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FAQ: Hydrology

A peaceful and small waterfall in the Upper Peninsula
Environment, Great Lakes, and Energy

FAQ: Hydrology

Hydrology is the occurrence, distribution, and movement of water.  Current and projected flows of rivers and streams is a primary focus of the Hydrologic Studies Program of the Water Resources Division.

  • Several resources listing locations of Michigan waterfalls are:

    If you are close to Detroit, the Michigan Outdoor Adventure Center offers an interactive waterfall exhibit – walk behind and touch an indoor waterfall to get a glimpse of what it’s like to visit one of Michigan’s 150+ waterfalls!

    Many of our staff find the book titled "A Guide to 199 Michigan Waterfalls" useful when finding locations to visit.

  • Most search engines or mobile map apps offer aerial imagery for most locations, though many waterfalls are in remote locations and may not be easily visible on these platforms.

    If you need more detailed aerial imagery, such as for a GIS project, you can download aerial imagery for the whole state by county at – though you will need a GIS application to view the data.

  • We use our modified SCS method and NRCS' Windows TR-55 program for small watersheds and the USGS regression method for larger ones.  Our SCS method can be downloaded from our hydrologic studies web page. View the regression program and TR-55. If stream gage data are available, we will use a statistical frequency analysis of the annual maximum floods. We use USGS' PEAKFQ program for the statistical analysis.

  • Drought flows are computed by staff in our Hydrologic Studies and Floodplain Management Unit. Steve Holden is the drought flow contact and you can reach him at 517-331-2642 or use our discharge request form.

  • Wetland hydrology refers to the timing and extent of flooding or soil saturation and is considered to be the "driving force" in wetland formation. Rainfall, soil permeability, position in the landscape, surrounding land use, and type of vegetation all influence the hydrology of a wetland.

    This is a simplified answer; for a more thorough and technical explanation, please reference the U.S. Army Corps of Engineers Wetland Delineation Manual. You can also find additional information on wetlands on EGLE's Wetlands Protection page.

  • Topographic maps are most often used both to measure the main channel length and the percentage that passes through swamps and lakes.  If you use the paper maps, dividers are used to measure the respective lengths.  We do all of our measuring digitally using ArcGIS and its measuring tools.

  • You can use TR-20 (and Win TR-55) to reproduce the Michigan SCS results, but you need to input the Michigan-specific dimensionless unit hydrograph ordinates into each program.  The triangular version of these ordinates are: 0.0, 0.5, 1.0, 0.8, 0.6, 0.4, 0.2, and 0.0. 

  • NOAA Technical Report NWS 33 is an evaporation atlas for the U.S. This includes maps of evaporation from an open water body annually and seasonally.  The report and maps are from various sources online including DjVu Document (

  • EGLE does not use or recommend use of the rational method.  For very small watersheds, we use the NRCS Windows TR-55 method.  If you do use the rational method, it should be limited to the smallest of watersheds (<20 acres), preferably with one, single land use.  All of the methods we use are based on total rainfall, not intensity.  The rainfall values are in the NWS publication "Rainfall Frequency Atlas of the Midwest," Bulletin 71. You can divide the rainfall by the duration for a specified frequency to convert depth of rainfall to an intensity. 

  • Pan evaporation data can be found in our General Guidelines for Calculating a Water Budget report for May - October from an open water surface. There is a map (figure 2) on page 4 of the report for May - October from an open water surface.  Total evaporation may be obtained from it.  Then the distribution (%) is given on page 3 of the same report.  The map is from the MSU Agricultural Weather Office which also provides daily evaporation for many sites through Enviro-weather. The report also gives the procedure to convert Potential Evapotranspiration (PET) data to Evaporation data. For more information, contact Hydrologic Studies staff at 517-284-5567. 

  • Hydrologic Studies staff reviewed the peak flow estimates and found a discrepancy in the time of concentration estimates that doesn't seem justified, given the proximity of the two sites.  These issues are typically addressed when a new discharge is estimated and compared to those previously reported.  We apologize for the oversight and thank you for bringing this to our attention.  We've updated the peak discharges.  Please contact Hydrologic Studies staff if you have any additional questions or notice any other discrepancies. 

  • Supporting hydraulic model data for some older Flood Insurance Studies is maintained at the FEMA Engineering Library at Working with Flood Risk: Engineers, Surveyors or Architects. Contact Matthew Occhipinti, 616-204-1708, if you have additional questions.

  • We use the Center for Shared Solutions land use files because they are our best available information.  We can use more up-to-date shapefiles if provided, but that situation is rare.  More current data should be sent to CSS to include on the GIS Open Data Portal web site.

  • Depth maps for many inland lakes are available from the DNR. If the lake you want is not listed, you can contact EGLE's Inland Lakes Program at 517-243-6421 to see if they have other information. Lake depths or "bathymetry" maps and other information can also be found on the Michigan Recreational Boating System (MRBIS).

  • It depends – depending on the proposed location, adjacent water features, and size, a permit may be required from EGLE and/or your local unit of government. You should always check with your local authorities before beginning any construction on your property. There may be potential negative impacts to wetlands, lakes, streams, or other natural features that need to be considered and avoided or minimized as much as possible during construction. For more information, please review our Pond Construction PDF, contact your local Land/Water Permit staff, or contact EGLE's Environmental Assistance Center at 800-662-9278.

  • You should contact your local drain commissioner with any concerns regarding flooding on your property. If you are unable to resolve your issue locally, please contact your local district staff person listed on the Land/Water Permit staff map or contact EGLE's Environmental Assistance Center at 800-662-9278.