HomeMy WebLinkAboutCCMinutes_2006_03_07 79
Brookings City Council
March 7, 2006
The Brookings City Council held a special meeting on Tuesday,March 7 at 4:00 p.m. at City Hall
with the following members present: Mayor Scott Munsterman, Council Members Mike Baxtley,
Mike Reitz,Julie Whaley,Tim Reed, Ginger Thomson (arrived 4:10 p.m.) and Tom Bezdicheck.
City Manager Alan Lanning, City Attorney Steve Britzman, and City Clerk Shari Thornes were also
present.
Storm Draina�e. Troy Thompson,President of Ecological Consultants out of Evergxeen,CO,
provided a presentarion to the Council on storm drainage issues. The City is currendy developing a
dtainage manual for the city.
Drainage runoff resulting after a rainfall event in undeveloped land results in the majority of water
infiltrating into the ground to recharge groundwater. Watex that doesn't infiltrate ttavels slowly
across the land until it enters a defined channel.
How does development effect storm water drainage? Development increases `impermeable'
surfaces such as roads,roofs and pavement that water cannot infiltrate. As a xesult,the amount of
water that tuns off as surface water increases. Development decreases the time it takes for surface
water to travel by channeling flows in swales, sewers and roads. The amount and rate of runoff
increases as a result of development.
(I'homson arrived at 4:10pm)
What happens as additional development occurs? Old clrainage systems are no longer adequa.te to
handle the additional development runoff. Downstream drainage systems axe often overwhelmed.
Runoff from a development should be controlled so that the rate of runoff after development is no
greater than the xate of runoff from the land's pre-development condition.
There are two ways to accomplish this:
1) Storm Water Detention—Build a facility that collects and detains stonn water and releases it
downstream at a rate equal to the predevelopment condition.
2) Storm Water Retention—Build a facility that collects and retains storm watex and does NOT •
release the water downstream. This is typically done when a development parcel has no
historic oudet or xeleasing water will harm the downstream owner.
What detention will mean to the ciry? Advantages include gready reduced flooding in the city and
associated hazaxds and costs; cost savings from system retrofits; and development pays its own way
in terms of drainage. Other considerations are initial cost increase for development (lost lots) and
the system only works if properly maintained.
Detention works through allowable outflow, stoYage volume,outflow, and inflow keeping people
downstxeam from seeing the overflow in a hazardous manner.
Detention is designed for two design events: minor storm (5-yeax) and the major storm (100 year).
Oudets from detention ponds axe designed so that releases given developed conditions match
natural flows in undeveloped conditions.
Options for development planning include:
1) Loca1 detention required at each individual development
o Advantages:
■ easiex to xegulate in terms of timing&responsibility
■ equitable solution—development pays its way
o Disadvantages:
• more facilities to mainta.ui and associated long term costs
■ lost economies of scale when building facilities (infrastructute costs with
piping / gates / land / less for multiple axeas)
2) Regional detention built that can be shared by multiple developments
o Advantages:
■ fewer facilities to maintain
■ economies of scale—cheaper&less land
80
o Disadvantages:
■ difficult to plan what land will be used
■ need to first site whexe detention would go
■ big issue is it is typical to have different land owners
■ owner of pond site is at a disadvantage—not very equitable
■ cost equiry can be difficult
■ difficult to implement
• requires a comp master dxainage plan
Thomson's xecommended implementation:
o New development and redevelopment will required detention or retention,
o Drainage plan submitted as paxt of typical development submittals,
o Specific calculations methodologies outlined in the storm drainage manual,and
o Results should gready improve current drainage problems not compounding problem by addi.ng
more development upstream.
Qaestions/Comments
Jim Flippen questioned what the preferred approach was. Thompson said detention was the
preferred method.
Keith Rounds asked how the structures wouid get implemented in the system. Thompson said it
would be done ovex time looking at the pxoblem areas of town and their hydrology. Road
overtopping and different structures are impacting the current flow of water. Key elevations need to
be identified. He cautioned the approach must be holistic so that a good benefit to cost and not
wanting to fix upstream problems only to create increased downstream flow related problems.
