Benefits of forest conservation on riverine sediment and hydropower in the Tonle Sap Basin, Cambodia

Abstract

Recent deforestation rates in Cambodia are among the world’s largest, while hydropower development has accelerated in the Mekong region. Deforestation accelerates erosion, increasing river sediments heading to reservoirs and decreasing hydropower production. Forest protection could be seen as a service to hydropower, which the FOR-POWER model quantifies. Using recent deforestation estimates, annual sediment accumulation is calculated, followed by associated power generation loss, and annualized and present monetary value associated with benefits of forest conservation to hydropower. We evaluated four proposed medium-size hydropower dams (20–24 MW; 6–145 m3/s design discharge), and found that extensive deforestation could result in annual sediment accumulation of 360–930 million tons (reservoir dependent), but only 140–750 million tons in a forest conservation scenario. Overall, these reservoirs could lose 60–100% of storage capacity over 120 years at current deforestation rates, resulting in power loss net present values for Pursat-I, Battambang I and II dams of US $2.58, $44.8 and $28.8 million, respectively. A global sensitivity analysis showed that FOR-POWER was particularly sensitive to discount rates and electricity prices. The modeling tool developed for this study is transferable to other dams globally where hydropower development is accelerating and in need for better quantifying ecosystem services from surrounding watersheds.