Forest Fish Project

The presence and location of groundwater discharge zones used as brook trout spawning and nursery habitat have been related to presence of coarse overburden material in discharge zones and to local topography. However, data on hydrogeologic conditions in lake watersheds are frequently unavailable, while their field evaluation for specific sites is costly and time consuming. An alternative approach is provided through the use of digital elevation models to derive topographic indices (TIs) that can predict the relative potential for groundwater discharge at various locations along the land-lake interface.

This Figure presents a widely-used example of a topographic index (TI), where a is the upslope area (green cells plus the area of the red cell) draining to a particular cell (red cell) in a digital elevation model and b is the slope angle of the particular cell of interest (red cell). It incorporates the role of both plan and profile convergence (discussed earlier) in promoting discharge of subsurface water to the ground surface. Such indices have been used successfully to predict the location of surface saturated areas, water table elevations and subsurface flow conditions. The TI can be used to represent the relative likelihood of saturation of the overburden at a given location by subsurface flow from further upslope and the discharge of subsurface flow to the ground surface. Spatially-distributed values of TI can be readily obtained from digital elevation models.