Jim Flippen asked if the manual or study would include 6 Mile creek,closing the channel and xouting
through town. No,FEMA is studying 6 Mile Creek. Our drainage basins are on the south part of
Brookings. The City has asked FEMA to study areas near Brookings. They will generate digitized
maps that they will make available to the City.
Ted Egebraaten,Brookings County,asked how far would they address drainage downstream ftom
these applications. Thompson said they would need to go downstream far enough so we don't have
back water impacting water levels.
Brian Gatzke asked what the esrimated costs would be to developers and home buyers. There .
would be associated costs in losing usable square footage on the property (i.e. 1 in 501ots). That
would depend on density of lot, size of pond, and size of development. This will have benefits to
the homeowners and development in that no one will be able to build upstream and flood them out.
There is an upfront cost that is passed on to homeowner. In the long term, the homeowner would
be moxe insulated from drainage problems and flooding.
Keith Rounds asked how to analyze an impact developing downstream and 70 acre development
ahead of you. In that case the upstream developer has already changed the flow xate thxough his
property. At what point do you go back to historical data? In the case of Brookings we are not
staxting from scratch. It is impoxtant to dxaw the difference between historic and undeveloped.
Historic condition is looking at what is there now.
Munsterman asked who pays the costs -developers or sharing of the public. In the case where the
city has a regional detention system with a master plan studies,governmental entities bear the cost
(i.e. DenverMetro area). If the city has developments not located on a ma}ot drainage channel,like
Brookings, the developer pays. Brookings fits better into a local detention approach. Regional is a
gxeat concept but the timuzg is almost impossible. All developments have to be planned and the
drainage built.
Bartley asked if part of oux study would address retrofit costs in addirion to local detention.
T'hompson said it will look at the criteria for how to design drainage facilities and look at planning
bigger drainage facilities.
Jackie Lanning,City Engineer, said the city is looking at city owned property that could be
retrofitted in addition to localized detention by developers.
81
Bartley asked what exactly is the City trying to achieve—a 5 or 100 year plan? When will we have
that discussion and at what level do we spend the money? Thompson said those are two typical
benchmarks (minox and major) consistent with FEMA standards.
Brian Gatzke asked if the ciry was stopping development on these subdivisions. How is the city
addressing planning on laying out plats? This is a cost that must be addressed. Developers will have
risks as they continue to develop lots.
Jackie Lanning said subdivisions are in different stages, some already in drainage sta.ges. This
criterion will be used to identify the calculations. Platiing would occur in the same fashion with
more drainage requirements in the preliminary plat.
The Planning Cornmission will discuss the manual at a meeting later tonight. Thompson will return
in April for more meetings with the public. The manual will be revised with another draft available
fox Council and public input.
Kathy Rounds stated thexe is a need for this issue to continue to get public input,particularly for
those financially impacted. Right now there are developments adjacent to each other owned by
different corporations some up and some downstream. The ideal thing doesn't e�st. With those of
us down stream from development that wasn't as completely planned for storm water as it could
have it will be critical befoxe furthex development (retrofit) because the growth has been so rapid.
Everyone wants to wotk together and solve the pxoblems.
Proposed Ordinance on Falcons/Hawks. A motion was made by Reed,seconded by Whaley,to
introduce the topic of an ordinance first reading that allows for falcons and hawks within city limits.
All present voted yes;motion carried.
Adjourn. A motion was made by Whaley, seconded by Reed,to adjourn. All present voted yes;motion
carried. Meeting adjourned at 5:07 p.m.
Ciry of Brookings
�,jv o�� Scott . unstexman,Mayor
a.���-�
z; �A Y`•;s
lg�9
:�
l
c�'c�. �,•'�o�
a S� .�P �/ ll//
hari Thornes,Ciry Cle