| Abstrakt: |
The river Krishna originates in the Western Ghats of the State of Maharashtra in India. It flows through the Satara, Sangli and Kolhapur districts of Maharashtra, before meeting the Bay of Bengal. In 2019, widespread heavy rains occurred from 28th July to 12th August in the Krishna basin resulting in a flood situation. The flood situation started aggravating from 1st August and reached its worst on 8th, 9th and 10th August. Almost 2/3rd of the Sangli and Kolhapur districts were underwater for more than 10 days. The major flood-prone spots are Sangli, Kolhapur and Rajapur, which receive floods from free as well as dam intercepted catchments. There are 22 dams in the basin upstream of the above three spots on various tributaries. These dams have major storage below spillway crest and minor above it, against operatable gates. Dams across rivers, whether they create or absorb floods, have always been an issue of debate. This paper presents a study of the impact of flood releases from various reservoirs in the Krishna basin from 30th July to 17th August 2019, along with the role played by three major dams, i.e. Koyana, Warna and Radhanagari. An ideal condition without dams is studied to assess the effect of reservoirs on downstream floods of the region. The study reveals that during the above period, average flood values at Sangli and Rajapur have more contributions from free catchment areas, rather than dam spills. However, in critical flood situations from 6 to 9th August 2019, the major contribution in flood was from unavoidable dam spills. The flood absorption capacity of dams is classified into two stages. Stage I is till the water level reaches spillway crest level. Stage II is after the water level rises above spillway crest level and water is stored/released against gates. In Stage I, the upstream dams absorbed 3072 Mcum of water, mitigating the disaster in the flood-prone area. In Stage II, the peak discharge values were reduced for Koyna and Warna dams by 19% and 32%, respectively. Also, the peaks were delayed by 2 days which contributed to flood mitigation. In the analysis of the condition (Without Upstream Dam Condition), the situation would have created an adverse impact on the flood-prone area. |
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