Public Information Newsletter Otonka Trail Phase II Drainage
Channel Improvements
Volume 6 October 16, 2013
Thank you to all of the residents who attended the September
26th Public Meeting. We had a great turnout with 22 property owners
represented. This newsletter is intended to address some of the
questions discussed at the meeting.
The City’s goal remains to assist the neighborhood with your
drainage concerns. Following a review of the original plat, the
easement rights for the drainage channel have been challenged. The
original covenants recognized this is a natural drainageway and
placed responsibility with the surrounding homeowners to keep the
drainageway free of trees and debris. Until this item is resolved,
final design will be suspended. The City hopes to avoid legal
action and wants to work with the property owners to secure written
permanent drainage easements required to carry the 100-year storm
event. Once the easement item is resolved, a permanent resolution
can be defined for this area.
A few residents were concerned about the storm drainage entering
the channel from City streets upstream. Aerial photos of this area
are attached to this newsletter to illustrate the long-standing
natural path of water through this area. The photos include aerials
from 1940, 1962, and 1975. Each photo shows the drainage channel in
the same location conveying water toward the Big Sioux River.
Nearly the entire drainage basin is covered with houses and streets
by 1975. The design of the subdivisions followed the same drainage
rules that apply today; preserving the natural path of water as
much as possible.
A tributary map showing the path of water in this neighborhood
is also attached for your reference. The streets and upstream
development have been in place since the 1970’s. The upstream
development was constructed very similar to your development. It is
entirely residential housing with little change to the natural
topography of the site.
Another attachment to this newsletter shows the elevations along
49th Street. The water passes through the low point at Otonka Pass.
There were suggestions voiced at the last public meeting that the
City evaluate redirecting the natural flow of the upstream water.
If the developer south of 49th Street were required to reroute the
stormwater away from this natural channel, they would have had to
overcome a significant elevation change. A question was posed at
the meeting about the possibility of routing flow down Otonka Trail
rather than through the natural channel. The drainage model shows
the total flow to be approximately 190 cubic feet per second for a
100-yr, or 1% chance, storm event. Capturing this amount of flow
and rerouting it in a pipe and within the curb and gutter, a
different direction than the natural flow path, would be a
significant effort. In large events, curb overtopping is likely,
which would cause additional front and side-yard flooding as the
water passes between homes into the natural channel.
The preliminary design presented at the meeting showed some
design aspects that will help reduce the velocity of the water in
the channel. Placing rock drop structures in the channel will help
create a flatter channel slope as well as reducing the water’s
energy as it flows through the rock. Resident input drove a
majority of the tree removal and protection throughout the full
project limits. If the project continues forward, the design will
continue to progress toward final design where many more details
are finalized, including type of rock, type of grass seed, channel
bottom design, etc.
We expect to have another public meeting in the near future to
further discuss your concerns and update you on the easement
discussions. We encourage you to contact us if you wish to have
another individual meeting to discuss the project further.
City of Sioux Falls HR Green, Inc. Andy Berg Dena Knutson Dawn
Horner Principal Engineer Project Manager Project Manager
605.367.8637 605.367.8630 605.221.2654 [email protected]
[email protected] Cell 605.351.2711 [email protected]
mailto:[email protected]:[email protected]:[email protected]
