly peaks. Rarely researched [6] are several catastrophic flood alterations that only sometimes occur at a tiny number of locations having records of continuous monitoring. In summary, flooding happens when water builds up and floods wide regions, much like flowing water.

Heavy rainfall or a rise in the amount of water that is greater than the capacity of typical watercourses, such as lakes, rivers, or reservoirs, might cause it to be channeled to storage zones. Most flooding is dangerous and results in home devastation [7].

All storage alternatives are estimated to be affected by the effects of environment change. Longer droughts, less precipitation, and efforts to keep soil water levels constant are a few examples of this. These elements help to raise the soil's moisture content, which has an impact on crops [8]. Groundwater recharge brought on by increasing sea levels may be lessened if the leakage rate declines. As a result, there is a major danger that coastal aquifers will be exposed to a significant amount of saltwater intrusion [9].

Various external elements connected to different forms of storage are also impacted by climate change. For instance, areas where there is extensive water storage serve as breeding grounds for insects like mosquitoes, which may spread a variety of harmful waterborne infections [10-13].

In addition to serving several other purposes, the primary objective of many dams constructed for the purpose of generating power or storing water is to reduce the danger of flooding. One of the major long-term effects of groundwater recharge and dams is the provision of water for several municipal and local uses. In order to provide water, dams hold water when it is at its lowest point.

This allows for the irrigation of several farmed regions, particularly during dry seasons. Dams increase water, particularly on the lower side, while decreasing the usage of groundwater [14-19]. The features of surface flow, as well as how it interacts with surface water and groundwater, are mostly influenced by the reservoir's management. This is where the connection between drainage and recharge changes [20-24].

From the above, it can be inferred that the water surface and the watershed's size influence numerous modifications that transpire at the water sheet's level, particularly with regard to the quantity of water that is utilized by people. It is anticipated that groundwater levels between the source and the downstream will be directly impacted by contemporary dams. Furthermore, groundwater rises on reservoir surfaces in several natural scenarios.

The formula of water balance is mainly based on the inflow towards the reservoir area. The volume of water in a catchment region is also significantly influenced by the intensity of the rainfall and possible evaporation. The initial storage volume before any changes is equal to 827×10⁷m³. Figure 3 demonstrates the variation of monthly outflow in Haditha Dam. According to this figure, the highest amount of outflow was observed in January. Once the water balance equation with the imposed variables were calculated, the outputs were shown in Table 5.

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Figure 3. Variation of monthly outflow in Haditha Dam

Table 5. The determined catchment with respect to water elevation, after applying the water balance equation with the imposed variables

3.1 Model evaluation

The water quantity balance equation can serve as the foundation for the applied model that can be utilized to manage Haditha Dam's water capacity. If we assume that there are variables x1, x2, x3, and so on, we may write the equation like this:

$x 1-x 2+(x 3-x 4) A=x 5$           (2)

where,

x₁ = rate of inflow (m³/sec),

x₂ = rate of outflow (m³/sec),

x₃ and x₄: rainfall intensity and the evaporation (in mm),

x₅ = the current storage rate,

A = area of reservoir.

By assigning other parameters as M and EL

where,

M= month number 1 for January, 2 for February and so on

EL = Elevation (m. s. l.)

The equation that represented the occupation of water quantity in storage zone between two elevations is:

$\mathrm{A} \times\left(\mathrm{EL}_2-\mathrm{EL}_1\right)=\mathrm{x}_1 * \mathrm{t}$            (3)

where,

t= time to occupy the storage zone

From two equations:

$\frac{\mathrm{A} *(\mathrm{EL} 2-\mathrm{EL} 1)}{t}=x 1-x 2+(x 3-x 4) \mathrm{A}$           (4)

t = f(M),

A = f(EL).

3.2 Model results

The elevation of the water surface can be calculated by subtracting the depth to water from the ground surface elevation. Then, comparisons of water elevations can be made between monitoring well locations and the direction and gradient of water flow can be determined.

Dam water is referred to as retained or stored water. One of two units of measurement is available: "Cusecs" or "Tmcft." Cusec is the colloquial shorthand for "cubic feet per second." The conversion to 28,317 liters per second is possible. Outflow is the water volume that leaves a reservoir per second by the spillway of Hadith dam; and withdrawal is the water volume that leaves a reservoir per second only when it is specifically withdrawn.

Given the knowledge of the relationships S=S(h) and Q=Q(h), one can calculate the height of the tank and, consequently, the discharge at the end of the time step using (S2+Q2 ∆t/2). To cover the whole flow hydrograph, repeat this process.

Table 6 tabulates the predicted monthly outflow of the dam with respect to current elevation for the first four month of the studied year.

In summary, the findings demonstrated that the carefully regulated lowered flows of the dam and clear water discharge created significant modifications to the channel and its flow regime, and that the water surface height was decreased as a result of the reduced water releases and low flow under the Haditha Dam's quantity design. The intermediate lands in the research region emerged as a result of this.

The study calculated the amount of time needed for water to reach a specific height using the water balance equation and the data that was gathered. The water level rose from 147 meters to 154 meters in the least amount of time, 10.7 hours, in January. The longest brief time occurred in January and lasted 10.7 hours. Each month's data was displayed in graphs by the research.

A significant volume of flow was sent downstream in January to sustain the dam without any concerns, indicating a very urgent condition. HEC RAS was used to model the flood. About 15.4 km were covered by the wave 40 hours after the flood began.

Table 6. Predicted monthly outflow (m³/s) with respect to current elevation

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Figure 4. Dam breach due to flood wave (time=40 hours)

When the rainfall increased, the overall load in the study region rose. This process causes large amounts of sediment to be transported across river cross-sections together with runoff water from the valleys. The amount of silt transported depends on a number of variables, including bed slop, the amount of water released from Haditha Dam, and the manning coefficient.

The spatial wavelength increase in the HEC RAS simulation occurs 10, 20, 30, and 40 hours after the initial bypass condition, covering 3.8, 5.1, 11.3, and 15.4 kilometers in length (Figure 4).