HomeMy WebLinkAboutCCMinutes_2008_06_17 13 �
Brookings City Council
June 17, 2008
The Brookings City Council held a special meeting on Tuesday,June 17, 2008 at 4:00 p.m., at City
Hall with the following members present: Mayor Scott Munsterman, Council Membezs Mike
Bartley,Ryan Brunner,Tim Reed, Mike McClemans, and Tom Bezdichek. Council Member Julie
Whaley was absent. City Manager Jeffrey Weldon, City Attorney Steve Britzman, and Deputy City
Clerk Bonnie Foster wexe also present.
Brookings Storm Water Draina�e Master Plan. Ciry Engineer Jackie Lanning opened with the
following: `7'd like to Zhank the Mayor and City Council far holding thi.r.rpecial u�ork.re.r,rion on our drainage
Master Plan. Fir.rt, I'd like to intrnduce Trny Thomp.ron, avho is p��zdent of Ecological I�e.rource.r Con.rultant.r
(EKC) of Evergreen Colorado and i.r here with u.r today to go through the re.rult.r of the ma.rterplan. I'll start o�with
.rome hi.rtory on avhat we have accompli.rhed with drainage improvement.r up to thi.r point, and then Troy urill pre.rent
the ma.rter plan.
During the.rummer.r of 2004 and 2005,Brooking.r had experienced.rome heavy rainfall,r, and City ManagerAlan
Lanning and I had looked at.reveral area.r of Brnoking.r that.reemed prone to fdooding. Alan had worked on drainage
project.r�rith EKC in the past, and we brought Trny to Brooking.r in June of 2005. One of the fir.rt thing.r Tmy
noticed�va.r that Brooking.r did not have a reguirement for detention. Detention zva.r a ne2v concept for many to�vn.c in
South Dakota, although it�va.r a common method of managing.rtorm�vater. Our fir.rtpha.re of work wa.r to develop a
Storm I�Y>ater Technical Criteria Manual, rvhich ERC worked on during the�vinter of 2005. We held contractor
and con.rultant meeting.r in the.rpring of 2006, and pa.cred new ordinance.r implementing the manual in Juty of 2006.
Al.ro thatyear, we heard that Brooking.r County had a contract for aerial phntngraphy. W/e partnered�ith the
County, and had had.rurvey point.r.ret throughout the City and the 3-mile area.ro u�e could have 2'contourr flown for
u.r. This�as a r�al benefit becau.re the County paid for the flying and the aerial photagraphy, and the City paid for
the contour mapping Both the City and County.rhar�the items�ve purcha.red�ince they�vere allpaid for zvith
taacpayer fund.r. By the lvinter of 2006, �ve received the contour map.r for our fir.rt.rtudy area, avhich wa.r e.rsentially
from the railroad track.r to the.routh city limit.r. In 2006, we adro de.rigned our fir.rt detention pond.ry.rtem, which
joined Timberline development and the Indian Hill.r development. In late 2006, the City Counci!raised the drainage
fee for 2007 to help pay for drainage improvement.r.
In 2007, we p�ceeded to build the Timberline and Indian Hill.r detention pond.r, which benefited all of the pmpertie.r
along thi,r.routhive.rt ba�in of Brooking.r. We alro had the contour map.r comj�leted for the re.rt of the City Iimit.r and
3-mile area.ro the.re could be encompa.r.red into the ma.rterplan for the entire city. Troy'.r.rta�vi.rited Brooking.r during
the.rummer of 2007 to take picture.r and note,r on area.r all over Brooking.r and.ret up the SuIMM model.
In the.rummer of 2007, the City Council di.rcu.cred having the cizy-wide ma.rter drainage plan completed a.r nne of their
goadr, and the draft ha.r corr�leted for thi.r ivork.re.r.rion. Tmy ha.r a pre.rentation thatgoe.r th�nugh the ma.rterplanning
prnce.r.r."
Troy Thompson,Ecological Resouxce Consultants (ERC), thanked the Council for having them
here and commented it has certainly been an interesting adventure to look at a]l the d.ifferent
drainage areas throughout town.
The process started two years ago when the City developed a Dxainage Criteria Manual. One of the
major concepts of the Drainage Criteria Manual was to look at retention or detention. With any
development or changes in land uses,it is important ensure that as new development occurs,
existing drainage problems are not becoming woxse. The next phase consisted of work on the
Master Drainage Plan. The concept with the Master Drainage Plan is to assess the city on more of a
macroscopic/large scale level and look at e�cisting and anticipated future drainage flows. Look at the
amount of water at different areas and generate the frame work for tackling existing problems.
The Master Drainage Plan assesses the cuxrent and anticipated future drainage conditions within the
City. The pla.n looks at drainage from a macroscopic perspective including major flow paths and
crossings. The plan quantifies existing and futuxe peak flow rates at key locations throughout the
city during what the city has defined as a minor stoxm,which is something that would happen once
every 5-years, and a major storm,which is something that would happen once every 100-years. It is
intended to be a tool that aids the city in planning,review of potential development and capital
improvements, and provides budgetary level estimates of costs to resolve anticipated major drainage
issues. It is not a city-wide,looking at every pipe, every sort of neighborhood level system.
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Thompson erriphasized the Master Drainage Plan is no way intended to supersede or get rid of the
Drainage Criteria Manual that the city has implemented,but rather compliment the drainage criteria
guidelines established by the city. It ptovides peak flow rates at key locations throughout the city
needed to assess future development and improvements. Detailed drainage planrung will still be
requited wit�i each development. Future designs should be compatible with the components of the
Master Drainage Plan.
