Klosterman, Wayne_ Q&ADecember 6, 2002
RE: Dubuque Stormwater Management Plan
Response to Letter from Mr. Klostermann Dated 21 November 2002
The following are HDR's responses to Mr. Klostermann's letter addressed to the Mayor.
Is there some plan to control the Windsor Street watershed other than conveying it to the
Bee Branch, as it does now? If not why not?
Response:
The Windsor watershed was studied as part of the Drainage Basin Master Plan.
Storm sewer improvements were recommended to improve an undersized storm
sewer on Windsor and Burden. The Windsor basin was studied to define regional
detention oppommities; however, because of the topography and land use of the
area, no suitable regional detention facilities were identified. Although some
open land exists it is located too high in the basin to provide useful storm water
detention.
2. Is it possible to core the 32nd Street cell deeper and not remove any homes ?
Response:
I am assuming you are referring to homes taken to.expand the 32nd Street basin.
We recommend increasing the basin size from the existing 46 acre-feet to 96 acre-
feet by excavation and by increasing the top of the berm that forms the cell.
We considered this approach, a deep excavation of the cell, in the early stages of
evaluating alternatives. Excavation beyond the depths recommended in the report
would require the installation of a pumping facility. To be effective, this storage
would have to continuously pump down to make sufficient storage volume
available for storm runoff. All low flow stormwater runoff from the 32nd Street
basin and infiltration from groundwater sources would have to be pumped from
the cell continuously. This would require a perpetual expenditure for energy and
may not be possible depending on the rate of ground water infiltration. Therefore
at this time we do not recommended excavating the 32nd Street cell deeper than
can be drained by a gravity flow system.
Many of the homes in this area have habitable floors below the elevation of the
existing top of the cell. We recommend purchase of these homes regardless of
other improvements as a matter of public safety. Other homes were shown to be
removed because the cost to providing safe assess, sewer and water exceed the
value of the structure.
3. Is there a possibility of wetland creation to the north of the Shooting Society Park?
Response:
The Shooting Society Park is located outside the limits of our study area and was
not considered in the development of drainage alternatives.
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Have you explored the possibility of conveying water from the 32nd Street Cell to the
north to the Flexsteel cell, enlarging the cell, and then pumping it to the north, instead of
placing it in the Bee Branch ?
Response:
As part of our study, we looked at the diversion of 100% of the flow from the 32nd
Street cell to the area north of Flexsteel. This alternative was rejected because it
consists of a trans-basin diversion, which we believe would be very difficult to get
permitted without extensive environmental studies and extensive mitigation
measures in the Maquoketa basin. If constructed, the City of Dubuque could
become liable for all future flooding damages in the Maquoketa basin.
Our recommendation is that runoff from the 32nd Street basin be reduced as much
as possible and future design efforts should focus on achieving that result. The
improvements recommended are very effective in reducing downstream flooding.
However, this basin is only 27% of the total Bee Branch drainage area. Beyond
our recommendations, a 100% elimination of runoff from this basin will help but
will not substantially reduce flooding below 24th Street where the runoff from
Kaufmann, Locust and Windsor Subareas converge.
Do you plan on field verifying your high water data with citizens that live in the identified
flood area ?
Response:
Yes, as a part of the alignment identification process, we recommend a
comprehensive data collection activity in which information about historic
flooding is collected. In addition ~o high water marks information on the nature,
frequency and duration of flooding, and photographs of past flood events would
all be very helpful.
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