Biogeoclimatic classification system for hydrologic interpretations

Abstract

The purpose of this study was to assess the utility of the biogeoclimatic land-classification system for hydrologic interpretations. It was hypothesized that hydrologic recharge and discharge areas could be identified in a watershed using biogeoclimatic survey data. An intensive biogeoclimatic survey was conducted in Tri Creeks Experimental Watershed, which is located 70 km southwest of Edson, Alberta. Plant associations identified by the survey were evaluated as either recharge or discharge areas based on species composition, slope position, relative water yield, soil-water storage, and peak-flow estimates based on a modified form of the rational equation. The biogeoclimatic survey identified two distinct plant associations. Each plant association was characterized by four to six indicator species. Genera for plant association A included Geum, Salix, and Betula, and those for plant association B included Arnica, Cornus, and Vaccinium. Plant association A was considered representative of discharge areas because of its location on lower slopes adjacent to stream channels, and the presence of plant species indicative of wet riparian habitats. Association B was judged a recharge area because of its location on upper slopes and the presence of plant species indicative of drier habitats. Simple water-balance calculations for each plant association further supported these interpretations. The greater relative water yield and soil-water content throughout the growing season for association A over association B were judged a reflection of its location in a discharge area. The prediction of peak flows, using the areal extent of association A in the rational equation, also supported its identification as a discharge area. The precision of prediction was low with estimated values exceeding actual values by 1–4 times. However, moderate to high levels of correlation between estimated peaks and actual peaks were observed for late-summer storms, and judged to demonstrate the importance of association A as a discharge area for storm flow.