RAPID ASSESSMENT OF SUSTAINABILITY FOR MULTIPLE WATERSHEDS

This paper presents an approach to assessing the sustainability of watersheds that can be applied by regional authorities to multiple watersheds. It is a GIS/Access database approach that is invaluable in comparing present patterns of water withdrawal and discharge within a watershed to the natural flow cycle in order to assess the degree to which the watershed is stressed.The approach uses a computerized water balance for each watershed, using data in an Access database linked to GIS maps to develop each element of the water balance. The equation used is:ET = P + WW/IND Rech + EDR + SW Disch − RO - SWW − GWW − EDW - BFwhere:ET is the evaporation and transpiration of waterP is the average precipitation at the gage nearest to the subbasinWW/IND Rech is the wastewater and industrial discharge back to groundwaterEDR is the estimated domestic recharge from private septic systemsSW Disch is the discharge of water to creeksRO is the surface water runoff component of precipitationSWW is the withdrawal of water from creeksGWW is groundwater withdrawals from public water supply or industrial wellsEDW is the estimated domestic withdrawal of groundwater from private wellsBF is the median baseflow of streamsThe paper discusses several technical difficulties that were overcome to develop the balances successfully, and shows some of the uses of the water balance results within the water resource plan. The paper also highlights the results of a comparison between net water consumption and two sustainability standards: the Q7-10 and 1 in 25 year low baseflow.