High flow aggregate hazard values and low aggregate buffer hazard values suggested the presence of a mitigating land cover pattern near a habitat area separating a more distant flow-related hazard. The reverse scenario indicated areas with particularly small flow zones or ones where the preponderance of the drainage land cover varied significantly from the immediate surroundings. The decision to use uphill flow delineation instead of the watershed polygons produced by the ArcView hydrology tool or the Washington State DNR defined Water Resource Inventory Areas proved critical. In an effort to evaluate whether this method would lead to different hazard ratings than those which could be obtained by basic watershed assessment, we examined all areas with high aggregate hazard values in all categories and compared these to nearby habitats that did not result in high hazard values. Finally road coverage added depth and distinction to our evaluation in both spatial units of analysis.
Roads are highly influential forces affecting ecological systems.
Most importantly, they may be overlooked when remotely sensed land cover data is the sole basis for evaluating the influence of land features on habitat areas. Use of this method allowed the team to identify threatened areas in less urbanized areas where rural roads or forest road construction has a powerful influence. In the DEM, lowland and coastal cells often contained no data, complicating flow zone delineation for coastal wetland habitats. The effect is the artificial truncation of flow zones for coastal habitat areas and estuaries, an important problem that effectively biases analysis in unpredictable ways. The method's reliance on means of cellular values or segment lengths normalized by analysis zone area may favor the identification of habitats with small flow zones.