In comparing the flow reduction required to produce a 15% spatial loss with the flow

reduction required to produce a 15% temporal loss, it was found that a 15% temporal loss

occurred consistently at a smaller reduction in flow (Figure 3-5). This does not specify in an

ecological sense how the two different measures relate though it does indicate that, on these three

rivers, the temporal measure is more conservative with respect to protection of natural flows.

 Summary

 For determination of MFLs the District has chosen the measure of temporal loss as a

measure of habitat change. This analysis requires that the relation between the target elevation at

a specific point in the river corridor and the flow at a long-tem gage is reasonably well

understood. It also requires long-term gage data. The spatial analysis requires the acquisition of

cross-sections and the development of a model to calculate the habitat loss. The resolution of the

cross-sections and the use of top-width as a proxy for inundated area limit the accuracy of the

analysis. For rivers currently being studied for MFL development improved topographical data

(i.e., LiDAR) is being collected. This will allow the development of digital elevation models and

improved spatial analysis of floodplain inundation. Comparisons of these improved methods

with the current methods should be performed. As instream flow professionals we are often

asked to protect the environment from harm. However, ultimately what is measured is change

and how much change constitutes harm must be determined. Therefore, we must know how

different measures of change relate to each other.