Developing Flood Discharge Capacity of Kmait River

Kmait River is a flood escape that was constructed to divert water during flood season from Tigris River to Al Huwayza Marsh through AsSanna'f Marsh. Water stored in Al Huwayza Marsh is then discharged to Tigris River, through Al Kassara River, and to Shatt Al Arab River, through AsSuwayb River. Kmait River, AsSanna'f Marsh, and Al Huwayza Marsh form one hydrological system. Therefore, the capacity of AsSanna'f Marsh and the capacity and operation schedule of Al Huwayza Marsh were taken into consideration when developing the capacity of Kmait River. It was found, by using a one dimensional flow simulation model, that the present discharge capacity of Kmait flood escape does not exceed 80m 3 /sec, and this discharge can’t be diverted completely into Al Huwayza Marsh during January and February months of a wet year unless the discharge capacity of AsSanna'f Marsh outlet is increased from its current capacity of 402m 3 /sec to 468m 3 /sec. It was found that the contraction in last part of Kmait River is throttling the discharge. If this part is reshaped, the capacity of Kmait river will increased to 250m 3 /sec, which could be diverted into Al


1-Introduction
Figure 1 shows Kmait River layout that was designed as a flood escape.This river, with its control structures at Tigris River, Protects Al Am'arah city, Al-Qadissya, Hour Auda, Al-Wadiya, Adel and Al-Izz River irrigation projects from flooding during flood seasons.Tigris River excess water is diverted through this river to Al Huwayza Marsh.Diverted water is stored in Al Huwayza Marsh and discharged to Tigris River through Al Kassara River and to Shatt Al Arab River through AsSuwayb River Kmait River intake structure is located at just 5km north of Kmait Village.The design capacity of this structure is 400m 3 /sec, [1].The crest level of the escape is 8m amsl.The escape structure consists of 27 gates each has a width of 3.5m.The upstream and downstream sill levels are 8 and 6m amsl, respectively.. The total length of Kmait River from its intake to AsSanna'f marsh is 36Km.The river's flood dikes elevations vary between 10.5 and 11m amsl.No studies are available to show whether this river can discharge the design discharge of the control structure or not.
Water delivered by Kmait River is discharged into AsSanna'f Marsh and then to Al Huwayza Marsh.The minimum level of the dykes surrounding the southern part of Al Huwayza Marsh, between the marsh outlets, is 7.5m amsl.The maximum surface area of Al Huwayza Marsh is 1800km 2 with storage capacity of 5900 million cubic meters and the maximum discharge capacity of its outlet is 325m 3 /sec.The maximum surface area of AsSanna'f Marsh is 360km 2 with storage capacity of 750 million m 3 .The present maximum discharge capacity of its outlet is 402m 3 /sec.
The minimum level of the dykes surrounding the southern part of AsSanna'f Marsh, near Al Msharah River is 9m amsl.Hydrological routing of AsSanna'f Marsh shows that the minimum level of the dykes surrounding the marsh must be11 m amsl to prevent the flood which occurs during the wet years and the maximum storage and surface area of the marsh will be 1480 million cubic meters 426Km 2 , respectively [4].
In addition to Kmait River, AtTeeb River, Dwayreach River, and the surface runoff of Ashmasher area are the main feeders of AsSanna'f Marsh.

2-Present Capacity of Kmait River
To examine the hydraulic performance of Kmait River under various flow rates, a steady one dimensional flow routing hydraulic model was prepared using HEC-RAC software, [5], and was used to simulate the flow along Kmait River.
Fifty seven cross sections were used in the model [6].The upstream boundary condition is a constant discharge while the downstream boundary condition is a normal depth.
Due to the nature of Kmait River, a varying Manning roughness coefficient was used along the river, starting with 0.03 and is increased to 0.045 at the end of the river.Discharge value at the upstream end was varied from 10 to 150m 3 /sec to check the present capacity of this river.The resulting longitudinal water surface profiles for these discharges are shown in Figure 2. It is clear from this Figure that the maximum capacity of the river under the present condition is 80m 3 /sec, otherwise the water level will exceeds the level of the river flood dykes.This limitation in the capacity of Kmait River is due to the contraction at its end, as shown in Figure 3, causing a throttling to the discharge and rising the water level.To make use of Kmait flood escape maximum capacity during January and February months, which could be absorbed by Al Huwayza Marsh, the maximum capacity of AsSanna'f Marsh outlet should be developed to be 468m 3 /sec.
The control structure must be operated according to the maximum allowable monthly inflows from Kmait escape, Table 3.
Table 1 shows the monthly discharge of these feeders and that at the outlet of AsSanna'f Marsh during a wet year, and the discharge at outlet of AsSanna'f Marsh required to Eng. & Tech.Vol. 26, No.9 , 2008 Developing Flood Discharge Capacity of Kmait River