AECOM Report B&W - N - City of Guelph

City of GuelphAppendix G - Water Budget 2008Appendix GWater Budget Summary for GuelphMeteorological data for the GRCA meteorological station at the Guelph Dam collected during 2008 havebeen reviewed with long term data (collected since 1984) from the same location to prepare a water budgetfor Guelph for 2008.The 2008 annual precipitation Guelph was 1,252 mm. On average, the 20 year (1984-2003) annualprecipitation at the Guelph Dam is 881 mm. The distribution of the precipitation is shown in Figure G1,together with the average results. 2008 was significantly wetter than normal, with the summer months beingsignificantly wetter, most noticeably July (Figure G1). During this month a surplus was actually recorded,when usually a deficit occurs. This high precipitation observed was related to several heavy storm eventsthat occurred throughout the summer of 2008.A Water Balance has been prepared for using the method described in Thornthwaite and Mather (1957).The 2008 evapotranspiration is calculated to be 585 mm, based on assumed soil moisture storage of 100mm. The normal evapotranspiration has been estimated to be 566 mm.The 2008 annual water surplus is calculated to be 667 mm, compared to a normal surplus of 316 mm. Thewater surplus comprises of both the surface runoff and infiltration components of the water balance. Sitespecific conditions like soils and topography need to be evaluated in order to partition the surplus intosurface runoff or infiltration.Reference:Thornthwaite C. W., and J. R. Mather, 1957:Instructions And Tables For Computing Potential Evapotranspiration And The Water Balance; DrexelInstitute of Technology, Laboratory of Climatology, Publications In Climatology, Volume X, Number 3, 1957,311 pp.I(111414_2ra-apr29-09_appg.doc) - G1 -