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Frequently Asked Questions - Hydrologic Studies
This FAQ page replaces the Hydrology blog. The following is a summary of that blog plus new, relevant questions.
2. Hydrologic Methods/Information
2.1 Methods the Hydrologic Studies program uses
2.2 Drought flows and volumes
2.3 Wetland hydrology
2.4 Specific site information
2.6 Matching TR-20 to Michigan methodology
2.7 Evaporation data
2.8 Rational Method
2.9 Water Budget Guidance
2.10 Inconsistent Discharges
3. Hydraulic Information
3.1 FIS model data
4. GIS Information
4.1 CGI information
1. Waterfall Information
Several links to Michigan waterfalls are:
There is also a book titled "A Guide to 199 Michigan Waterfalls." You can find more by doing an Internet search for Michigan waterfalls.
Aerial photography for all of Michigan can be downloaded by county from https://www.michigan.gov/dtmb/services/maps. Internet applications like Google maps, Bing Maps, or Google Earth will let you view aerial photography without the need to download the files and use a GIS viewer.
2. Hydrologic Methods/Information
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. The regression program is at http://water.usgs.gov/software/nff.html and TR-55 is at https://www.nrcs.usda.gov/resources?title=&resource_type=1970. (Refer to question 2.6 also.) 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 and it can be downloaded at http://water.usgs.gov/software/peakfq.html.
Drought flows are computed by our unit. Steve Holden is the drought flow contact and you can reach him at 517-331-2642 or use our discharge request form.
You can find a description of wetland hydrology in the U.S. Army Corps of Engineer's Wetland Delineation Manual. A link to the manual and other wetland information is on EGLE's Wetlands Protection page.
Flows calculated by the Hydrologic Studies staff are available at https://www.egle.state.mi.us/flow/index.shtml.
- Direct link to low flow data: https://www.egle.state.mi.us/flow/lflowqry.asp
- Direct link to flood flow data: https://www.egle.state.mi.us/flow/hflowqry.asp
- A map of real-time USGS gage data for Michigan streams is at http://mi.water.usgs.gov/. All USGS gage data is available through http://nwis.waterdata.usgs.gov/nwis.
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.
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. The PDF version of this report can be downloaded from https://www.isws.illinois.edu/pubdoc/B/ISWSB-71.pdf. You can divide the rainfall by the duration for a specified frequency to convert depth of rainfall to an intensity.
There is a map (figure 2) on page 4 of our General Guidelines for Calculating a Water Budget report for May - October from an open water surface. The total evaporation may be obtained from it. Then the distribution (%) is given on page 3 of the same report. The map is from the reference on page 9. For more information, contact the Hydrologic Studies Unit at 517-284-5567. Also note that daily evaporation is available for many sites through the Michigan Automated Weather Network, https://mawn.geo.msu.edu/. The report gives the procedure to convert PET data to Evaporation data on page 3.
2.10 I have been using the Discharge Data Base and Drainage Area Ratio Method for determining flood discharges used in "Level Two" scour evaluations. I have just encountered Culver Creek in Bay County. The discharges provided for the Midland Road crossing (6.9 sq mi) are considerably larger than those given just downstream at N Union Rd (7.3 sq mi). I realize that the methods of analysis are approximate but what is up with this? Are the drainage basins normalized top to bottom somehow? Your thoughts and any suggestions would be greatly appreciated.
I reviewed the peak flow estimates on Culver Creek. I found a discrepancy in the time of concentration estimates for Midland Road and North Union Road 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. I apologize for the oversight and thank you for bringing this to our attention. I've updated the peak discharges for Culver Creek. Please let me know if you have any additional questions.
3. Hydraulic Information
We scanned the hydraulic support data for FIS's several years ago, so we should at least have PDF copies of older HEC-2 runs for most of the state. These files have been made available at Flood Insurance Study supporting data) We only have the electronic files for the more recent studies. If you want something in particular, please contact us. (Contact Matthew Occhipinti)
4. GIS Information
We use the CGI landuse files because they are still our best available information. We will use more up-to-date shapefiles if someone sends it to us, but that situation is rare. More current data are usually tabulated on a countywide scale, and that information should be sent to CGI to include on the web site.
5. Streams, Lakes, and Ponds
For inland lake grant information, I would start with the Inland Lakes Program in EGLE's Water Resources Division. You can contact program staff at 517-243-6421.
Depth maps for many lakes are at https://www.michigan.gov/dnr/things-to-do/fishing/where/inland-lake-maps-a. 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, "bathymetry" maps can also be found on selected lakes by doing a water body search on the Michigan Recreational Boating System (MRBIS). Click on the bathymetry icon to see a PDF map of the lake. The MRBIS web site can be found at https://www.mcgi.state.mi.us/MRBIS/.
5.3 I have a pond that has been around for many years. I recently purchased this property and discovered that the pond has filled in over the years, as ponds do. Are there any programs that would assist a homeowner in digging out the pond to its previous depth?
That program is in EGLE's Remediation and Redevelopment Division. You can contact them at 517-284-5087.
5.5 I am looking for information on storm water responsibilities. The local drain commission modified the culvert in front of my house and now my house has flooded twice causing serious damages. The drain commissioner denies any responsibilities, and I need to get something done to fix the culvert properly and hopefully fix my property that was damaged and destroyed. Any information or advice would be greatly appreciated.