North Dakota StreamStats

North Dakota StreamStats incorporates statewide regression equations for estimating instantaneous peak flows with annual exceedance probabilities of 50, 20, 10, 4, 2, 1, and 0.2 percent. These peak flows have recurrence intervals of 2, 5, 10, 25, 50, 100, and 500 years, respectively. The report below documents the regression equations, the methods used to develop them and to measure the basin characteristics used in the equations, and the errors associated with estimates obtained from the equations. Users should familiarize themselves with this report before using StreamStats to obtain estimates of flows for ungaged sites in rural drainage basins.

• Williams-Sether, Tara, 2015, Regional regression equations to estimate peak-flow frequency at sites in North Dakota using data through 2009: U.S. Geological Survey Scientific Investigations Report 2015–5096, 12 p.

Regression equations for estimating streamflows that are exceeded 90, 75, 50, 25, and 10 percent of the time, the 1-, 7-, and 30-day seasonal mean high flows for the 10-, 25-, and 50-year recurrence intervals; and the 1-, 7-, and 30-day seasonal mean low flows for the 2-, 5-, and 10-year recurrence intervals have been published in the report below but they are not yet available in StreamStats:

• Williams-Sether, Tara, and Gross, T.A., 2016, Regression equations to estimate seasonal flow duration, n-day high-flow frequency, and n-day low-flow frequency at sites in North Dakota using data through water year 2009: U.S. Geological Survey Scientific Investigations Report 2015–5184, 12 p.

Click on this link to obtain general information on the North Dakota application, as well as specific sources and computation methods for basin characteristics.
 

Notice for delineations in small basins within Regions B and C:

North Dakota peak-flow regression equations for Regions B and C include Ruggedness Number as an explanatory variable. One of the basin characteristics needed to compute Ruggedness Number is the length of mapped streams within the delineated basin. Mapped streams are those streams found in the high-resolution National Hydrography Dataset flowlines layer, and displayed in StreamStats' default basemap layer. Especially in areas of poorly developed drainage, it is possible to delineate a basin within StreamStats that does not include any mapped streams. Presence of the blue stream grid raster does not always indicate the presence of mapped streams. Turning off the stream grid layer may make it easier to determine if a basin contains a mapped stream. In StreamStats Version 3, the stream grid layer can be turned off by unchecking the Stream Grid box in the left pane. In Version 4, the stream grid can be turned off by clicking on the layers button in the upper right corner of the map pane, then unchecking the box for the state map layers. When a delineated basin does not contain a mapped stream, the value of the Ruggedness Number will be zero, and consequently force peak-flow values of zero. In Regions B and C, StreamStats is only able to compute valid peak-flow values for basins that include at least some portion of a mapped stream. 
 

NOTE: The information provided by StreamStats for USGS streamgages in North Dakota have not yet been updated to include the streamflow statistics and basin characteristics from the above reports. The published values from those reports should be used for any engineering or regulatory purposes in preference to the values provided by StreamStats until StreamStats can be updated.