Commonwealth of Virginia Flow-Ecology Project Meeting VDEQ June 23, 2011

Grouping Biological Data Hydrologic Modeling Point

Hydrologic Modeling Outputs Which gauges used, what stream orders What verifications done Natural sites – one hydrograph Altered sites – two hydrographs actual (altered) ‘naturalized’ Calculate IHA parameters and % change (who)

Example Rules – defining the sample unit (‘pour points’) Groupings Use stream flow classes (6) Consider size separation within classes, e.g.: Strahler order 1-3 Order 4-6 Elevation/gradient may also be important

Example Stream Network 1 1 Dots: bio sample sites Numbers: Strahler order X: USGS gauge 2 2 2 3 3 4 Discharge X X

Defining the sample unit (‘pour points’) Minimize extrapolation of hydrologic model beyond its calibration (USGS gauges) Few USGS gauges on streams <2nd or 3rd order Distribution of biological data From NHD+ (1:100,000 scale), samples on 1st to 3rd order

Example Stream Network 1 1 Dots: bio sample sites Numbers: Strahler order X: USGS gauge 2 2 2 3 3 4 Discharge X X

Gauged data– defining the sample unit (‘pour points’) Relation of gauges and biological stations random Several to none in gauged watershed Gauge on segment of same stream order as biological sites (? – hydrologic opinion?) Tribs can come in if order remains unchanged (?) Decision on discharges entering above biological stations Decision on maximum distance between gages and biology

Example Stream Network 1 1 Dots: bio sample sites Numbers: Strahler order X: USGS gauge 2 2 2 3 3 4 Discharge X X

Modeled data– defining the sample unit (‘pour points’) Some pour points may represent several biological points 30-50 data pairs per class