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- Click here for GISHydroNXT and GISHydro2000 on a Private Virtual Computer Lab (PVCL) at the University of Maryland. An account is required to log in. Click here for instructions on setting up an account.
- As of April 2023, off-campus users must connect to a Virtual Private Network (VPN) before the PVCL will become available. The following article gives an explanation and procedures: VPN Access from Off Campus
- Updated Version of the Office of Structures (OOS) Structure Hydrology and Hydraulics Division (SHHD) "Manual for Hydrologic and Hydraulic Design" (June 2020)
- New 2022 Regression Equations for the Eastern and Western Coastal Plain Regions. New Fixed Region regression equations (FRRE) were developed in 2022 for the Eastern and Western Coastal Plain Regions using updated SSURGO soils data. Click here for a brief discussion of the changes and why they were made. Updated versions of the Hydrology Panel Report appendices that document these equations are posted on this website.
Updated February 2024
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GISHydroNXT is a GIS-based software
program for performing hydrologic analysis. It
consists of a database of hydrologic layers and customized modeling tools in an ESRI ArcMap™
environment. Some Features Include:
- Complete database of DEM, Land use, and soils data for
Maryland drainage areas.
Watershed and channel delineation. Watershed statistics (drainage area, RCN, tc, more). Peak discharge estimates from USGS regional regression
equations (with confidence intervals). Interface to WinTR-20 for subdivision, parameter calculation,
rating tables, and channel routing.
Application of Hydrologic Methods in Maryland, a report prepared by the Hydrology Panel convened by the Maryland State Highway Administration and the Maryland Department of the Environment is available on the Hydrology Panel page.
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| New 2022 Regression Equations for the Eastern and Western Coastal Plain Regions
New Fixed Region regression equations were developed in 2022 for the Eastern and Western Coastal Plain Regions using updated SSURGO soils data. An Appendix 3 Update is posted on this website to document the 2022 regression equations for the Eastern and Western Coastal Plain Regions as an interim measure until the Sixth Edition of the Maryland Hydrology Panel report is published later in 2022. The 2022 regression equations are now the default regression equations in GISHydroNXT and GISHydroWEB. A brief summary of why new equations were developed follows.
The regression equations for the Eastern and Western Coastal Plains that are documented in the July 2020 Fifth Edition of the Maryland Hydrology Panel report were based on the May 2018 SSURGO soil database, which used the Dominant Component approach for aggregating the hydrologic soils data. The explanatory variable in the 2020 regression equations that represents soil conditions is the percent of Hydrologic Soil Group A (highest infiltration soils). On August 4, 2020, extreme flooding from heavy rainfall from Tropical Storm Isaias washed out the roadway approaches and damaged the bridge on MD 6 over Persimmon Creek in St. Mary’s County in the Western Coastal Plain Region. The Maryland Department of Transportation State Highway Administration (MDOTSHA) performed hydrologic analyses on Persimmon Creek as part of designing a new bridge for MD 6. During this analysis, it was determined that there was a significant difference in the percent A and B soils based on the 2018 SSURGO soils data in GISHydroNXT (based on Dominant Component) and the current (2020) default data in the NRCS Soil Survey web site (based on Dominant Condition). Apparently between 2018 and 2020, NRCS changed the default option for aggregating the soils data on the Soil Survey web site. As a result of the MD 6 analyses, it was determined in the TR-20 analysis that the Dominant Condition soils data provided more reasonable T-year flood discharges. New SSURGO soils data were downloaded in October 2021 and used to develop new Fixed Region regression equations for the Eastern and Western Coastal Plain Regions using percent A soils based on the Dominant Condition. The new regression equations were significantly more accurate for the Western Coastal Plain Region, particularly in St. Mary’s County and about the same for the Eastern Coastal Plain Region, compared to the 2020 equations. The 2022 regression equations for the Eastern and Western Coastal Plain Regions are summarized in the Appendix 3 Update posted on this website.
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