Post-landslides in Kodagu, sedimentation at Harangi dam increases by 100 times

Kodagu Connect News Network

MADIKERI: Other than causing huge loss in terms of infrastructure, property and crops, the recent floods and landslides in Kodagu have led to indirect losses that are long-term and complex. For example, these landslides have brought significant sediment load in the drainage channels and connected water reservoirs

One such impacted reservoir is the Harangi dam, which is located close to the northern affected areas near Kushalnagar. Using pre-landslides and post-landslide open source satellite images and advanced GIS image processing, WRI India generated map showing Total Suspended Solid (TSS) concentration within the Harangi reservoir has increased by almost 100 times due to flow of increased load of soil and sediment within the reservoir. It is believed such high load of soil and sediment inflow causes sedimentation within the reservoir and thereby significantly reduces the water holding capacity of the dam.

Silting is a natural hydrological and sedimentological process in which sediments flowing from the upstream catchment area get deposited in the reservoir.

Harangi dam is the main catchment area of River Kaveri in Kodagu. The dam can store up to 8.5 tmcft of water and has the potential to irrigate 54,591 hectares of command area in Somwarpet, K.R. Nagar, Arkalgud, Hunsur and Periyapatna taluks. Water from the dam helps cultivation of over 18,000 tonnes of paddy in the region.

The colour of water at Harangi dam has turned muddy post-landslides. (Photo: Chandra Mohan)

In his response to Kodagu Connect, Raj Bhagat Palanichamy, Senior Project Associate, WRI India, said, “Since most of the erosion and landslides happened upstream, the soil that was washed away by the water entered Harangi dam. Using satellite images from European Union – Copernicus Programme and a processing method called C2RCC process, we calculated the total suspended solids in the Harangi dam (before and after the deluge). This is based on the clarity (reflection of light) in the water surface. After the landslides, we found that the solids (sediments) from the river had increased by nearly 100 times due to the erosion. All these sediments would be now settling in Harangi dam. Apart from reducing the capacity of the dams, these sediments would also cause structural troubles for the constructions in rivers like weirs, dams, bridges.”

Speaking to Kodagu Connect, a source at Harangi dam, said, “Soon we will undertake a survey to determine the increase in sedimentation rate in the reservoir due to landslides in catchment area. If we find a drastic increase in silt which might affect storage capacity of the dam, then de-silting measures will be initiated.”

(Source: WRI India, contains modified Copernicus Sentinel data [2018]; Processed by Raj Bhagat P, Samrat Basak)

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