If it is chosen to itnplement this plan, a more detailed evaluation will have to be done, as this plan
does not go to the full design level; optiinizing sizes of elements, setting elevations, figuring out
conflicts with utilities, etc. Cuxrently, there is a problem with someone setting up improvements or
developments when there al�eady are areas that drain onto that site. It would be very hard for
developets to estunate what kind of flows might be coming to their site frorn off-site areas. This
report will allow people to assess the types of impacts they have from upstream areas.
The model ERC has created is called EPA SWMM (Storm Water Management Model). SWMM is a
rainfall-runoff simulation model used to model single event simulation of runoff quantity. SWMM
generates runoff calcuIations from sub-catchment areas and routes them through a system of pipes,
channels and storage facilities. SWMM records runoff quantity from sub-catchments and calculates
flow depths and rates at each element of the model. SWMM provides `routed' hydrographs thxough
the drainage system. The model includes all the major crossings / all basin areas.
SWMM has several modeling requirements; 1) the rainfall events being looked at as per the city's
criteria for the S-yeax minor storm and the 100-year major stortn,2) Soil properties,impact, and
filttation capabilities, 3) Sub-Basin (land) parameters - slope,as the steeper the more quickly and
more runoff you get—percent impervious, the path for rainfall to infiltrate into the ground—land
use,park/undeveloped grass land allows water to infiltrate into the ground versus a paved parking
lot ox a xoof where the rainfall automatically tries to runoff those surfaces in a single-family
residential or commercial area—and depression storage,where there is storage of runoff before the
water flows out of the network, and 4) Drainage Netwoxk- areas or sub-basins that are connected
with channels,and in some instances storage elements where water is slowed down or detained.
The SWMM Model was generated fox both the minor 5-year event, and the majox 100-year event. A
5-year event is defined as 3.4 inches of rainfall within a 24-hour period. A 100-year event is defined
as 5.75 inches of rainfall in a 24-hour period.
The study area included all land within the city boundaries. It was broken into 35 areas based on
their major basins,including all outfalls from city property. Major basins were further subdivided
into minor basins; e.g. basin 20 was broken into areas 3, 4, 5, and 6. These 4 areas dxain to the West,
combining to a single outfall for basin 20. In addition to numerically numbexed basins, there area a
few in the southeast corner of the city that start with lettet`S';these are contained basins. Rainfall
that falls on a basin that starts with `S'is going to flow to a low spot within that basin. They will not
outfall fall from the city based upon cnrrent topography. All other numeric snb-basins will drain
and eventually leave the city.
Four Models were created to evaluate the drainage conditions for the city: 1) e�sting conditions
based upon e�cisting land use conditions, 2) planned future conditions, 3) future conditions witli the
100-year recommended impxovements to show that the iunprovements they axe listing in the xeport
would indeed be able to convey water out without flooding, and 4) a sensitivity analysis of the
dra.inage system to look at the unportance of maintenance of some of the existing facilities on the
overall behavior of the drainage system.
Existing Conditions Model. Land uses and developed areas within the city axe continually changing
as a result of new construction and zoning changes. This model takes a snapshot of the city to be
used as the base;existing conditions based upon the Vision 2020 Land Use Manual. The snapshot
included the following completed and anticipated improvements: detention ponds in Timbetline
Addition, detention ponds in Indian Hills Addition, future 15�' Street and Christine Avenue South
extension and the future 15`�'Street South and 7'''Avenue South extension.
Existing Land Use Model. In working on this model,land use was taken into consideration;how
much land is single £amily,how much is commexcial,how much is park/undeveloped, etc. Soil
types and how the areas interact was also evaluated. These land use paxameters were taken from the
Vision 2020 Plan.
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Future Conditions Model. The Vision 2020 Plan was used as the basis for this model. This model
looks at the city 12 years from now. The 2008 zoning map was used for areas that are currendy
undeveloped and evaluate what the intended zoning is for assumed future use.
Future Condirions with Recommended Improvements Model. This model views the drainage
situation in the year 2020 and assesses what types of drainage improvements are needed to be able
to convey the major 100-year storm event. Improvements were recommended for areas that
showed the possibility of flooding.
Sensitivity Analysis of Maintenance Model. Needing to consider the ongoing operations and
maintenance of such facilities is a very important piece to whatever the city plans to do with future
drainage impxovements. This model looked at the ability for a grassed channel to convey water.
They compared what a cleaned out/maintained grass channel would do and how much water could
be conveyed,versus a situation where you have grass channels that are over vegetated.
S�ecific Study Areas
In addition to looking at the ciry as a whole, there were some specific study areas identified by the
city as areas with existing dtainage concerns that would requite more detailed analysis. They
analyzed these 12 areas for the 5-year and 100-year storms.
ERC developed a model that looks at these areas in gteat detail. Looking at a drainage system on a
point-by-point location is not the best way to approach drainage problems. There are so many
places through the drainage system where you effectively have botdenecks;water might be flowing
from one spot, creating a flooding location. The approach of trying to fix site specific problems will
most likely move that problem downstream. Therefore,not alleviating any problem;just shifting the
location of the problem.
Z"his model does have some limitations. Master Drainage Planning looks at the city macroscopically.
