7.0 FORMULATION OF A RECOMMENDED PLAN
The recommended plan was chosen after a comparison of cost, feasibility, local acceptance, and benefits of the various options. Based on the detailed evaluation of the eleven alternatives and their variants presented in the previous chapter, Alternative 1 Option N (30-foot shelf from downstream of Tobin Ditch upstream to CR 400S) and Alternative 10 (update and enforce ordinances) are recommended. This recommended plan does not entirely meet the criteria developed in Chapter 3. However, because cost is a limiting factor, a recommended plan was chosen that maximized benefit for the expected available funding. If additional funding becomes available, the alternatives should be reevaluated. For example, Alternative 1 Option G (200-foot channel improvement thru town and 130-foot channel improvement from CR 200W upstream to Prairie Creek) would provide 100-year protection through the City of Tipton and 5- to 10-year protection in the agricultural reaches. Estimated costs for this option were $17.4 million. Another example is Alternative 1 Option L (60-foot shelf channel improvement from downstream of Tobin Ditch upstream to CR 400S) which is a more extensive version of the recommended plan. For the $4.9 million required to construct the latter alternative, the time that flood waters are out of bank in the agricultural reaches could be reduced to about 24 hours for the 2-year flood, about half the time of that achieved with the recommended plan. Based on current expected funding availability and the analysis of the options presented in Chapter 6, Alternative 1 Option N (30-foot shelf from downstream of Tobin Ditch upstream to CR 400S) and Alternative 10 (update and enforce ordinances) are selected as the Recommended Plan. Exhibit 2, Exhibit 3, and Exhibit 4 show the approximate 2-, 10-, and 100-year floodplains, respectively, for the recommended plan compared to the existing-condition floodplains. Exhibit 5, Exhibit 6, and Exhibit 7 provide the same information but with more detail for the flooded areas in town. Details regarding each recommended plan component are provided below. 7.1 RECOMMENDED PLAN COMPONENT 1 – EXTEND HYDRAULIC MODEL DOWNSTREAM TO MORSE RESERVOIR This plan component would allow the evaluation of impacts to downstream properties if the recommended plan is constructed. The additional modeling would include a total of about 10 miles, approximately 5 miles in Tipton County for which additional topographic mapping or survey data would need to be obtained and approximately 5 miles in Hamilton County for which the Hamilton County GIS data could be used. Existing FIS modeling for the remaining reach downstream to the reservoir could be used to complete the model for the entire reach. Data for approximately 8 bridge openings would also have to be obtained. It is recommended that although only the 2-, 10-, and 100-year floods would need to be modeled to determine any negative impacts, the 500-year flood and floodway calculations should be included. The addition of these two items is minimal in terms of cost but has the benefit of providing more complete modeling to IDNR for inclusion in the future Countywide updated FIS. This information would then be readily available for floodplain management and regulatory purposes. The estimated cost of this recommended plan component is about $60,000. 7.2 RECOMMENDED PLAN COMPONENT 2 – 30-FOOT SHELF CHANNEL IMPROVEMENT FROM ABOUT 2800’ DOWNSTREAM OF TOBIN DITCH UPSTREAM TO CR 400 SOUTH This plan component, previously identified as Alternative 1 Option N, would consist of a channel improvement along the entire reach from about 2,800 feet downstream of Tobin Ditch upstream to CR 400 South that consists of a 3-foot’ shelf at an elevation 3 feet above the existing channel invert. The shelf would have a 1% slope towards the ditch and would slope at 2:1 back up to existing grade. A typical cross section with and without the proposed channel improvement is shown below in Figure 25. The channel improvement would extend from about 2,800 feet downstream of Tobin Ditch up to County Road 400 South. The estimated construction cost of this component is about $1.9 million. Adding land acquisition costs brings the estimated cost to about $2.7 million.
Figure 25: Typical proposed and existing condition cross section This component would accomplish a portion of the objectives by eliminating flood damages below the 10-year frequency flood in the town of Tipton and reducing the time that crops would be flooded by the 2-year flood to less than two days and about two and a half days for the 10-year flood. A comparison of the 10-year frequency flood profile with and without Alternative 1, Option N is shown below in Figure 26. Existing conditions are shown in the solid line. The proposed condition is shown by the dashed line.
Figure 26: Comparison of 10-year Frequency Profile With and Without Recommended Plan A comparison to the 2-year frequency flood profile with and without Alternative 1, Option N is shown below in Figure 27. Existing conditions are shown in the solid line. The proposed condition is shown by the dashed line.
Figure 27: Comparison of 2-year Frequency Profile With and Without Recommended Plan This project would produce about 195,000 cubic yards of excavated soil that will need to be disposed of or stockpiled. Location of the stockpile will impact construction cost due to haul distances. 7.3 RECOMMENDED PLAN COMPONENT 3 – PROVIDE A COPY OF STUDY RESULTS TO LOCAL PLANNING OFFICIALS AND SUBMIT TO IDNR FOR INCLUSION IN FUTURE COUNTYWIDE FIS This component would provide a copy of the floodplain mapping and expected water surface elevations developed during this study to local planning officials for use as best available data to assist them in guiding future development away from areas of flood risks. The analysis would also be submitted to IDNR to be incorporated into the upcoming Countywide FIS mapping initiative. 7.4 RECOMMENDED PLAN COMPONENT 4 – MINIMIZE THE IMPACTS ON FLOODPLAINS THROUGH STRICT ENFORCEMENT OF STORMWATER AND FLOODPLAIN ORDINANCES This plan component, previously identified as Alternative 10, would require strict enforcement of updated stormwater (especially, requiring on-site detention without exceptions) and updated floodplain (requiring compensatory floodplain storage and appropriate flood protection grade elevations) ordinances within the Big Cicero Creek watershed. Bridge construction/replacement should also be required to be designed such that the 100-year and more frequent flood elevations are not increased. This component would accomplish the objective of reducing additional flooding problems due to future development. This component is especially important in the vicinity of Buck Creek. If present storage and flow capacity is not maintained or runoff volumes are increased, flooding along Buck Creek will be due to the Buck Creek watershed itself and not backwater from Big Cicero Creek. The benefit derived from the recommended plan will be lost in the Buck Creek vicinity if this happens. The estimated cost of developing new ordinances is approximately $10,000. 7.5 RECOMMENDED PLAN COMPONENT 5 – MAINTAIN THE CURRENT USGS STREAM GAGE ON BIG CICERO CREEK AND ADD ADDITIONAL GAGES AT KEY LOCATIONS IN THE WATERSHED Plan Component 5 would have the Drainage Board, County, and/or City of Tipton coordinate with the USGS to ensure the existing stream gage located near Arcadia is maintained and that additional gages be added in the watershed. Based on a review of the watershed, it is recommended that additional stream gages be installed at Ash or Main Street in Tipton and at the CR 500 West crossings of Big Cicero Creek and Prairie Creek. These stream gages would provide ongoing data regarding stream flow that can be used in the future to update hydrologic analyses of the watershed and to evaluate impacts of various projects in the watershed. The cost to the local entity for each gage would be approximately $10,000 for the initial installation and an additional $5,000 per year for maintenance. The total cost of this component would be approximately $30,000 with ongoing annual maintenance costs of about $15,000.
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