Some thoughts on Lower Gar
To the Editor:
In 1997, the Army Corps of Engineers conducted a $250,000 study for the Iowa DNR and Dickinson County. Their report stated at page 58:
"With the addition of the emergency culverts in 1993, the flooding threat to Spirit Lake was greatly reduced. However, the Okoboji chain still faces much the same flood threats it did before the emergency culvert was put in place [on Lower Gar in 1993]."
The Corps went on to state that a bridge across the 230th Avenue causeway provided the most flood protection for the Okoboji chain of lakes. The Corps also suggested adding additional box culverts to provide more outlet capacity.
The Dickinson County Supervisors have rejected the Corps' suggestions and have adopted a plan and let bids for a design proposed by a member of the public who is not an engineer. That plan calls for 2 elevated box culverts, installed with their bases 6" above the downstream Iowa DNR dam/weir. The elevation of the culverts diminishes the outlet and flood protection. The bid accepted is for $357,000. $100,000 of that cost is for the sheet piling and concrete to carry out the layman's idea of elevating the culverts, rather than resting them on lake bottom. The Iowa Department of Transportation (IDOT) had initially pledged $100,000 toward the project to increase the outlet through the roadway. According to a June 2, 2010, KUOO report, the IDOT has withdrawn that pledge because the design chosen by the Supervisors is not one proposed by the Corps. The same report states that because of the change, an additional study by the Corps is required at a cost of $9,850. Because the Supervisors deviated from the Corps' suggestions, it will cost county taxpayers $209,850 in additional expense and a lost contribution from the IDOT.
What will taxpayers get for this additional expense? On Sept. 1, 2010, the Iowa DNR issued the permit to construct the elevated culvert system, even though the Corps' $9,850 study had not been completed. Attached to the permit is a hydraulic analysis table of the increase in outlet from the elevated culverts structure. The table shows with a "100 year flood" the Okobojis lake level will exceed the weir crest by 3.66 feet. It also shows the "Proposed Conditions" of two elevated culverts only lowers the lake level during a 100 year flood by 0.03 ft., or 0.36 INCH. So, for the extra $209,850 the Okoboji chain gets a bit over a third of an inch flood reduction. There is no data regarding flood stage duration. Extended flood durations expose the Okoboji chain to wave damage, or more flooding from subsequent rainstorms. According to the contract between the county and the Corps, that duration information will be supplied by the Corps' pending study.
The 100 year flood standard used by the Iowa DNR has proved to be a dangerous and inadequate standard. The Iowa City/Cedar Rapids area had 500 year floods in 1993 and 2008. Ames had 500 year floods in 1993 and the Summer of 2010. It is yet to be determined if the flooding of southeastern Minnesota last September is classified as a 500 year flood.
In view of those recent "500 year flood" experiences, the DNR's use of a 100 year flood standard makes no sense. It provides little or no capacity for future urban growth and increased impervious surfaces. A 0.36 inch decrease in flood levels for $357,000 cost provides virtually no flood protection.
We do not have the report from the study the Corps is presently conducting, but their thoughts regarding the elevated structure may be indicated from the last paragraph of the contract the County signed with the Corps for the study:
The results of the analyses proposed herein do not and will not constitute endorsement of any alternative evaluated. It shall be the responsibility of the appropriate local governmental authorities to decide the appropriate course of action in regards to Lower Gar outlet modification. The results of previous and proposed study are intended to be guides to those decisions.
Unfortunately, the Supervisors have chosen to proceed with the project without waiting for the Corps' report.
Finally, the Iowa DNR is requiring Dickinson County to report to the Federal Emergency Management (FEMA) regarding the effects of the proposed project on the flood plains around the lakes. The County and many of the municipalities do not belong to the federal flood insurance program. However, this data will be included in the Flood Insurance Rate Maps (FIRMs), used by FEMA and commercial flood insurance companies to assess risk and set premiums. Recent banking regulations require flood insurance for newly mortgaged properties in flood plains, which may face higher premiums, or an inability obtain flood insurance, due to the inadequate outlet.
The numbers show that the flood threat the Corps warned about in its 1997 report is far from being alleviated and taxpayers' money is being wasted.