1. Stream flow estimation

2. Why try to estimate it? Gauges don’t exist on every stream Important for water quality modeling Permitting discharge sites Biological importance Recreation Flood forecasting Influenced by human factors More USGS gauges are now off-line

3. Drainage Area Weighting

4. STREAMSTATS

5. STREAMSTATS

7. 7 Using drainage area to estimate stream flow More of a “back of the envelope” approach Uses ratio between drainage area and gauged flow to estimate flow Assumes stream flow is the same per unit area as a nearby gauge Best for sites near gauged locations (ratio.3 to 1.5) and in the same watershed Gauge Drainage area = 50 Upstream Sites Drainage area = 15 Downstream Site Drainage area = 75 Area good to go for estimating flow with the ratio method!

8. Steps for ratio method 1.Find USGS gauge location downstream and in the same watershed 2.Summarize the recorded flow from gauge (USGS web site) 3.Find the FAC values at gauge and location of interest 4.Apply ratio of flow to drainage area at gauge to all upstream drainage areas in the FAC grid

9. Application to the Big Sandy

10. http://waterdata.usgs.gov/nwis

11. Mapper

12. Mapper

13. Stream flow info

14. ArcMap

15. ArcMap

16. ArcMap

17. Drainage area calculation 5,169,555 FAC units FAC * cell size squared = Drainage area in meters squared (10 * 10) = 516,955,500 meters squared or = 127,781 acres or = 199.65 square miles ~ 200 square miles

18. Stream flow info

20. Example Rockville gauge on the Big Sandy has a drainage area of 5,169,555 FAC units and an instantaneous flow of 226 cfs Drainage area value -------------------------------------------- Measured or recorded flow cfs Drainage area value at a site ----------------------------------- Flow at a site in cfs = 5,169,555 ------------------- 226 Flow FAC = ------------------- Cross multiply… Flow * 5,169,555 = FAC * 226 Flow = USGS Gauge Info: Ungauged location of interest: ------------------- 5,169,555 FAC * 226

21. ArcMap

22. Are we done?

23. Revised legend for ratioflow

24. Converting grid to lines

25. Possible extent that can use ratio method

26. Hydrological limitations Lack of interception, evapotranspiration, baseflow from groundwater Distribution of a rainfall event

27. Application limitations Best when applied to the same stream as the gauge within.5 to 1.5 of gauge DA. Can go down to.3 and into side tributaries but estimate is less reliable. Limited to natural systems (no dams or impoundments)

28. Questions / comments?