This study does not go down to looking at every size of every pipe that is in the city, and it doesn't
look at where flows are going into different roads,but rather looks at major drainages anci major
crossings. The topographic mapping the city had obtained was very helpful in the study;it saved
them a lot of time that would have been spent on surveying. It does have some limitations,basing
all of the analysis on 2-foot contour intervals,but generally works very well. There are a couple
places with off-site drainage that runs into the city property,particularly from the North,where
there are areas which the future land use is not necessarily known and creates a bit of uncertainty.
Si�c Mile Creek does not have a detailed FEMA-type analysis done to evaluate its flooding. There
could be areas they've gone through and done their evaluation, determined size of culverts, etc., to
safely pass the flow from the city downstream,but that has not evaluated what potential flooding S�
Mile Creek could do.
When there is flooding in a very isolated area,the peak floods wouldn't coincide with peak floods in
a river, as it takes longer for xivers to reach their peak stages, so there is a litde bit of a benefit in
that. The study they are performing is different than backwater or flooding from Six Mile Creek.
There could be some combined effects from Six Mile Creek that are not considered in this study.
This study is looking in terms of major crossings,not neighborhood level analyses.
A Master Plan will give guidelines or big flow parameteis, and will allow assessment of major road
crossings, etc. As development occurs, or there is a change in land use at a certain area, there would
need to be an additional drainage report; similar to what is done now with all of the developments
having drainage reports as part of their submittals. This is what is called neighborhood drainage
level;installation of new pipes large enough to carry the flows. This plan is not in any way intended
to take the place of the types of drainage plans that the city is currently obtaining from development
projects.
Model Results -Area General Parameters
This following graph shows a summary of things that force the results to do what they are doing.
There are 28 different major drainage areas and the self-contained basins S56, S57, S68, S60, S61,
and S138.
Total Area Percent Imperviousness Curve Number
Area
(actes) Existing (%) Future (%) Existing Future
1 954.2 31.4 45.6 80.7 83.2
2 144G.7 25.2 38.2 78.3 80.6
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3 440.2 45.2 47.1 78.9 79.2
4 126.2 62.9 63.8 87.1 87.3
5 297.4 50.7 51.8 85.1 85.3
6 217.3 53.9 53.9 86.1 86.1
7 31.7 11.4 48.4 76.3 84.9
8 17.8 12.1 12.1 76.5 76.5
9 41.9 20.9 44.7 78.5 84.0
10 10.7 2.0 54.7 74.0 84.9
11 9.8 2.0 49.0 74.0 85.0
12 17.3 90.5 90.5 89.0 89.0
13 73.7 44.7 73.6 81.8 88.4
14 9.5 81.3 81.3 88.9 88.9
15 20.2 80.2 80.2 90.5 90.5
16 451.9 36.3 72.2 80.5 88.1
17 133.3 59.4 73.7 85.3 87.8
18 229.5 533 81.2 83.9 88.1
19 6.5 84.8 84.8 91.0 91.0
20* 4042.4 30.3 35.7 80.8 81.9
21 22.2 3.6 8.0 74.4 75.4
22 72.6 13.9 13.9 76.6 76.6
23 56.2 20.0 20.0 88.0 88.0
24 1 G.3 20.0 20.0 88.0 88.0
25 4.7 51.1 51.1 87.2 87.2
26 188.4 24.8 G4.8 78.5 89.7
27 5.4 23.4 23.4 88.4 88.4
28 12.4 39.8 39.8 80.0 80.0
S56 229.9 8.0 25.2 753 78.4
S57 40.2 6.0 3.1 74.3 74.3
S58 151.2 6.7 6.7 74.5 74.5
SGO 159.7 62.7 63.4 84.5 84.6
S61 157.5 27.1 43.8 83.0 85.5
S138 239.0 2.0 51.7 74.0 86.2
*Area 20 al.ro include.r Area 3,Area 4,Area S, and A�a 6 in thi.r table and in the
I��MM Madel.
This table shows the total drainage areas; e.g. area 1 has about 950 acres. Percent Impervious is
defined as how much of the basin does not let rainfall infiltrate into the ground. In area 1, 31% of
dYainage is occurs on roads,paxking lots, or whatever it may be where water is not able to infiltrate.
In the plan for development, that number jumps up to 45%; for the same rainfall event there will be
more runoff just because of that. The curve numbex utilizes land use,keeping in mind that areas
that were green space are possibly now developed differendy. As the curve number increases, so
does the runoff. A pxetty substantial change is in basin 11 going from 2%impervious up to 50%.
This gives you a good feeling for the magnitude of changes being looked at,versus changes in
specific locations.
