Erosion of agricultural croplands is a significant contributor of sedimentation to reservoirs. Here, physiographic and economic models for a large agricultural watershed (2377 square miles with 27 subwatersheds) are integrated for the reduction of sedimentation of one Midwestern reservoir. Sediment reduction and the cost-effectiveness of three agricultural best management practices (no-till, filter strip, and permanent vegetation) implementation were considered under three modeling scenarios: random assignment; the globally most cost-effective approach; and a cost-effective targeting approach. This study demonstrates how physiographic and economic data can be harnessed to yield readily comprehendible cost-effective targeting maps. Cost-effective targeting may be preferable to watershed managers for its “user-friendliness” without too great a sacrifice of the globally most cost-efficient solution.

The operation and longevity of hydropower dams are often negatively impacted by sedimentation. Forest conservation can reduce soil erosion, and therefore efforts to maintain upstream forest cover within a watershed contribute to the economic life span of a hydropower facility. The cost of forest conservation can be viewed as an investment in hydropower and be financed via a payment for ecosystem services (PES) scheme. A novel modelling framework is used to estimate payments for forest conservation consisting of: (1) land-use change projection; (2) watershed erosion modelling; (3) reservoir sedimentation estimation; (4) power generation loss calculation; and (5) PES scheme design. The framework was applied to a proposed dam in Cambodia (Pursat 1). The estimated net present value of forest conservation was US$ 4.7 million when using average annual climate values over 100 years, or US$ 6.4 million when considering droughts every eight years. This can be remunerated with annual payments of US$ 4.26 ha−1 or US$ 5.78 ha−1, respectively, covering forest protection costs estimated at US$ 0.9 ha−1 yr−1. The application of this type of PES represents a rational option that allows for conservation and development of hydropower watersheds susceptible to erosion and sedimentation.

Reservoir sedimentation provides a valuable source of data on sediment flux. This paper assesses the record of sedimentation in the Baldernock Mill dam, a small mill dam in western Scotland. That record is based on the volume of sediment in the dam, and the detailed analysis of a continuously sampled stratigraphic section through the impounded sediment, with a chronology for mill dam construction and subsequent breaching based on historical maps and the impounded sediment’s content of 137Cs and lead isotopes. The mill dam was constructed in c. 1820, was initially partially breached in the late nineteenth or early twentieth century and then fully breached by about the mid 1920s. The dam trapped relatively low volumes of sediment and the correspondingly low rate of sediment flux indicated by the volume of impounded sediment reflects the dam’s very low trap efficiency. The basal Unit 1 in the impounded sediments was deposited between dam construction and the initial breaching of the wall. The unit consists of repeated ‘triplets’ of a basal sand (flood deposit) grading upwards into a mud deposit (post-flood deposition), which is in turn overlain by an organic-rich layer of leaves and twigs (the subsequent autumn leaf fall). Unit 2 is similar to Unit 1 but lacks the organic layer, indicating the lack of ongoing standing water to trap the autumn leaf fall, and Unit 3 was deposited after full breaching of the wall. Mill dams in Scotland generally impound small steep bedrock channels – the latter reflecting a strong glacial legacy in Scotland – and are only small structures designed to ensure water for mills during dry periods in a climate of otherwise generally moderate to high and reliable rainfall. The small sizes of these dams and their low wall heights mean that they trap relatively low volumes of sediment that have minimal to minor downstream impacts if the dams fail.