Lai Nullah
Lai Nullah (Urdu: نالہ لئی), commonly called Nullah Lai, is a rain water fed natural stream flowing through the city of Rawalpindi. Every monsoon season the stream floods after being fed by its catchment basin in the Margalla Hills bordering Islamabad, Pakistan.
The Lai Nullah Basin has a catchment area of 234.8 km2, extending to the twin cities of Islamabad and Rawalpindi.
A record level of 620 mm of rainfall fell in Islamabad, Pakistan one in just 10 hours brought in its wake huge urban storm flooding in the famous Lai Nullah flowing through the twin cities on 23 July 2001., Islamabad and Rawalpindi are situated along the Margallah hills. In this paper severe rainfall spell 4–9 July 2008 is analyzed. Our main focus is the flooding which occurred on 5 July due to 104mm rainfall received in only 100 minutes; 162 mm rainfall was recorded only in 5 hours at PMD Headquarters Islamabad. Densely populated low-lying areas along Lai Nullah faced flood like situation causing massive destruction of property and life. Three people died in the flash flood. It was the heaviest short period rainfall in last six years, reminding the cloud burst of 23 July 2001. Temporal coincidence of July 2001 and July 2008 shows that both the events occurred between 00-09 UTC. The Nai Nullah river has six major tributaries, three originating in the foothills of Islamabad in the higher plain area; it then flows down through the lower lying city of Rawalpindi, where another three tributaries join the river.
Lai Nullah starts from the IJP Road in Islamabad at the administrative boundary between the twin cities of Rawalpindi and Islamabad. Apart from flow from Islamabad area, 11 main drains of Rawalpindi City also contributes to Nullah Lai. REF RDA DOC
The Lai Nullah combined with its tributaries such as Saidpur Kasi, Kanitwali, Badarwali Kasi and Tenawali Kasi, originating from Margala Hills enter in Rawalpindi city from CDA area at IJ principal Road and Khayaban-e- Sir Syed. The additional tributaries including Niki Lai, Dhoke Hassu Nullah, Dhoke Ellahi Bakhash and PAF Colony Nullah join the main stream of Lai Nullah within Rawalpindi City. REF RDA DOC
The climate of the Lai Nullah Basin area is classified as “Subtropical Triple Season Moderate Climate Zone”, which is characterized by single rainfall season from July to September and its moderating influence on temperature. The case Study area has hot summers and cold winters. In June the daily maximum temperature reaches to 40 °C, while the daily minimum temperature falls near to 0 °C in December and January. Between July and September, the temperature is slightly moderate due to humidity. The case Study area receives rains in all seasons but monsoon rain is pronounced and constitutes a definite rain season but monsoon between July and September. The total rainfall during the rain season is about 600 mm, accounting to 60% of the annual rainfall of about 1,000mm.
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