Area Peak Flows
Q5 Q100 Q5/ACRE Q100/ACRE
Area Existing Future Existing Future Existing Future Existing Future
cfs cfs cfs cfs cfs cfs cfs cfs
1 897 1286 1768 2516 0.9 1.3 1.9 2.6
2 752 1225 1438 2432 0.5 0.8 1.0 1.7
3 475 500 981 1032 1.1 1.1 2.2 2.3
4 206 209 438 444 1.6 1.7 3.5 3.5
5 314 320 628 642 1.1 1.1 2.1 2.2
6 287 287 550 550 1.3 1.3 2.5 2.5
7 9 37 33 78 0.3 1.2 1.0 2.5
8 5 5 18 18 0.3 0.3 1.0 1.0
9 20 42 43 83 0.5 1.0 1.0 2.0
10 3 15 10 32 0.3 1.4 0.9 3.0
11 4 15 12 35 0.4 1.5 1.2 3.6
12 46 46 97 97 2.7 2.7 5.6 5.6
13 70 131 127 278 0.9 1.8 1.7 3.8
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14 25 25 53 53 2.G 2.6 5.6 5.6
15 54 54 112 112 2.7 2.7 5.5 5.5
16 449 813 847 1636 1.0 1.8 1.9 3.6
17 260 315 504 621 2.0 2.4 3.8 4.7
18 420 584 777 1133 1.8 2.5 3.4 4.9
19 24 24 40 40 3.7 3.7 6.1 6.1
20* 2997 3588 5928 6601 0.7 0.9 1.5 1.6
21 3 8 6 13 0.1 0.4 0.3 0.6
22 44 44 74 74 0.6 0.6 1.0 1.0
23 48 48 82 82 0.9 0.9 1.5 1.5
24 9 9 24 24 0.6 0.6 1.5 1.5
25 10 10 17 17 2.1 2.1 3.6 3.6
26 189 454 341 727 1.0 2.4 1.8 3.9
27 5 5 14 14 0.9 0.9 2.6 2.6
28 21 21 36 36 1.7 1.7 2.9 2.9
S56 50 167 175 320 0.2 0.7 0.8 1.4
S57 9 8 36 34 0.2 0.2 0.9 0.8
S58 53 53 176 176 0.4 Q.4 1.2 1.2
S60 215 217 435 440 1.3 1.4 2.7 2.8
S61 157 213 286 412 1.0 1.4 1.8 2.6
S138 21 465 35 843 0.1 1.9 0.15 3.5
*Area 20 al.ro include.r Area 3,Area 4,Area S, and Area 6 in thi.r table and in the S1�%MM Model.
The above table shows the calculated area peak flows. Area 1 has some development and goes from
31% of impermeable areas up to 45% for a 5-year flow. Area 1 has a 5-yeax flow outfall which goes
from 900 cubit feet/second (cfs) to almost 1,300 cfs. The 100-year flow would go from 1,770 cfs to
2,500 cfs. These kind of outflow numbers aren't typically seen, however the reason being is the city
has so many botdenecks in the system, that this flow is out there but it is not getting to a point
where water is conveyed to one area,but rather forcing localized litde flooding problems in many
areas.
These are normalized flows per acre of area fox flows occurring in both a 5-year and a 100-year
event. If there was a flow of 900 cfs,Area 1 has a drainage basin that was just undet a thousand
acres;this amounts to about.9 cfs/acre. This chart helps create an idea of which axeas axe most
heavily developed;a 5-year flow as high as 2.7 cfs/acre of area versus something much less
developed might be down as low as 0.3 cfs/acre. Bain 20 is includes basins 3-4-5-6 which all drain
into basin 20 as it drains out,which causes some very high numbexs for basin 20. Basin 20 is a
much larger area than all of the other drainage basins.
Big Sioux Flows
Thompson gave a comparison of what those area peak flow numbers mean and how big they really
are. He compared the nuxnbers to the daily flow data available fot the Big Sioux Rivex (average
monthly values). The flow of the Big Sio�R.iver is 1,100 cfs in Apri12008. Peak numbers on the
area peak flow graph showed some numbers that were above that 1,100 cfs range. The big
disconnect is the 1,100 cfs for 30 straight days on the Big Sioux River and the numbers you saw on
that last tables are 1,000 cfs for 5 minutes within the city. There is a very big difference between
peak flows and average flows,but it brings into pexspective how big some of these peak events
would be. The highest average daily flow of the Big Sioux R.iver on the highest day was back in
2001, although 2007 had some very high values.
The Channel Maintenance Model looks at future conditions and determuies what type of
improvements would be needed to pass the 100-year event flow thxough the city. All suggested
improvements were assumed to be in place,and any place they were conveying or just passing flows,
they assumed were going to be grass channels; something that would need more maintenance. If
these channels were over-grown,the amount of water that can flow through the channel was really
restricted;vegetation will basically work to block the flows. If the city designed and implemented a
system that would be able to pass the 100-year flow and then did not maintain that system,in about
1/3 of the areas, the channel with overgrown vegetation that was designed for the 100-year event,
wouldn't pass the 5-year event.
Thompson stressed if the city is moving towards some drainage improvements,it is not just the
capital costs,but also the need to maintain (the ongoing maintenance of these structutes) these
improvements, so that you actually get the benefit of what you are spending your money on.
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The recommended improvements aYe geared towards the ability to pass the 100-yeaY event (5.75
inches of rain in one 24 hour period). These recommended improvements consist of 5 things: 1)
Detention Facilities. A detention element takes water running in and holds it;think of it as a pond.
The benefit of any detention faciliry is that you have a big peak of watet coming in. If you have a
pond, that peak water wili come in, fills up that pond and the ponds effectively regulate the water
going out on the downstream end; there is more water coming in than going out. Detention can
drastically reduce the peak flow or the size requirements for any improvements downstteam.
Detention facilities effectively reduce the peak flow level by one-third. 2) Conveyance Elements
(ways to pass water). This included gtass swales, concrete channels,box culverts, etc. 3) Flood
Warning System. There are some areas where with really low spots and no practical way to get
storm water moving in to get out in a quick manner. The railroad viaduct is the main example
where you're stuck because there is a low spot, and instead of coming up with whatever type of
facility to try to fix that,you are probably better off just warning people during a flood event that
this is not the place to be. 4) Improvements in master plan limited to major areas only. 5) Eminent
Domain or other means to add moYe detention on cutrently developed pxopexty was one of the
things not looked, but may be more economical to the city. Adding detention where there may be
development now was also not looked at. Thompson commented as you look at where you want to
go and the costs and benefits of some of the drainage impxovements,you may choose to consider
eminent domain as something that makes sense from a cost benefit standpoint. If you could have
high up in the basin area a big detention pond that would drastically reduce the flow on everything
downstream,you would be able to save all kinds of capital costs on downsizing pipes. So, lets say
there was an area that without a detention pond up stteam,we've got 1,500 cfs coming in.
