GREEN CONSTRUCTION

Low-water mark MoDOT makes a difference with mitigation projects

t’s inevitable. No matter how hard de- weekends. With many access points and traf- fi c signals along the existing route, the high partments of transportation try to avoid volume of motorists often made it diffi cult for I it, construction projects have an impact traffi c to fl ow effi ciently through the area. The scope of the expressway project re- on their surrounding environment. quired MoDOT to mitigate, or compensate, for the environmental impacts it would have on The impact becomes even more pro- the area. Mitigation can take place in a variety nounced when a project is in an area renowned of forms. However, since mitigation banks are for its lakes, rivers and streams. the preferred option of the U.S. Army Corps of Such was the case when the Missouri Engineers, MoDOT selected multiple low-water Department of Transportation (MoDOT) crossings located in the same stream reach and was preparing for construction of a four-lane collectively proposed them as a “bank.” expressway in the Lake of the Ozarks area of Forming its fi rst stream mitigation bank Camden County in 2007. The 54,000-acre would be just as challenging for MoDOT as it lake and surrounding state park is a popular would be benefi cial. It would require multi- tourism attraction because of its abundance of agency approval, but it also would optimize aquatic activities, from boating and water ski- the ecological benefi ts of removing multiple ing to fi shing and swimming. barriers from a large stream reach and gener- Construction of the new expressway had ate a greater amount of credits that could become necessary to improve safety and relieve be banked for immediate and future stream congestion through the lake area as travel vol- mitigation needs. umes on the existing Rte. 54 were ranging from As a result, the department was able to 43,000 in off-peak times to over 50,000 during couple the use of its greatest asset, engineer- peak periods, such as holidays and summer ing, with natural design concepts to produce

44 February 2011 • ROADS&BRIDGES an excellent mitigation project and save Missouri departments of Conservation agreement was signed, it allowed the taxpayer dollars in the process. and Natural Resources and U.S. Fish department to temporarily take that and Wildlife Service-Region 3 to gain crossing into the state’s system; design, Opening a bank approval for the survey methodology bid and construct the project; and then Prior to these projects, MoDOT had that now determines the amount of transfer it back to the county once con- found it diffi cult to develop a stream compensation that can be received for struction was complete. mitigation bank because of the amount low-water crossing improvements. “These low-water crossings were on of land acquisition required to generate In the end, MoDOT’s fi rst stream miti- county roads, but the economic and bank credits. gation bank was approved by the regula- environmental benefi t made them ideal Fortunately for MoDOT, the Missouri tory and resource agencies. With the for MoDOT to help meet our federal re- Department of Conservation had voiced methodology now in place, the process quirements for our construction projects a need to address the low-water cross- required for future mitigation using low- in Camden County,” said Nicole Hood, ings within the habitat of the federally water crossings will be much simpler and MoDOT project manager. “Our standard threatened Niangua Darter, because they will result in more timely reviews and mitigation efforts for general construction were believed to be one of the reasons approvals by the U.S. Corps of Engineers projects usually include planting trees the fi sh population was declining. Be- when using this type of mitigation. By or stabilizing nearby stream banks. The cause this species is considered threat- consolidating efforts for stream mitiga- amount of stream mitigation needed for ened, improving its habitat to provide tion into one bank proposal, future miti- multiple construction projects forced us long-lasting stream benefi ts was a prior- gation needs will be met until all bank to look at a large-scale mitigation project. ity. All four of the low-water crossings credits have been used. Another benefi t This project has allowed us to make sev- selected for modifi cation were along the of the stream mitigation bank is that it eral improvements to the transportation Little Niangua River in Camden County, eliminates the need to commit other system and provide great benefi ts to the one of the streams in which the Niangua MoDOT resources (such as survey, right- area’s natural habitat and wildlife.” Darter resides. of-way, design, etc.) as would be required To date, the department has com- Although the location of these proj- for individual mitigation projects. pleted modifi cations to four low-water ects proved ideal for a stream mitigation crossings, all on county roads over the bank, there was still another hurdle to Crossing county lines Little Niangua River in Camden County. cross. Up to this point, there was no With the process approved, MoDOT Those include Griswald’s Slab on Coun- accepted methodology to calculate the was ready to go to work on the mitiga- ty Road N-145, Green’s Slab on County amount of stream mitigation credit tion projects. However, the crossings were Road N-166R, Howard’s Ford on County received by modifying or replacing low- located on county roads, so MoDOT had Road NN-166 and Bannister Ford Cross- water crossings. to secure an agreement with Camden ing on County Road N-165. Before any of these low-water County to work on each crossing. Prior All of the low-water crossings were modifi cation projects could begin, to every project, MoDOT sought input modifi ed using precast concrete beam MoDOT had to collaborate with all from county commissioners and engi- spans to enable the natural stream bot- fi ve Missouri Corps districts, Region 7 neers regarding alignment, width of the tom to adjust with fl ow events and allow Environmental Protection Agency, the bridge and safety improvements. Once an more natural sediment to fl ow through

