Osceola Rural Water System
- Floodplain modeling
- Engineers set the well heights, designed flood protective measures to extend a safe distance above both the modeled flood level and known historic flood levels
- Employed a Geographic Information System (GIS) to determine the 100-year flood elevations and delineate the floodway boundaries
- Verified if the proposed wells were within the floodplain, then determined whether they were within the floodway or the flood fringe
- Secured permits for three new well sites
Constructing a project within a floodplain is sometimes unavoidable and can be successful with proper planning and foresight. DGR Engineering (DGR) helped Osceola County Rural Water System, Inc. (OCRWS) navigate many challenges to develop a wellfield in a floodplain. OCRWS was scrutinizing six potential shallow well sites in a floodplain based on the results of an exploratory study of the alluvium (sand and gravel). The natural presence of groundwater within said alluvium lends itself to the need for construction within the floodplain.
DGR employed a Geographic Information System (GIS) in conjunction with the U.S. Army Corps of Engineers’ HEC-RAS program to first determine the 100-year flood elevations and delineate the floodway boundaries. This step allowed engineers to verify if the proposed wells were within the floodplain, and then determine whether they were within the floodway or the flood fringe. The aerial map at top provides an illustration of the modeling results. Of the six sites, two were determined to be outside of the floodplain, two within the flood fringe, and two within the floodway. Moving forward with three of the four wells outside of the floodway, DGR engineers set the well heights and designed flood protective measures to extend a safe distance above both the modeled flood level and known historic flood levels.
It is imperative to a safe drinking water supply that the wells are not inundated by floodwaters and potential contamination. The Iowa Department of Natural Resources (local FPA) approved permits for the wells to be constructed. The story remains to be told on the two possible well sites in the floodway. In the end, DGR’s team was able to secure permits for three new well sites, providing a vital water source to OCRW and its customers.
FLOODWAY: The stream channel and that portion of the adjacent floodplain that must remain open to permit passage of the base flood with a designated surcharge, in the water surface elevation. Flood waters generally are deepest and swiftest in the floodway, and anything in this area is in the greatest danger during a flood. The floodway must remain free from obstruction so that the 100-year flood can move downstream.
FLOOD FRINGE: The remainder of the floodplain is called the flood fringe, where water may be shallower and slower. FEMA and state regulations allow the flood fringe to be obstructed if standards (i.e., elevating and flood proofing requirements) are met.
- Electrical Power
DGR Engineering (DGR) worked with the City and the project architect for all aspects of the project including topographic survey, site design, construction survey, construction observation and administration.
Sioux City, Iowa
Sanitary Sewer Rehabilitation
The project was bid and came in under budget. Manhole lids were raised to provide better access in some areas, and rehabilitation of the sewer system was completed to give another 50 years of life to the City’s much-needed infrastructure.
Wastewater Treatment Facility
MBBR technology was chosen based on cost, operational flexibility and most importantly, limited land availability.
DGR employed a Geographic Information System (GIS) in conjunction with the U.S. Army Corps of Engineers to first determine the 100-year flood elevations and delineate the floodway boundaries.
Due to concerns with the age and condition of the structures, along with safety clearances to energized equipment and conductors, a project was undertaken to replace the old infrastructure with new underground lines and associated padmount equipment.
Redwood Falls, MN
Street & Utility Improvements
Morningside Avenue was reconstructed totaling approximately 1,300 linear feet. The project included new sanitary sewer, water main, storm sewer, fiber conduits, decorative street lighting, and 9-inch concrete paving with colored concrete sidewalks.
Sioux City, IA