Everytivng downstream would have to be designed to pass that 1,500 cfs plus whatever additional
flows come in. If you could build a pond even bigger than those we looked at,maybe you could cut
that number in half. So instead of 1,500 cfs,you may be now dealing with 800 cfs going out and
much money for infrastructure passing 800 cfs versus passing 1,500 cfs could be saved. This is not
addressed as an option in this model,just something to think about
City staff identified four proposed detention areas. The locations of these were chosen based upon
areas that the ciry has property or the ciry has talked with landowners about potentially acquiring
properry. This did not get into the removal of any eacisting development.
Cost estimates were generated fox each recommended improvement,major drainage items. A full-
blown cost estimate trying to quantify all the earthwoxks and all the re-vegetation, and those types of
things was not done. Since most of the impxovements were conveyance elements ox channels or
culverts they determined what that cost was from estimates generated from known material costs,
bid documents pxovided by the city, costs for similar projects and engineering judgment. This is not
looking at every pipe in the system, only major drainage crossings, and the major improvements
required to pass these flows.
Costs stated are fox capital costs only and do not include all costs likely associated with drainage
unprovements. Costs that were not considexed included: easements that may be requited,property
acquisition that may be required,potential utility ox other conflicts,upgrading or facility between
majot drainage structures,upgrading of`neighborhood'level drainage features, and operations and
maintenance.
Assumed Minor Cost Items
• Site Preparation 10%
• Erosion,Water&Sediment Control 5%
• Minor Drainage Elements/Incidentals 20%
• Mobilization/Demobilization 5%
• Design and Permitting 10%
� Construction Management 8%
� Contingencies 10%
TOTAL G8%
Just those major items do not in any way encompass the true cost of the project. Other categories
they included were: site pxepatation (10%), erosion,water and sediment control (5%),minor
drainage elements that may include special fittings, orifice plates,incidentals (20%),
mobilization/demobilization for the contractor (5%), design and permitting (10%), construction
management (8%), and contingencies (10%). These percentages add an additiona168% to the major
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d�ainage items costs. For example, the cost for putting in a culvert is $100. The cost for that would
be$168 based upon adding that 68%.
Thompson stated in reviewing itnprovements for a 5-year event and a 100-year event,if the system
overall is not improved to these levels,all these improvements will do is move the problem onto
somebody else.
In the case of study area #1,you are looking at 5-year storm if we can use detention ox no detention,
then the 100-year with or without any detention. Study area #2, here we have zero cost. That
doesn't mean that you don't have a problem,which means that based on the information that's out
there right now, there is no way to define something that works. The problem there is that the pipe
things are going through is what's called surcharge. The problem is somewhere downstream and
water is backing up to come in and cause a problem here. So without a detailed analysis of that
whole piping network, they really could not assign what improvements would work for that area.
Move on to the next one that talks more about the major drainage areas, the 35 that they have.
T'hey ase not talking about small dollars.
Overall,in looking at the 5-yeax and the 100-year, there is pretty much at least a factor of 2 in costs.
While they don't have this for the ovetall city-wide xecommendations,where they would say in this
case,looking at improve things to the 5-year storm with retention versus the 100-year storm with
retention,it is 3x more expensive to improve to 100 year. In some cases,it is not that dramatic. In
study area #3, $60,000 versus $110,000. As a general rule of thumb,what they are seeing here was
at least a factor of 2 going from 5-year improvements to 100 year improvements.
a ital Im rovement Costs
Recommended Recommended
Area Im rovement Cost Area Im rovement Cost
1 7,525,529 19 0
2 14,618,706 20* 11,649,446
3 5,281,497 21 0
4 1,697,932 22 0
5 2,863,555 23 0
6 �,379,474 24 0
7 3,517 25 0
8 0 26 0
9 0 27 0
10 0 28 63,993
11 0 28** 276,341
12 0 S56 0
13 117,980 S57 0
14 0 S58 0
15 0 SGO 0
1 G 426,988 S61 0
17 0 S138 0
18 134,735 138* 276,341
Total 34,540,894
*Thi.r cost include.r the co.rt.r orArea.r 3-6.
**Thi.r co.rt applie.r of S 138 doe.c not have adequate rtorage. It was not
ncluded in the total cost.
The total of$34,540,894 for Capital Improvement Costs is not an accurate representation of all
costs,because of how sub-basin 20. Basin 20 is the latge basin thtough the heart of town that takes
flows from sub-basins 3-4-5-6. The costs for basin 20 include all the costs for basins 3-4-5-6. It is
done as such so if the city wanted to focus on basin 4, they would know those costs versus the cost
for basin 20,which includes basin 4. As a reminder, this dollar amount does not include the interior
piping systems,only major crossings. With minor improvements needed in addition to this, this
number is going to expand and is obviously going to be a very big number.
Cost Breakdown
Im�rovement T��e Percent of Total
Concrete Box Culvert 68%
Rectangulat Concrete 24%
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Detetirion 4%
Flood Warning System 0.04%
Grass Channel* 0%
Storm Sewer Pipe 4%
*In in.ctance,r ivher�item.r had more than one recommesrded impmvement, the ca.rt for a conc�te channel wa.r
u.red.
