StreamStats in Maine
StreamStats for Maine can be used to estimate (1) instantaneous flood discharges with exceedance probabilities of 0.5, 0.2, 0.1, 0.04, 0.02, 0.01, 0.005, and 0.002 (equivalent to 1.25-, 1.5-, 2-, 5-, 10-, 25-, 50-, 100-, and 500-year recurrence intervals, respectively) for small and large streams; (2) monthly and annual mean flows, as well as flows at the 1-, 5-, 10-, 25-, 50-, 75-, 90-, 95-, and 95-percent exceedance probabilities, and (3) 7-day, 10-year low flows for ungaged, unregulated, rural streams throughout Maine. In addition, StreamStats can estimate (1) June median flows for Southern Maine; (2) August median flows for regions of Southern, East Coast, and Aroostook County, Maine; and bankfull discharge, width, depth, and area for streams in Central and Coastal Maine. The reports below present the regression equations used to estimate the flow statistics, describe the errors associated with the estimates, and describe the methods used to develop the equations and measure the basin characteristics used in the equations. Limitations of the methods are also described in the reports; for example, all of these equations are appropriate only for ungaged, unregulated, rural streams in Maine. Users should familiarize themselves with the reports below before using StreamStats to obtain estimates of streamflow statistics.
- Dudley, R.W., 2004, Estimating Monthly, Annual, and Low 7-Day, 10-Year Streamflows for Ungaged Rivers in Maine: U.S. Geological Survey Scientific Investigations Report 2004-5026, 22 p.
- Dudley, R.W., 2004, Hydraulic-Geometry Relations for Rivers in Coastal and Central Maine: U.S. Geological Survey Scientific Investigations Report 2004-5042, 30 p.
- Dudley, R.W., 2015, Regression equations for monthly and annual mean and selected percentile streamflows for ungaged rivers in Maine: U.S. Geological Survey Scientific Investigations Report 2015–5151, 35 p.
- Hodgkins, Glenn A., 1999, Estimating the Magnitude of Peak Flows for Streams in Maine for Selected Recurrence Interval: U.S. Geological Survey Water Resources Investigations Report 99-4008, 45 p.
- Lombard, P. J., Tasker, G. D., and Nielsen, M. G., 2003, August Median Streamflow on Ungaged Streams in Eastern Aroostook County, Maine: U.S. Geological Survey Water-Resources Investigations Report 03-4225, 20 p.
- Lombard, P. J., 2004, August Median Streamflow on Ungaged Streams in Eastern Coastal Maine: U.S. Geological Survey Scientific Investigations Report 2004-5157, 15 p.
- Lombard, P.J., 2010, June and August median streamflows estimated for ungaged streams in southern Maine: U.S. Geological Survey Scientific Investigations Report 2010–5179, 16 p.
- Lombard, P.J., and Hodgkins, G.A., 2015, Peak flow regression equations for small, ungaged streams in Maine - Comparing map-based to field-based variables: U.S. Geological Survey Scientific Investigations Report 2015–5049, 12 p.
Peak-Flow Frequency Estimates: Two sets of peak-flow regression equations are available for Maine; those from Hodgkins (1999), which apply to the entire State and appear in a table with a heading of “Peak Flow Statistics”, and those from Lombard and Hodgkins (2015), which were meant for use with small drainage basins, and appear in a table with a heading of “Peak Small Basin Flow Statistics.” The small basin peak-flow estimates from the Lombard and Hodgkins (2015) should be used in preference to those from Hodgkins (1999) when the drainage area for user-selected sites is less than or equal to 12 square miles.
June and August Median Flow Estimates: StreamStats often provides two estimates of the June and August median flows (JUND50 and AUGD50) for user-selected sites in some parts of Maine. One set of estimates, which are available state-wide, are determined by equations from Dudley (2015), and appear in tables with headings of “Statewide June Flow Statistics” and “Statewide August Flow Statistics.” The other estimates are determined by equations from Lombard, Tasker, and Nielsen (2003) for areas in Eastern Aroostook County (AUGD50 only), Lombard (2004) for areas in Eastern Coastal Maine (AUGD50 only), or Lombard (2010) for areas in southern Maine (JUND50 and AUGD50), and appear in a table with a heading of “Regional Median Flows Statistics.” In cases where two estimates are available, the estimates from the “Regional Median Flow Statistics” table should be the preferred estimates.
Uncertainty: StreamStats reports the uncertainty of the flow estimates for ungaged basins when basin characteristics for selected sites are within the ranges of the basin characteristics of the streamgages that were used to develop the regression equations. Errors for basins with basin characteristics that are beyond these bounds are unknown. The applicable ranges of the basin characteristics are provided in the StreamStats outputs and messages are provided when basin characteristics are outside of the applicable ranges. Particular caution should be used for very small basins, as drainage-area delineations can have large percent errors due to their small size, and estimates from regression equations for small basins typically involve large extrapolations beyond the data used to develop the equations. Delineations for very small basins should be checked in the field.
Percent Storage: The availability of data that was based on lidar in some parts of the state, additional data refinements, and the automated determination of basin characteristics that in some cases were previously determined manually have resulted in differences between basin characteristics and flow statistics provided by StreamStats and those that were published in some of the reports. In particular, an adjustment was needed to StreamStats computations of the percentage of storage, which is used as an explanatory variable in the peak-flow equations by Hodgkins (1999). Percent storage was computed originally from paper maps, whereas for StreamStats it is computed from the digital National Wetlands Inventory of the U.S. Fish and Wildlife Service. The adjustment was applied to remove exhibited bias between the values from Hodgkins (1999) and those from StreamStats. Prediction errors in peak-flow estimates provided by StreamStats for Maine are likely to be somewhat greater than the values provided in the StreamStats output reports as a result of added uncertainty in determining the percentage of storage.
StreamStats for Maine was developed in cooperation the Maine Department of Transportation.