Final Baseline Hydrology Report - October 2012 - Urban Drainage ...

1601 Blake Street, Suite 200
Denver, Colorado 80202
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MEETING MINUTES
Sanderson Gulch
Major Drainageway Plan and Flood Hazard Area Delineation
Monday October 15, 2012, 10:00am – 11:30am at UDFCD
Attendees:
Shea Thomas UDFCD 303-455-6277 sthomas@udfcd.org
Bill DeGroot UDFCD 303-455-6277 bdegroot@udfcd.org
Terry Rogers Lakewood Engineering 303-987-7934 terrog@lakewood.org
John Paliga Lakewood Community Devm 303-987-7815 johpal@lakewood.org
Mike Anderson Denver Capital Projects 720-865-3023 mike.anderson@denvergov.org
David Marquardt Denver Parks 720.913.0629 david.marquardt@denvergov.org
Kevin Lewis Denver Public Works 303-446-3658 donald.lewis@denvergov.org
Robert Krehbiel Matrix Design Group - Eng 303-572-0200 robertk@matrixdesigngroup.com
HungTeng Ho Matrix Design Group – Eng 303-572-0200 hungteng_ho@matrixdesigngroup.com
Jane Kopperl Matrix Design Group 303-572-0200 jane_ kopperl@matrixdesigngroup.com
George Slovensky Matrix Design Group 303-572-0200 george_slovensky@matrixdesigngroup.com
Bob Eck Matrix Design Group 303-572-0200 bob_eck@matrixdesigngroup.com
1. Previous Action Items:
a. Matrix to change the rating curves of detention ponds for Corrected Effective model to actual
conditions. Done.
b. Matrix to check time of concentration to understand the model results. Done.
c. Matrix to gather corrected effective model for Green Gables. Open.
d. Matrix to contact the ditch companies in this study area. Open.
e. Matrix to compare the 10-year gage analysis with the modeled 10-year hydrology. Done – See
summary at the end of these minutes.
f. Edit reach map to add reach 12, add street names, and move reach divide at the confluence and in
Kendrick Lake. Done.
g. Terry Rogers to arrange a van tour of Sanderson Gulch in Lakewood. Done.
2. Schedule
UPDATED SANDERSON GULCH MDP & FHAD SCHEDULE
(dates revised from the kickoff meeting minutes are shown in red)
Public
Draft / First Comments Final/Second
Meeting
Baseline Hydrology Report 8/27/2012 10/04/2012 10/25/2012
Selected Plan
Alternatives Analysis 11/19/2012 12/10/2012 1/4/2013 January 2013 1/28/2013
Concept Design 3/25/2013 4/15/2013 5/6/2013 April 2013
FHAD
11/5/2012
First technical
review only to
UDFCD.
11/26/2012
12/17/2012
Distribution
to Sponsors
3. Review Baseline Hydrology Report Comments
a. Statistical Gage Analysis – the computed 10 year discharge based upon the gage data is lower
than model discharges. This validates the calibration approach to adjust the raw model factor Cp
to lower the model flows to the 1972 values with all other model input the same. FEMA accepted
the hydrology in 1972 and the gage data is not giving us any reason to increase the hydrology
because of the newer models. It is important to note that actual hydrology will generally always
Sanderson Gulch Meeting Minutes October 15, 2012
be less than model hydrology due to small on-site detention ponds not considered in the regional
model, along with undersized inlets and other minor losses not considered.
b. Irrigation Ditches Impacting Transbasin Flow - Transbasin flows could occur between Sanderson
Gulch and Weir Gulch. The Agricultural Ditch diverts flows between Smith Reservoir (within
Sanderson) and East Reservoir (within Weir). It appears that it might depend on the WSELs in
each of the reservoirs to know which way the flows would go. This is discussed in the 1972 study.
Runoff from the upper Sanderson Gulch is intercepted by Smith Reservoir, an irrigation storage
reservoir owned by the Agricultural Ditch and Reservoir Co. The Smith Reservoir spillway directs
overflow into an irrigation ditch flowing into East Reservoir which is located in the Weir Gulch
Basin. This is effectively a transbasin diversion which would convey stormwater to the Weir
Gulch basin during overflows of Smith Reservoir. If this discharge is allowed to continue during a
major storm event, the effect would be to continually increase the inflow to East Reservoir into
Weir Gulch. It will be important to understand where emergency overflows for the ditches are
planned.
c. Green Gables Road Detention – The Green Gables redevelopment project is moving ahead. A
CLOMR has been submitted to UDFCD. The Baseline Hydrology model should match their
design release rates.
d. Mississippi Gulch – The baseline model imports only the capacity of the existing pipe into
Sanderson Gulch. A FLO-2D model to assess flows either following or crossing Mississippi
Avenue from Clay Street to Pecos is not necessary at this time. The Alternatives Analysis will
explore options to leave the allowable capacity in Mississippi Avenue in a major event and
convey the remainder to Sanderson Gulch.
e. Water Quality – Water quality to be discussed as a subsection in Chapter 2 Reach Descriptions
and also in the Alternatives Analysis section
f. Maintenance - Lakewood has easements for North Sanderson Gulch from Pierce to Florida
4. Alternatives Analysis Approach
a. Hydrology – Look for opportunities to reduce the hydrology (Detention)
i. Jewell Park Pond – Good opportunity to reduce flows into the King Soopers pipe at
Jewell and Wadsworth
ii. Carmody Park Pond – May provide a little benefit
iii. Green Gables Entrance Road – Match the design flows in the CLOMR. No opportunity
for additional detention beyond what is planned.
iv. North Sanderson Greenbelt Improvement Wetland Pond (near Lamar Street). This area is
not an opportunity for future detention.
v. Clairefield Reservoir – The surrounding area is planned for future ballfields. This area is
known as “Wilson Family Park.” The proposed ballfields could be set at the 25-year level
or some other event to shave the peak off the 100-year flood. The fields cannot be flooded
frequently. Lakewood to address the allowable frequency of flooding.
vi. Irving Street – Could provide some marginal storage for peak shaving. Doubtful that this
area could be regraded.
vii. Garfield Lake – Currently not providing any benefit in the model. To account for some
attenuation would require a formal agreement for a commitment to provide a detention
volume. Detention options could include formalizing existing conditions to provide
attenuation, or rebuilding the outlet to provide formal detention.
viii. Huston Lake - Currently not providing any benefit in the model. To account for some
attenuation would require a formal agreement for a commitment to provide a detention
volume. Detention options could include formalizing existing conditions to provide
attenuation, or rebuilding the outlet to provide formal detention.
b. Flood Control – Examine options to remove structures from the floodplain. Use FEMA’s model
as the preferred method to evaluate Benefits to Costs.
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