To date, the department has completed modifi cations to four low-water crossings, all on county roads over the Little Niangua River in Camden County. Those include Griswald’s Slab on County Road N-145, Green’s Slab on County Road N-166R, Howard’s Ford on County Road NN-166 and Bannister Ford Crossing on County Road N-165.

ROADSBRIDGES.com 45 Construction of Griswald’s Slab and Howard’s Ford included the removal of the 60-ft opening at each of the existing crossings where low water was fl owing most of the time. The old concrete was replaced with two new 30-ft concrete slabs. Griswald’s Slab was raised 1 ft, but Howard’s Ford remained at the same elevation. MoDOT recycled the concrete pavement it removed from each crossing. the structure. Each of the new crossings new Rte. 54 Expressway was opened to time to locate, secure and design project- was made 3 ft wider than the exist- traffi c. The next 4-mile stretch of the specifi c stream mitigation for future ing ones to a width of 17 ft, with the $48.7 million project is scheduled to projects, because the credits are already exception of the Bannister Ford Cross- open in late 2011. available for use. ing. At the request of Camden County, While the expressway, once fully For motorists, these improvements it was widened from 14 ft to 15 ft 4 in., completed, will improve safety and have helped increase safety. The design with 10-in. curbs on each side. Practical traffi c fl ow for residents and tourists, the of the new structures has decreased design was applied, allowing MoDOT to low-water crossings are producing their the frequency and duration of fl ood- keep the existing roadway alignment on own multiple benefi ts now and for years ing, making it easier and safer for local each project. to come. From an environmental stand- residents, mail carriers and school buses Construction of Griswald’s Slab and point, the new crossings provide a great to use them. Howard’s Ford included the removal of benefi t to area wildlife. The new, higher Finally, the new structures MoDOT the 60-ft opening at each of the existing crossings have improved water fl ow and built have resulted in reduced main- crossings where low water was fl owing increased fi sh migration, especially for tenance needs and expenses for most of the time. The old concrete was the Niangua Darter. Camden County. replaced with two new 30-ft concrete “Low-water crossings on Missouri Overall, the low-water crossing proj- slabs. Griswald’s Slab was raised 1 ft, but county roads can limit aquatic organism ects have been a resounding success, and Howard’s Ford remained at the same movement because they create barriers not just in MoDOT’s opinion. The effort elevation. MoDOT recycled the concrete for fi sh and other aquatic organisms has been rewarded at both the state and pavement it removed from each cross- moving upstream and downstream,” said national level, receiving the 2009 Practi- ing, broke it up and reused it as stream- Melissa Scheperle, MoDOT senior envi- cal Design Awards for Excellence from bank protection. ronmental specialist. “By modifying these the Transportation Engineers Association Both Bannister Ford crossing and structures, populations are reconnecting, of Missouri and the prestigious 2009 En- Green’s Slab were completely replaced, which increases opportunity for genetic vironmental Excellence Award from the leaving none of the previous structure. diversity and boosts population growth.” Federal Highway Administration. Green’s Slab involved the replacement But the benefi ts do not stop there. Looking ahead, MoDOT will care- of the 60-ft crossing, with two new 30-ft Because low-water crossing improve- fully weigh the economic and environ- 1 slabs 2 ⁄2 ft higher than the original ments provide greater benefi ts to stream mental benefi ts that additional low-wa- structure. Bannister Ford required two habitat than other smaller projects, they ter crossings may provide as mitigation 45-ft slabs to replace the 90-ft crossing. generate a greater amount of stream on future projects. The new structure was elevated a ½ ft compensation, allowing MoDOT to For more information about Mis- higher than the one it replaced. have credits available for future projects. souri’s low-water crossings improve- So far, this process has saved Missouri ments, go to www.modot.org/ehp/ Credit is due taxpayers nearly $3 million. StreamMitigation.htm. R&B The last low-water crossing modifi ca- The process also will help deliver tion was completed in September 2009. some future projects faster, because the Information for this article provided by the Missouri One year later, a 5-mile section of the department no longer has to take the Department of Transportation.

46 February 2011 • ROADS&BRIDGES