Rainfall-Runoff Process and Modeling for Soreq Stream Sub-Basin Near Jerusalem

Discussion Committee: 
Dr. Hafez Shaheen
Dr. Anan Jayyousi
Dr. Issam A.Al-Khatib
Dr. Numan Mizyed
Dr. Hafez Shaheen
Dr. Anan Jayyousi
Mazin Husni Barakat
The Unit hydrograph and SCS methods were used here to simulate the runoff coefficient and the lag time from the mountainous sub-catchment of the Soreq stream near Jerusalem using the data obtained during the period 195-1994 for frequency analysis and IDF curves. Data obtained during the period 1994-1996 were used for the rainfall-runoff analysis. The investigated area is situated near Jerusalem in the watershed of the Soreq and Rantim streams that flow toward the Mediterranean. The drainage area studied is 167 km2 after excluding the urban area from the stream origin until the Beit Zayit (dam) reservoir. Intensity-Duration-Frequency curves were developed for this area by analyzing the historical data of the two rainfall stations using the Gumbel distribution. These curves can be used as a reference for the determination of rainfall intensity for different return periods to be used for drainage systems design. Some of the problems related to the study area are that the two western outlets of the raw sewage system of Jerusalem discharge towards Soreq stream. This sewage flow which is the flow measured at Hartov station during the dry periods along the Soreq stream is considered as a base flow all along the study. According to these measurements, considerable amounts of sewage water infiltrate along the Soreq stream. Representative events were analyzed during the study period in order to have an indication of the real amount of excess rainfall that causes the runoff.For each event the area under the direct runoff hydrograph (Vd) was calculated for the derivation of the excess rainfall. For the infiltration rate, the ¢ and W index methods were used. The average value of the Ø index was l6.77mm/hr. While the average value of the W index was 3.27mm/hr. The run off measured was about 0.3 % of the measured rainfall due to the high percolation rate into the karstic layers of the area. On the other hand, for each event the recession constant Kr, was evaluated .The average value of this constant for the above events was 0.9925. Unit hydrographs for these events were obtained. Each unit hydrograph of the above events have a different duration. The lag time measured for these events has an average of 609.25min, while using the equations of the SCS method the average was 334.11 min. This situation arises the problem of the sewage flow along the stream, which makes the runoff including the sewage deposits flow slowly towards the outlet. These results may be approximated by assuming that the lag time of this watershed equals the time of concentration, instead of 0.6 of the time of concentration as the SCS method suggests.
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