In breaking down the unprovements based upon type,in the long run detention may be more in the
best interest of the city. Curxently, there are only four areas that they looked at for detention. In the
total cost, detention is only 4%. Thexe is the Flood Warning System which is also a very small
ove�all percentage. The rest of the improvement types are ways to convey flows. Ninety-Six
percent of these total costs are just ways to move water from point A to point B. The Grass
channei shows up as 0% cost, as in all locations that could be a grass channel,a concrete channel
can be installed,which is more expensive to build. Concrete is more expensive,but considering the
ongoing maintenance with a grass channel,it is a cost benefit to look at. The grass channel at 0%is
anything that could have been grass has been accosted out as a concrete box. T"hey are only
assumu�g concrete in those Iocations.
General Recommendations. What the city is already doing with requiruig retention and detention is
important to continue. If drainage problems are not taken care of locally, at whatever that
development site is, those peak flows are increasing by 40% by the year 2020. By always requiruig
detention and retention on site, future conditions could look a lot like e�cisting conditions. Some
places won't be able to retain or detain flows,like a front yard that runs out into the road. The
future will nevex be able to look exacdy like e�sting from a drainage standpoint without doing some
other measures. Moving forward,you want to do everything you can to make sure the peak flows
don't get any wotse than they are right now.
Regional detention is not recommended. Regional ponds are created when there is currently a
detention pond, so a developer doesn't want to build another detention pond, but rather utilize an
existing detention pond, thus naming it a regional detention. The city could use these regional
ponds to retrofit the situation for the areas that don't curxendy have any detention. You could use
these regional ponds to route e�cisting flows through, thus xeducing peaks from existing flows rather
than using any xegional ponds to reduce peak flows from future deveiopment.
Maintenance. In the model assessing channels that were sized for the 100-year event and finding a
lot of them couldn't convey flows from a 5-year storm if they were not properly maintained,
emphasis how important it is that to have an active maintenance program for drainage facilities.
There is difficulty in not only implementing improvements,but there are huge costs associated with
these unprovements as well.
How does the city move forwaxd with these or some type of itnprovements like these? One concern
is the amount of money available to spend and the best way to do that. In a drainage situation
where there's an upstream/downstream path,you can't very easily start upstream or even in the
middle and figure you are going to be able to fix the problem. All you are really doing in those
instances is moving the problem downstream. The logical way to implement any type of drainage
impxovement is to start at the downstream end,because as improvements are made you already have
the infrastructure below to get that water from upstream out of the system. Based upon current
land uses and future zoning, don't move all the way to the downstream end, but rather move part
way up, and at some point in the downstream end,it could be looked at as helping the county with
problems farther down the basin.
The iype of improvements needed is the largest thing that comes out of this plan. In the beginning,
looking at being able to detain or convey the 100-year storm was the £ocus,and maybe that's not the
tivng to be looking at. Maybe the city should be thinking that because of the magnitude of
improvements needed and the costs associated with them,maybe thexe's something else we should
be looking at, for example a 5-yeax storm. There's nothing that says it's a 100-year storm or nothing.
Possible Next Stens
• Requite improvements with all future development
• Decide to design improvements to convey the 5-year (or toner) rather than 100-yeat???
• Define priorities based on realistic budget
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• Likely need to approach drainage problem using a basin by basin approach to ensure all
improvements are compatible.
Some possible steps include: 1) Maintain e�cisting facilities,2) requixe improvements with all future
development, 3) decide to design improvements to convey the 5-year event rather than the 100-year
event, 5) define priorities based on a realistic budget. It's hard to say one particular atea is of
priority,pardy because of the costs associated with it. In moving forward with planning like this, a
likely or potential logical method would be to define some kind of a capital budget. If you would
say over the next 5 years you are going to have$3 Million, then maybe what you can do is look at a
plan and say what will$3 million achieve knowing it doesn't make sense to start on an upstream end
and work downstream. Maybe there's some amount that's the best benefit for a certain sum of
money and tackle the problem. 6) the likely need to approach drainage problems using a basin-by-
basin approach to ensure all imptovements are compatible. Most of those recommendations would
be major basin-by-major basin. The best benefit for the dollar is if you focus on one of the 35
basins. Of those 35, there were xoughly 15 basins with recommended improvements, so you might
say lets work with this problem and then this problem instead of trying to work with 6 or 10 litde
problems within each basin.
Council Ouestions
Munsterman asked in looking at the 35 major basins,is there a hierarchy of those basins? No, don't
read into the assigned numbers. There are 281ocations where watex leaves city property. Every
numeric area is an axea that has a dtainage path that goes out/away from city property.
Munsterman asked for clarification on the distinct drainage patterns of areas 1 through 6. 1"he
dtainage pattern of area 1 collects,dtains down and runs along the East Side of Medary. Area 2 runs
down the west side of Medary. Basins 3-4-5-6 drain to the west.
Munsterman asked if there are 3 major drainage patterns out of the 5. Yes,there are 3 main outfalls
from the system.
Munsterman asked for clarification on the costs. Axea 1 has a cost of$7.5 million. Area 2 has a cost
o£$�4 million. Areas 3-4-5-6 have a cost of$11.6 million. The 68%is already factored into these
numbers.
Bardey asked how flooding was defined;if it was water running across the street,backed-up in the
sewer,property damage, or just temporarily a car splashed through it until they got to the other side?
