METNWS-01-14-21 WATER SURVEY FOR FLOOD RISK_PHOTO

A map shows the southern Illinois rivers and streams being surveyed by the Illinois State Water Survey to evaluate their flooding conditions. The area covers Massac, Johnson, Pope and Pulaski counties.

Survey teams are using the next few months to conduct flood studies of Massac Creek, primarily focusing within the creeks’ riparian corridor from the confluence with the Ohio River near Metropolis up to Rosebud Road. Residents should be aware of the periodic presence of survey crews in the area.

Data collection, the first phase of the project, begins this month and will end in the spring as stream conditions and weather allow.

The Illinois State Water Survey (ISWS) is working collaboratively on the project with the Illinois Department of Natural Resources-Office of Water Resources (IDNR-OWR) and the Federal Emergency Management Agency (FEMA).

The survey will measure the geometric features of Massac Creek, including the size and shape of bridges and culverts, using standard land surveying equipment and techniques. The information will be used to estimate water flow characteristics, like the depth and velocity of water, during certain flooding conditions.

“The Illinois State Water Survey regularly partners with the Illinois Department of Natural Resources to perform field surveys of rivers and streams. Field surveying is standard procedure for detailed analysis of rivers and streams,” explained Aaron B. Thomas, PE, CFM.

Thomas is a project water resources engineer with the ISWS at University of Illinois at Urbana-Champaign. ISWS has been involved in producing Illinois’ Flood Insurance Rate Maps since 2004. Studies are ongoing around the state every year. Recent ISWS studies include locations in the Little Wabash River watershed, Wabash River watershed and the counties of Macoupin, Bond, Pulaski, Alexander, Johnson and Pope.

“These studies are used to produce Flood Insurance Rate Maps (FIRM), which are intended to help Illinois residents and businesses understand their flooding risk, and are also used to guide agricultural and land development decisions, facilitate mitigation actions to avoid future flood losses and plan for future disasters,” Thomas said.

Surveying Massac Creek entails setting up survey instruments to obtain cross sections along the stream channel at specified intervals. Each cross section obtained captures the existing ground elevations in the channel, perpendicular to the stream. If water elevation is deep within the channel, a boat may be required to allow the surveyors to hold a rod so that the channel bottom elevation can be recorded. Structures, such as bridges and culverts, are also surveyed for opening size and overtopping elevations. Land survey instruments, including measuring tapes, rods and levels, are common tools used to collect the measurements.

“Surveyors will utilize public access and right-of-way whenever possible to access stream locations; however, some stream locations may require access through private property. We will work with individual property owners as needed to accommodate their needs and concerns. This work will not disturb or damage properties,” Thomas said.

Other flood studies within Massac County are also underway which do not require field survey information.

“ISWS could use photographs and information about past flood events to verify and validate study results,” Thomas said. “Residents with this type of information can provide it to ISWS to improve the results of the study.”

Photos, information or questions can be directed to Thomas at abthomas@illinois.edu or 217-333-7832.

Along with the data collection and modeling, ISWS will coordinate with community officials to show draft results of the study. A future phase of the project is updating the FEMA Flood Insurance Rate Maps for all of Massac County to include the current ISWS studies.

Additional information about flood studies and resources in Illinois is available at illinoisfloodmaps.org.

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