Sediment management in sustainable urban drainage system ponds.

Since removal and disposal of sustainable urban drainage system (SUDS) sediment can incur high maintenance costs, assessments of sediment volumes, quality and frequency of removal are required. Sediment depth and quality were surveyed annually from 1999-2003 in three ponds and one wetland in Dunfermline, Scotland, UK. Highest sediment accumulation occurred in Halbeath Pond, in the most developed watershed and with no surface water management train. From comparison of measured potentially toxic metal concentrations (Cd, Cr, Cu, Fe, Ni, Pb, Zn) with standards, the average sediment quality should not impair aquatic ecosystems. 72-84% of the metal flux into the SUDS was estimated to be associated with coarse sediment (> 500 microm diameter) suggesting that management of coarse sediment is particularly important at this site. The timing of sediment removal for these SUDS is expected to be determined by loss of storage volume, rather than by accumulation of contaminants. If sediment removal occurs when 25% of the SUDS storage volume has infilled, it would be required after 17 years in Halbeath Pond, but only after 98 years in Linburn Pond (which has upstream detention basins). From the quality measurements, sediment disposal should be acceptable on adjacent land within the boundaries of the SUDS studied.