Thompson stated these 12 axeas were identified by receiving specific complaints. The most severe
of these was in Area 4 where there's a small channel that goes through a parking lot. The report
indicated a car was actually moved, during a peak flow, down towaxds the outfall. Some may be
nuisance, and some may be every time it rains they have problems.
City Engineer Jackie Lanning asked Council Member Bardey if he was asking more about the about
the model and potential flooding areas on the mapping and how flooding was defined?Yes, the
severity of the ptoblem. Bartley stated he understands thete's a cost benefit analysis we'xe going to
have to make at some particular point,but what he wants to understand is what the actual physical
damage or cost is. He knows it is inconvenient to slow down to drive on a flooded stteet once or
twice a year, but does that justify the 100-yeax or 5-year cost to improve that so we never have to
drive across the flooded street? He understands the viaduct is going to flood. It would cost a lot to
change that. We probably have more cars lost in the viaduct than we do anywhere else in town
because somebody made a wrong choice and tried to get through there. He feels we can solve that
problem with bigger barticades. T'he cost benefit to him is important to explain to the citizens of
Brookings. He asked what problems are we actually going to solve? He knows of some issues of
flooding some storage sheds by the airport on a constant basis of a 5-year storm. He would like to
solve that problem to a certain degree,but do we solve every one of these? He doesn't see a cost
benefit analysis in the report,but xather a supplementary report that could be handled by city staff to
help us make a decision.
Thompson agreed. When they identified flooding, they identified it showing the major submerged
crossings. Their ptogram can step you through a model of what happens,in increments of 5
minutes,with a 100-year storm. In the model,if an area is flooded out for more than 2 time steps,
.1 hours,it was nuisance. If it was flooded for longer than that they said an improvement should be
implemented, and an improvement was implemented in the model. If it was flooded,but for less
than that time period, they ignored that as a problem.
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Reed questioned in basin 20, area 4,in order to f�that problem,we also have to fix areas 3-4-5-6 to
solve that problem? Thompson stated not necessarily,but you want to be careful. You don't want
to just jump in at one spot and fix it there,you want to evaluate what is happening downstream.
With something like this you may say we don't want to improve it for a 100-year event,because we
know all that's happening downstream. You may find out that when you look at that system,you
can do some minor unprovements that will reduce the frequency of flooding. Reed commented that
the $11 Million would solve that problem, but there's probably a range of solutions up to $11
Million. Yes.
Munsterman asked for clarification of what areas make up the $11.6 Million number. It consists of
Axeas 3-4-5-6,with one minor impxovement in area 20 that is outside of axeas 3-4-5-6. The $14
mi]lion is a sepaxate number for area 2.
Weldon asked of dxainage axeas 3-4-5-6 and 20 drauung to the West,is that the dtainage ditch along
the railroad tracks heading west near the airport and by Rainbow Play Systems and does that
drainage ditch go to the Big Sioux River? Yes. Weldon asked then if that one drainage ditch is
handling all 5 of those drainage basins. Yes.
Reed asked Thompson if it would be possible to overlay the basin map and the flowing locat�ons.
Yes.
Weldon asked for classification of the 5-year and 100-year events. He stated it seems like we've
been getting a lot more fxequent heavy storms. A 100-year storm seems to be happening more
frequendy than just once every 100 years and he asked if climatologists are looking at climate change
as part of the cause, or is something in the industry looking at that to see if there's any changes
regarding classifications of events. Are there degradations of a 25-year storm,a 50-yeax storm,a 75-
year storm to help us figure out which appxoach inight be best? Thompson stated most of this
climate data came from work that was done by the NILA. What they do is split flows out for any
area, their maps will give you 2, 5, 10,25, 50, and 100-year events and it will bxeak those up from 30
minutes, 1 hour,24 hour increments. He doesn't think there's been any adjustment to the official
rainfall maps that would deal with more recent trends as far as changing long-term trends, or if we
just happen to be in a wetter cycle that will xevert itself back.
Munsterman asked Lanning in looking at those 6 axeas and their drainage pattexns (east of Medary,
west of Medary,west of airpoxt, etc.),what area has the most pxoblems? Lanning stated they have
the full view of what is going on with the ciry and some of the additional study areas given to Troy
based on pictuxes taken during 2-year and 5-year events and some localized flooding,which are all
separate from the full master plan. There was a situation with the 2.89 inch rainfall the other day,
where Sawgrass Drive and 15`'' Street South experienced some localized flooding. Localized
flooding makes her nervous because you could have property damage. In the 12 study areas she's
seen some critical situations that have come close to propetty damage. Lanning thinks�ooking at
areas 1 through 6 is best. In looking at the maps, thexe's some confusion where 3-4-5-6 drain down
through the tracks. Area 3 drains northexly on the south side of the tracks with one equalizing pipe
crossing north/south under the tracks. This pipe was cleaned out and is flowing as good as it can.
Area 4 flows on the north side of tracks. Area 20 runs more northexly and westerly instead of
e�ting southerly. More discussion and evaluation of these areas/basins is needed.
Reed asked Lanning if there is a maintenance plan fox these certain areas to be cleaned out, such as
under the railroad tracks. Lanning stated the pipe cleanout is a yearly thing. They have used the
drainage fee for maintenance of the storm sewex pipes. She feels our pipe system is fairly clean.
Recendy, she has done moxe of an ongoing visual of our drainage swales,as many of those around
town are vegetated. She was amazed to find out how the capacity could be enhanced by having a
better maintenance plan. She stated she will definitely take a closer look at using more maintenance
funds for regulax ma.intenance.
