Rainfall - Runoff Process and Modellin for Soreq Stream Subbasin Near Jerusalem

Rainfall - Runoff Process and Modellin for Soreq Stream Subbasin Near Jerusalem

Mazin Husni Barakat The Unit hydrograph and SCS methods were used here to simulate `he runoff coefficient and the, lag time from the mountainous sub-catchment of the Soreq stream near Jerusalem using the data obtained during the period 1957-1994 for frequency analysis and IDF curves. Data ohlained 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 IZafaim streams that flow toward the Mediterranean. The drainage area studied is 167 km2 after excluding the urban area from the stream origin until the Belt 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 internsity for different return periods to be used for drainage systems design. Some of the problem, related to the study area are that the two western outlets of the raw sewage system of Jerusalem, discharge towards Soreq stream. This sewage flov, which is the flow measured at flartov station during the dry periods along the Soceq 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 ~ index was 16.77mm/hr. While the average value of the W index was 3.27rrm/hr. The runoff 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 K,- 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 Rising the equations of the SCS method the average was 334.1 lmin. 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. Mazin Husni Barakat Supervisors Dr. Hafez Shaheen Dr. Anan Jayyousi 2000 Zajel / An-Najah National University