Appendix A: Streamflow Estimation Techniques
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TMDLs for the White Oak Creek Watershed Appendix A: Streamflow Estimation Techniques Final Report TMDLs for the White Oak Creek Watershed Contents A-1 Introduction .................................................................................................................................. A-2 A-2 Drainage Area Weighting ............................................................................................................ A-3 A-2.1. Data ..................................................................................................................................... A-3 A-2.2. Analysis ............................................................................................................................... A-4 A-3 Linear Regression ........................................................................................................................ A-7 A-3.1. Data Preprocessing .............................................................................................................. A-7 A-3.2. Developing a Linear Regression ......................................................................................... A-7 A-3.3. Testing the Final Linear Regression .................................................................................. A-11 A-4 ILSAM ....................................................................................................................................... A-15 A-4.1. Little Wabash River .......................................................................................................... A-15 A-4.2. Equation Parameters for White Oak Creek ....................................................................... A-15 A-4.3. Analysis ............................................................................................................................. A-19 A-5 Summary .................................................................................................................................... A-26 A-6 References .................................................................................................................................. A-27 Figures Figure A-1. Station locations .................................................................................................................... A-4 Figure A-2. Predicted versus observed data at stations 300057 and X02W06 ......................................... A-6 Figure A-3. Linear regression of discharge data. ...................................................................................... A-8 Figure A-4. Linear regression of standardized discharge data. ................................................................. A-9 Figure A-5. Linear regression of standardized instantaneous discharge data. ........................................ A-11 Figure A-6. Accuracy testing of the linear regression. ........................................................................... A-13 Figure A-7. Linear regression estimation error. ...................................................................................... A-14 Figure A-8. SSURGO representative hydraulic conductivity at saturation at maximum depth. ............ A-17 Figure A-9. SSURGO maximum hydraulic conductivity at saturation at maximum depth.................... A-18 Figure A-10. ILSAM at USGS gage. ...................................................................................................... A-19 Figure A-11. ILSAM flow-duration curve for station 300057. .............................................................. A-21 Figure A-12. ILSAM flow-duration curve for station X02W06. ............................................................ A-22 Figure A-13. ILSAM flow-duration curve for station X02W05. ............................................................ A-23 Figure A-14. ILSAM flow-duration curve for station X02K17. ............................................................. A-24 Figure A-15. ILSAM flow-duration curve for station X02K15. ............................................................. A-25 Tables Table A-1. Ohio EPA sample stations with instantaneous discharge data. ............................................... A-3 Table A-2. Drainage area ratio method prediction for station 300057. .................................................... A-5 Table A-3. Drainage area ratio method prediction for station X02W06. .................................................. A-5 Table A-4. Standardized log data for the final linear regression. ........................................................... A-10 Table A-5. Estimating instantaneous discharge with the linear regression. ............................................ A-12 Table A-6. ILSAM estimation accuracy at gage 03238500. ................................................................... A-20 Table A-7. ILSAM estimation accuracy at station 300057. .................................................................... A-20 Table A-8. ILSAM estimation accuracy at station X02W06. ................................................................. A-21 Final Report A-1 TMDLs for the White Oak Creek Watershed A-1 Introduction Flow data are not available for the listed section 303(d) segments; although, there is one active USGS gage in the watershed. Thus, a streamflow estimation technique is necessary to create flow duration curves at the assessment points for each impaired waterbody. Additionally, streamflow estimates are also needed as part of the data assessment process using a duration curve framework. Three streamflow estimation techniques were analyzed for this report: drainage area weighting, linear regression, and ILSAM. The results showed that only the ILSAM method yielded acceptable results. Final Report A-2 TMDLs for the White Oak Creek Watershed A-2 Drainage Area Weighting Drainage area weighting is a widely used technique in many cases where limited streamflow monitoring data are available. This method is most valid in situations where watersheds are of similar size, land use, soil types, and experience similar precipitation patterns. Discharge is estimated by drainage area weighting using the following equation: Aungaged Qungaged Qgaged Agaged where Qungaged: Flow at the ungaged location Qgaged: Flow at surrogate USGS gage station Aungaged: Drainage area of the ungaged location Agaged: Drainage area at surrogate USGS gage station A-2.1. Data The accuracy of this method was tested using the instantaneous discharge data collected by Ohio EPA at stations X02W06 and 300057 (Figure A-1) during the summer of 2006. The drainage areas of the two stations are 29.7 and 53.6 square miles (mi2), respectively (Table A-1). Table A-1. Ohio EPA sample stations with instantaneous discharge data Number of River mile Drainage area discharge Station ID Station name Stream name (miles) (mile2) samples @ CR-24B North Fork 300057 1.48 53.6 10 (Tri-County Hwy) White Oak Creek @ Sterling Road at X02W06 Sterling Run 0.59 29.7 12 South Ford Final Report A-3 TMDLs for the White Oak Creek Watershed Figure A-1. Station locations. USGS operates a gage on White Oak Creek (03238500) near Georgetown (Figure A-1). The gage has a drainage area of 218 square miles and a period of record of October 1923 to November 1935 and October 1939 to present. Mean daily discharges were downloaded from the National Water Information System (USGS 2008b). Hourly data at this gage were downloaded from Instantaneous Discharge Archive (USGS 2008a). Hourly data for 03238500 were not available on August 7, 2006, August 9, 2006, and September 8, 2006, because the gage was not operating properly (Koltun, hydrologist, USGS, email correspondance, June 2008). Mean daily discharges for these dates are available and were used as surrogates for the instantaneous data to be paired with the Ohio EPA data. A-2.2. Analysis For rural, unregulated streams in Ohio, it is recommended that the drainage area ratio method be applied only if the drainage area of the ungaged site is between 50 and 150 percent of the gaged site (Koltun and Whitehead 2002; Koltun 2003). Both stations have a drainage area of less than 50 percent of USGS gage 03238500 (White Oak Creek near Georgetown OH). Final Report A-4 TMDLs for the White Oak Creek Watershed The observed discharges at station 300057 ranged from 0.164 to 26.606 cubic feet per second (cfs) with an average of 5.714 cfs. The predicted discharges at station 300057, using the drainage area ratio method, ranged from 0.8 to 34.4 cfs with an average of 7.6 cfs. The percent error (observed minus expected, quantity divided by observed) ranged from -859 percent to 8 percent with an average error of -262 percent. The largest percent errors are for low-flow predictions. The data are displayed in Table A-2. Table A-2. Drainage area ratio method prediction for station 300057 Observed Estimated Station Gage Station Station Station discharge Gage discharge discharge % date time (cfs) date and time (cfs) (cfs) Error 4/10/06 1:30 PM 26.606 4/10/06 13:00 140 34.42 29% 5/18/06 10:20 AM 8.69 5/18/06 10:00 46 11.31 30% 7/18/06 2:42 PM 1.3884 7/18/06 15:00 12 2.95 113% 7/27/06 10:20 AM 0.497 7/27/06 10:00 10 2.46 395% 8/3/06 9:45 AM 0.415 8/3/06 10:00 6.9 1.70 309% 8/7/06 1:05 PM 0.1639 8/7/06 0:00 3.4 0.84 410% 8/31/06 9:00 AM 0.282 8/31/06 9:00 11 2.70 859% 9/8/06 11:11 AM 0.1795 9/8/06 0:00 3.3 0.81 352% 9/20/06 2:45 PM 1.273 9/20/06 15:00 12 2.95 132% 12/14/06 1:30 PM 17.647 12/10/06 14:00 66 16.23 -8% The observed discharges at station X02W06 ranged from 0.218 to 14.094 cfs with an average of 3.175