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

1601 Blake Street, Suite 200
Denver, Colorado 80202
(p) 303.572.0200
(f) 303.572.0202
www.matrixdesigngroup.com
MEETING MINUTES
Sanderson Gulch
Major Drainageway Plan and Flood Hazard Area Delineation
Tuesday August 21, 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
Mike Anderson Denver Capital Projects 720-865-3023 mike.anderson@denvergov.org
Jeremy Hamer Denver Capital Projects 720-865-3023 mike.anderson@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
1. Previous Action Items:
a. Matrix to set first meeting on Hydrology in 4 weeks – done
b. Matrix to set up website – done
c. Matrix to review new updated DFHAD Guidelines – done
d. Matrix to check the map labeling of Clairefield Reservoir – done
e. Matrix to distribute the basin map electronically – done
f. Matrix/Denver to check if all CCD Parks data is available in GIS – done
g. Matrix/Denver to set a van tour – extend the tour into Lakewood – done
h. Lakewood/Denver to get contact info for ditch companies – open. Information has been provided,
but the ditch companies have not been contacted to-date.
i. Lakewood to check on easements along private sections of the gulch – done
j. Denver to ask their bridge group if any bridges have structural issues – done
k. Denver to confirm desired capacity for street crossings – done
2. Baseline Hydrology
a. Basin boundary delineation
i. New model has 101 sub basins – 94 in Sanderson Gulch and 7 in Mississippi Gulch
ii. 1972 model had 20 sub-basin. These sub-basins are larger than the recommended
average size of 100 acres.
iii. Shape factor and design point inflow are reasons for further subdividing basins
b. Basin parameters
i. Impervious & pervious retention loss
1. 1972 hydrology used an infiltration of 0.75 inches/hour. This does not equate to
parameters used in the current model following Horton’s infiltration parameters
2. 1972 pervious reported as 0.3 in the text, but example sub-basins used 0.1
ii. Infiltration loss (Type C soil used throughout) – based upon Lakewood data. Type C
soils will be assumed throughout the entire watershed.
iii. Imperviousness City of Denver Land Use Data, City of Lakewood Land Use data and
Future Green Gables Plan
1. Average in 1972 was 40%
2. Average for the updated study is 51%
c. Rainfall
i. 1972 rainfall varied by sub-basin
ii. 1972 MDP rainfall distribution curve compared with current USDCM
iii. 1972 modeled a 2-hour storm with a lower peak value for 100-year
Sanderson Gulch Minutes August 21, 2012
iv. Rainfall distribution criteria shown for Denver, Lakewood and USDCM
v. Recommend using one rainfall for the entire watershed following USDCM
d. Hydrograph Routing
i. Channel cross section measured from topographic mapping
ii. Crossing structures at basin boundary modeled with overflow elements
iii. Trans-basin flow – water imported into basin by pipes and roadway
1. Federal Blvd
2. Mississippi Gulch Basin
iv. Detention modeled in the following reservoirs:
1. Smith Reservoir
2. Kendrick Reservoir #1 (not in 1972 MDP because of 100-year capacity)
3. Kendrick Reservoir
4. Jewell Park Reservoir
5. Green Gable Entrance Road
6. Ward Reservoir #1 (not in 1972 MDP because of 100-year capacity)
7. Clairefield Reservoir
8. Bit-O-Sea Reservoir
9. Ward Reservoir #5 (not in 1972 MDP because of 100-year capacity)
10. Harvey Park Lake (not in 1972 MDP because of 100-year capacity)
11. Green Gable Park Reservoir
v. Findings regarding detention reservoirs
1. Smith and Kendrick have low level outlets - not only spillway
2. No rating curve chart was available for Smith Reservoir from 1972 study
3. New rating curve needed for modified Green Gables Entrance Road
e. Calibration
i. Steps 1 – Input 1972 basin parameters and rainfalls, except infiltration coefficients into
CUHP 2005. Using stage-storage-discharge curves from 1972 MDP.
ii. Step 2 – Adjusted infiltration decay coefficient to 0.00111and adjusted Cp to reproduce
peak flows at comparable design points. Adjusted the stage-storage-discharge curve
for each reservoir to match the release peak flow in 1972 Study.
iii. Step 3 – Adjust rating curves for detention ponds to match outfall with inflow. The
1972 study reported detention volume, but the actual stored volume was larger. There
are 3 with rating curves that do not match 1972 results.
f. Duplicate Effective Results
i. Results of duplicate effective model are a good comparison with 1972
ii. Hydrographs prepared showing matching the peaks
iii. Time of concentration good, except North Sanderson peak time calculated to be longer
and outfall is calculated to be shorter.
g. Corrected Effective Model and Preliminary Results
i. Change imperviousness
ii. Replace rainfall in the CUHP 2005 using up-to-date information
iii. Correct detention pond rating curves using available topo to determine storage volume
iv. Need to get corrected model from Green Gables
h. Preliminary Model Results
i. 4142 cfs vs 3350 cfs at outfall, but using incorrect rating curves from 1972
ii. Concerned about Smith Reservoir in is 85% higher
iii. How does Horton infiltration affect the numbers?
iv. Need to check time of concentration. Look at a comparison from Sheridan Blvd to the
South Platte River. Why is the time of concentration now shorter?
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