Surface Water Yield Assessment: Final Report

February 2001

Executive Summary

A consortium consisting of SEPA (Scottish Environmental Protection Agency) and DoE (Northern Ireland) acting in collaboration as SNIFFER (Scotland and Northern Ireland Forum For Environmental Research) - and the three Scottish Water Companies commissioned Water Resource Associates to develop and supply software for the simulation of water resource systems in the region.

The software was intended to implement a consistent methodology for the estimation of runoff in rivers, emulation of complex sets of linked water resource system components, and simulation of system performance. It was to take particular account of the region's important hydrological characteristics such as the relative frequency of snow at altitude, the extent of peat etc.

A software package known as Aquator-HYSIM was developed for the purpose. It is an integration of HYSIM - a catchment model of many years standing which was developed and extended to meet the required hydrological criteria - and Aquator - a powerful state-of-the-art system model developed by collaborators Oxford Scientific Software in part from predecessor programs but incorporating many innovative features.

The package is designed to run with any time series of rainfall and evaporation data but, for a consistent approach to yield estimation, it is likely that historical data from the period 1918 to 1998 will be used. To this end, a procedure for computing potential evapotranspiration between those dates at any location in the region was developed.

The procedure was tested at four sites in Scotland (the River Dee, Loch Lomond, Loch Bradan and the Meggett-Talla-Fruid scheme. In each case, historic rain data were assembled and PET data computed. HYSIM was calibrated using gauged river flow records and an Aquator representation of the water system was developed. This work is reported in detail in a companion volume ‑ the Trial Sites Report.

The possibility of using stochastically-generated rainfall series (instead of historic) was reviewed but not recommended.

The Project was overseen by the clients through ten quarterly progress meetings with the Contractors. A corresponding series of ten reports (9 Progress reports and an Interim Report) recorded the detailed work of the Project team. This Final Report is, in part, a distillation of these earlier reports.

The software package with supporting climate data and hardcopy documentation were delivered to the clients in February 2001.

Copies of this report are available from the Foundation, price 15.00, less 20% to FWR members