The importance of sediment characteristics and trap efficiency in assessing sediment yield using retention ponds

Retention ponds are a valuable tool for assessing sediment yield (SY) over large areas. SY is normally expressed in t ha(-1) a(-1) or t km(-1) a(-1) a nd therefore measured sediment volumes in ponds need to be converted to mas ses using representative values for the dry bulk density (dBD) and correcte d for trap efficiency (TE). Mean dBD varied from 1 to 1.35 t m(-3) for eigh t retention ponds in central Belgium. Within the Hammeveld retention pond, dBD ranged from 1.14 to 1.58 t m(-3) with a mean value of 1.34 t m(-3). Var iations in dBD are mainly controlled by texture and the length of dry perio ds between rain events. Values of TE were calculated for this pond by compa ring soil losses due to water erosion in the catchment with sedimentation r ates in the pond. TE varied between 58% in spring-summer and 96% in autumn- winter because of different hydrological conditions. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.