The sediments on the floors of nine reservoirs in the Midland Valley of Scotland have been examined to establish rates of sedimentation and catchment sediment yields. Information from Cullaloe, Drumain, Harperleas and Lambieletham Reservoirs (Fife), is compared with data from Glenfarg and Glenquey Reservoirs (Tayside) and earlier studies on Hopes, N Esk (Lothian) and Kelly (Strathclyde) Reservoirs. The earth-fill dams were constructed between 1850 and 1935 below catchments ranging from 1·53 to 23·5 km2 in area. They are situated on sedimentary, volcanic or intrusive igneous rocks mainly of Devonian or Carboniferous age. In most areas bedrock is obscured by mantles of drift. Six of the catchments are dominated by moorland terrain with local afforestation. Mixed arable farming and woodland characterise the remainder. The higher basins receive on average over 1400 mm of precipitation per annum, while in the lower basins some 800 mm falls.

Measurements of thickness variations of the deposits have enabled the construction of isopachyte maps from which the volumes of entrapped materials have been derived. The computed catchment sediment yields vary from 2·l t km−2 yr−1 (Lambieletham) to 52·0 t km−2 yr−1 (Glenfarg). Sediments incorporate both mineral and organic matter, of which combustible material commonly forms 15–20% by weight. Siliceous tests of diatoms are also an important component of the deposits. The sediment yields computed are about an order of magnitude greater than those reported from rivers draining similar sizes of catchment within the Forth basin. There is a direct relationship between mean annual inflow to the reservoirs and sediment yield.