Public Ouestions/Comments. Doug Austreim,Austreim Landscaping. Austreim stated this creek
flows through theit property and is a major drainage axea for the city on the north side. In his time
in Brookings, the only time there had been evacuations in Brookings involved the areas around Six
Mile Creek. He feels it would be a mistake not to take a good look at that area as part of this entire
plan. ,
14 �
Munsterman stated he would like to have city staff look at the cost benefit analysis and analyze the
cost/unpact of 25-year, 50-year, and 100-yeax floods. He would like to see a look at the
maintenance program recommendations and come up with a short and long term plan.
Weldon stated this Dxainage Master Plan is clearly one of the council's eight major goals for the
year. Our Storm Drainage Utility Fund raises about$400,000/year at the current rate. Part of it has
to go to maintenance, so it is going to take us a long time to get to that big dollar amount on that
sheet if we are going to try to tackle that. Weldon thinks we need to strategically take this study and
break it down into its various components, specifically the 12 identified areas, and look at a cost
benefit analysis on each one, and try to put some corresponding dollars to that and figure out a
priority basis how much of this we want to bite off, as well as intervals in terms of time, as this is
clearly a multi-year project to tty to resolve.
Weldon stated one important disclaimer is if the city has a major flooding incident,not a 100-year
flow,but a 500-year type of event, there ase some cases you cannot build systems and structures big
enough to handle every eventuality. You can't build a system big enough to handle every flooding
catastrophe. He stated we need to be thinking along the basis of how much axe we able to live with,
how much can we tolerate and how much can we try to build with what we can afford. With the
consultants help we will be able to dissect this and be able to come up with a plan that makes a lot
of sense. Weldon suggested holding more public hearings in the future to talk to the community,
the neighborhoods, and the developers about these issues. He thinks the fitst thing is to continue to
do what we have done in the past in terms of subdivision regularions with managing it at the
localized level and we can always tweak those technical manuals if necessary.
John Moriarty commented he has spent 87 years watching the ciry grow and watching the city flood.
He thinks it is wonderful how Bxookings has been taken care of over the years,but feels the
problem is really larger than these small little areas we are talliing about. He stated there is one area
from the tracks north,another area from the tracks south, then there is Timberline, around the
cemetery,and Indian Hills that all flow to the south. He stated that somehow we have to figure out
how we can get this water to the Big Sioux R.iver. The farmers to the north had a problem with
Deer Creek. If you drive west of town (Brookings) about two miles, the channel that goes one mile
west of Cameron's Corner flows south to the Big Sioux R.iver. The other channel goes through the
land that is Six Mile Creek. He explained there are two channels with S�Mile Creek; the deep
channel is to the north of the fishponds, and that channel was filled in by the college and it all flows
south into the south channel. No water will go into the north channel until the south channel gets
filled up by the bridge by the Bowling Alley, then it starts to go to the north. He feels the other
problem is when water goes from Timberline, down past Mike McClemans place. He commented
on the holding ponds there, that they are fine and good for mosquitoes,but when it goes south,it
has to fill those,before the water goes out. He knew the city bought some of Mills' property fox a
holding pond on Medary Ave. South,but most of that water goes on the east side of the road and
floods 120 acres by the old airport. He asked why do we stop there,and why don't we keep going
so the water can get to the Big Sioux River. He commented it was nice to ha�e somebody from
Colorado come to South Dakota with our fladands,with no hills or nothing, and tell us how to do
this. He thinks that young man did a fine job,but lets remember we've got flatland... no
mountains,no snow on the mountains,just flat land.
Thompson clarified with prioritization and the need to start at the downstream end and work
upstream when you are doing something. You don't start in the middle and have downstream a.teas .
that cannot convey the flows. The defuute part of any improvement that would be opposite of that
is detention. If you can add detention basins the further upstream you can add them,the more
improvements you get further downstream. He said if you have money,you want to start
downstream and work upstream, that's true for the portions of your improvements whexe you axe
conveying watex,but any place that you could detain and hold water,the further upstream you could
do that, the bettex.
Bardey asked Weldon if it would be appropriate for the Council to set some sort of deadline here to
approve this Master Drainage Plan in its draft form. Bartley would like to see getting this adopted as
soon as possible. He feels it has taken a long time to get to this point, and thinks the first step is to
adopt this in its final form and move forward with a moxe localized study as necessary. He asked if
there was a time frame that would woxk well in adopting this...3 months, 6 months?
Weldon clarified this plan is in draft form. He asked Thompson what information is needed from
the city to make a ftnal document. Weldon stated he would rather bring the document back to the
council for final adoption and dive into the specifics aftex that.
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Thompson stated they are not waiting for any more information from the city other than if there's
any feedback on the document itsel£ It is a lot of information to digest in a short amount of time.
If they get the go ahead to finalize,it would be just a couple weeks.
Munsterman stated the council will put this on a £uture action agenda.
Executive Session. A motion was made by Bartley, seconded by Reed, to enter into Executive
Session at 5:3$p.m. for personnel reasons with the City Council,City Manager, and City Attorney
present.All present voted yes,motion caxried. A motion was made by Bezdichek, seconded by
Bardey, to e�t Executive Session at 6:20 p.m. All present voted yes,motion carried.
Adjourn. A motion was made by Bezdichek, seconded by Bardey, to adjourn. All present voted
yes;motion caxried. Meeting adjourned at 6:23 p.m.
CITY OF BROOKINGS
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G�TY oFe Scott . Munsterman,Mayor
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S ari ornes,City Clerk