Flow Alteration in the Greater Seattle Area: Causes and Potential Connections to Biological Consequences

As part of various water resource investigations and planning efforts, we have studied the effects of development on stream flow.  The effect of conversion of forest land to suburban and urban land uses (i.e., urbanization) on hydrology has been well documented (here and elsewhere).  The effect of urbanization on stream flow – i.e., increasing peak flows or flow “flashiness” and declining base flows as a result of routing more flow directly to the stream via connected impervious cover – is well established.  However, the effect of water management activities on streamflow – particularly summer baseflow may not be widely appreciated.  Water management activities associated with urbanization in any particular basin include water supply imports and exports and wastewater management (onsite treatment or connection to regional wastewater system).  The basin water balance of these activities has the potential to augment or reduce summer baseflow.  Linkages between hydrologic changes (primarily flow flashiness) and changes in stream biota have been hypothesized.  However, connections between summer baseflow and stream biota still need to be identified.