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Maryland and District of Columbia StreamStats

Streamstats for Maryland was developed in cooperation with the Maryland Department of the Environment.

StreamStats has been implemented for the entire State of Maryland, with limitations. The reports below summarize the regression equations for estimating peak- and low-flow frequency statistics that are available for use in this application, and the availability of water-use information for some parts of Maryland:

None of the above reports specifically states that the regression equations are applicable to areas within the District of Columbia. However, StreamStats will use the Maryland equations to provide flow estimates within the District of Columbia, as hydrologic conditions there are considered similar to those in surrounding areas of Maryland. Users should familiarize themselves with each of the above reports before using StreamStats to obtain estimates of streamflow statistics for ungaged sites.

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


Low-flow frequency estimates are available from regression equations only for Eastern Piedmont subregions A through D, as defined by Carpenter and Hayes (1996). The extents of the low-flow regions can be displayed on the StreamStats map by selecting the check box to the left of the LowFlow Regions layer listed in the Map Contents panel. Eastern Piedmont subregions A through D are shown in Low Flow Regions layer as region 604 through 607. Regression equations were not defined by for the Southern region, shown as region 363 in the Low Flow Regions layer. Carpenter and Hayes (1996) provide guidance for estimating low flows in that region. Ries and others (2010) provide revised guidance for estimating low flows in a small area in the northeastern part of the region (near Bel Air), called the Bynum Anomaly by Carpenter and Hayes (1996). Regression equations for the Eastern Shore and Western regions, regions 603 and 608 in the Low Flow Regions layer, were not implemented because the manually computed basin characteristics used in the equations by Carpenter and Hayes (1996) could not be reliably duplicated from comparable digital datasets.

Water-use information currently is provided only for sites in Cecil, Harford, Baltimore County, Baltimore City, Howard, Anne Arundel, Montgomery, and Prince George's Counties. All users can obtain summaries of monthly and annual total withdrawals and returns for delineated basins in these counties; however, if part of a delineated basin is outside one of these counties, then it is possible that the water-use summary does not reflect all withdrawals and returns that may affect the stream. Site-specific water-use information is not available to the general public for security reasons. After clicking on the above Interactive Map link, a new window will appear that allows users to enter a user name and a password to gain access to the secure information. Users who do not need access to the secure information can click on the button labeled Enter StreamStats Application without a login to gain access to the non-secure functionality. Also in this window is information on how to request a login ID and password from the Maryland Department of the Environment, which manages access to the secure information. Work is underway to provide water-use information state wide.


Maryland Biological Stream Survey Data-Collection Sites can be displayed on the user interface by checking the box to the left of the layer labeled as Bio_Sampling in the Map Contents panel. Information for the sites can be obtained either by clicking on the Identify tool button and then on a site location, or by use of the stream-network navigation tools, as explained in the User Instructions. Information provided by the Identify tool appears in a tabular format, and includes the URL for the site in the on-line MBSS database that is operated by the Maryland Department of Natural Resources (MDNR). Definitions of the attributes presented for the sites and descriptions of data-collection methods are provided in a report by the MDNR, which can be accessed at the link below.

Use of the network-navigation tools allows the discovery of all MBSS sites upstream or downstream from a user-selected point. Users will receive a table of the discovered sites, with links to the on-line database pages for each site. Note that the network navigation capability was provided by use of a blind snap of the latitudes and longitudes for the sites from the MBSS database to the National Hydrography Dataset (NHD) stream network. As the snapped locations have not been quality assured, it is possible that some MBSS sites are located incorrectly on the stream network.

Before one of the network tracing tools (Ad Hoc Trace or Trace from Outlet) can be used to discover the MBSS sites, the Configure Network Trace tool must be used to set up how the tracing will be done. After clicking on the button for the tool, in the scroll-down list labeled Network, change the selected network from NHDPlus_NET to HYDRO_NET, which is the high-resolution NHD (1:24,000 scale). In the Trace scroll-down list, choose whether to trace upstream or downstream, and then select the layers to participate in the trace from the list below. The Bio_Sampling layer must be selected to participate in the trace if information on the MBSS sites is desired.