Paper
Stream Low Flows and Regulatory Low Flows Estimation for National Pollutant Discharge Elimination Systems (NPDES) Permitting in Changing Climate
- Authors:
- Suresh Sharma; Keshav Khanal; Taylor A Marucci
- Abstract
- The conventional point source discharge permitting decision through the National Pollutant Discharge Elimination System (NPDES) is primarily based on the regulatory low flows such as hydrological (7Q10, 1Q10), biological (4B3, 4B1) and seasonal low-flow conditions. These regulatory low flow conditions are often estimated based on long-term historical flow data and can be expected to meet regulatory water quality protection provided that long-term data are utilized. Since climate change has potential to change the future low flow in the stream, concerns arise regarding the benefit of using long-term data for regulatory low flow estimation. We conducted a study in the Ohio River Basin and some of the selected regions of the Mid-Atlantic and Great Lake to examine the relevance of long-term data for regulatory low estimation. First, we detected the climate change pattern, and then, the study was conducted at various hydro-climatic data network (HCDN) stations to analyze the sensitivity of estimated hydrological/biological conditions on the length of data records. We analyzed the long-term data records for regulatory low flow estimation using various spans of data records. Our analysis indicated that long-term data were not necessarily beneficial for regulatory low flow estimation. The 50th percentile area-normalized 7Q10 indicated that 50 to 60 years of data was sufficient to capture minimum low flows. The average normalized 7Q10 computed using more than 60 years of records started increasing. However, the mean and median 7Q10 computed separately for summer and winter tended to increase for the last 40 years and decreased for the data used beyond 40 years of record. In summary, data of more than 60 years duration in any period over the historical period may not be needed to capture the lowest flow in this climatic region as the lowest flow either increases or remains constant after this period. Our analysis suggests that the large period of records may not be beneficial for regulatory low flow estimation.
- Keywords
- NPDES Permitting; Low Flow; 7Q10; 1Q10; 4B3; 1B3; Hydrologic and Biologic Condition
- StartPage
- 432
- EndPage
- 449
- Doi
- 10.5963/JWRHE0404018