Flood studies in Satluj basin – A research report by National Institute of Hydrology

The study attempts to do flood inundation and flood plain feature mapping as well as undertake river planform measurements for a part of the river reach of Satluj. The river is a part of the Indus system and faces flood during monsoon months in spite of various flood control measures that have been adopted. The vast expanse of land adjoining the river course is inundated by large floods.

A part of the river reach (181 km) downstream of Roopnagar in Punjab is taken up for planform studies, while an upstream stretch of 50 km in the study area was selected for inundation studies. Flood inundation mapping is done for the flood of September 1988 using digital image processing techniques. IRS LISS II digital data and FCC at the scale of 1:250000 are used. Softwares used are Integrated Land and Water Information System (ILWIS) 2.2 and PC-ERDAS 7.5. ILWIS is used in data encoding, image rectification and output. ERDAS is used for image processing and Geographic Information Systems (GIS) manipulation.

The areas on the right flank of the river face greater inundation than those on the left flanks where storage of rainwater occurs in depressions. A flood damage analysis is done by assigning a qualitative damage scale of numbers 1 to 10 in increasing order of damage. The land use, cover and flood inundation map were assigned weights for the analysis. The results will be useful for further investigation in the field and for planning flood control measures.

The percentage of area with low and high flood damage is 2.2 % and 11.9 % respectively. The occurrence of significantly large area under high flood damage class is due to the presence of high area under agricultural land category (90 %). The high damage area may have been overestimated since the crop map for the flood season is not used.

The causes of the floods are overtopping of the banks, floods in the hill torrents and occurrence of low lying areas with poor drainage. The hydrometeorology of the flood of September 1988 and the conveyance capacity of the Roopnagar headworks are also described.

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