Abstract
The current study investigated the impact of constructing the Auxiliary Kandar Dam on the Main Kandar Dam reservoir's effective lifespan in District Kohat, Khyber Pakhtunkhwa, Pakistan. Storage capacities were assessed through a grid survey, with computer software (SURFER) used for calculations. Sediment yield was determined using the HR Wallingford yield prediction Model (WSYPM). The capacity of Main Kandar Dam reservoir was 1,000,365 m³, while the Auxiliary Kandar Dam's capacity was 1,994,974 m³. Over 9 years, 196,654 m³ of sediment was deposited into the Auxiliary Kandar Dam reservoir, leading to a 9% reduction in its storage capacity. Main Kandar Dam exhibited a trap efficiency of 90.48%, which decreased with the inflow ratio dropping from 0.508 to 0.194. In 6 years, 175,501 m³ of sediment was deposited into Main Kandar Dam reservoir, resulting in a 61.78% reduction in its capacity over 41 years. Observed sediment rates for both reservoirs closely matched the WSYPM-predicted values. The construction of the Auxiliary Kandar Dam in 2014 extended the Main Kandar Dam's effective life by 34 years (2022–2056). Additional construction in 2016 or 2022 could further extend the lifespan by 80 years (2022–2102) or 68 years (2022–2090) respectively. If the left Auxiliary Dam is built in 2025, the Main Kandar Dam's life is anticipated to increase by 66 years (2022–2088). This option would extend the lifespan by 65 years beyond the current estimate, projecting a total life from 1972 to 2079 as 107 years.