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ABSTRACT: Estimation of peak floods in a watershed where industrial and housing development is present always has prime importance to determine extent of flooding and its damage. Such type of estimation guides that these developments are safer during flooding or not. So an valley is one of the important valley in which major cities like Rawalpindi, Attock and a part of Islamabad is located. This study is based on long term recorded flood data along the Soan river at various locations. Detailed flood frequency analysis was carried to select the best fit frequency models at various locations in Soan river. The data were processed to check its consistency and outliers. The estimated peak of the floods in Soan at Chirah, Rawalpindi and Dhok Pathan for 100 year return period worked out to be 3787, 5752 and 9842 m^sup 3^/sec respectively. These results may be helpful for future development along the river by determining the elevation of flood encroachments along the banks.
Key word: Peak floods, flood frequency, outliers, catchment, gauging stations, return period.
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INTRODUCTION
Estimation of flooding in Soan valley has great importance, because the river crosses Rawalpindi and Attock districts where a lot of industrial and housing development along the river banks has been made. Soan river is one of the left bank tributary of Indus river. It lies between Longitude 71° 45' to 73° 355 and Latitude 32° 45' to 33° 55'. This study may be useful to determine the extent of flooding and its damage in the area.
The Cathment Area: Soan valley is a part of Potohar Plateau, lies to the south of northern mountains. (Figure1). Soan river originates from Muree hills and passing through the steep slopes (about 3.78 %), it enters the plains near Chirah. Simly dam is located 13.9 km upstream of Chirah on Soan river. Rawal dam on Soan is situated near capital Islamabad. Four major streams Ling river, Korang river, Sil river and Lai nullah contributes flood to the Soan River. Total length of main river is 274 km. (Jehanzeb, 2004) The catchment area upto Dhok Pathan gauging station is 6475 sq km.
The area has 305-610 m...