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Is It Stable Yet?A Lessons Learned Approach to Predicting Long Term
Stable Channel Slopes
2009 CASFM Conference
Crested Butte, CO. September 16 – 18, 2009
Alan Turner P.E., CFM, CH2M HILL J. David Van Dellen, P.E., CFM, Town of Castle Rock
Pieter Van Ry, P.E., CFM, Town of Castle RockMark Glidden, P.E., CH2M HILL
Page 2
Objectives
• Overview of the Castle Rock Master Planning process and history
• Development and implementation of the preferred stream stability methodology
• Philosophy and approach to CIP implementation program
• Potential stream stability cost savings for the Town
Page 3
Master Planning in Castle Rock
• Town characteristics– Steep terrain– Diverse soil types– Rapid growth
• Stormwater Master Plan - January 2004– Created Town
Stormwater Utility– Used to create master
planning and CIP implementation budgets
Page 4
Goals of Castle Rock Master Planning• Stormwater Enterprise
Fund Capital Improvement Program
• Development Guidance• Develop FEMA Compliant
Flood Hazard Information• Preliminary Wetlands
Inventory• Determine long-term
stable channel grade
Page 5
Available Methodologies for Stream Stability
• Regulation and Recommendations– UDFCD– Town of Castle Rock
• Approximate methodologies– Sediment Transport Calculations– Permissible velocity
• Detailed methodologies– HEC-6– HEC-RAS
Page 6
Traditional Permissible Velocity Analysis
• Looks at basin wide stream stability• Utilizes one stable channel grade based on
– Generalized soil conditions – Generalized hydraulic conditions– Generalized vegetative Cover
• Conservative one size fits all methodology
Page 7
Revised Permissible Velocity Analysis• Developed during the Omni, Industrial, Westfield,
and Dawson Tributary Master Plans• Looks at a reach by reach stream stability• Groups similar stream characteristics by reach
– Soils– Vegetation– Hydraulic properties
• Develops a stable channel grade:– By reach– By soil type
• Allows for an optimized placement of drop structures
Page 8
Required Data
Page 9
Revised Permissible Velocity Methodology
• 3 “Typical Sections” selected– normal depth assumption– no interference from hydraulic structures
• Velocity computed for cross section• Slope adjusted until permissible velocity reached • Slopes for each typical section averaged to
determine stable slope for each reach.
Page 10
Page 11
Permissible Velocity ValuesSoil Description Fortier and Scobey (1926)
Soil Types within Study Area Permissible Velocities (fps)
NRCS Soil Type Applied
NRCS Soil Description
USCSClear Water*
Water Transporting Colloidal Silt*
Flow Depth3 to 5 feet**
Flow Depth 5 to 8 feet**
Flow Depth 8 to 10 feet**
Grass Lined ***
Ordinary Firm Loam
BrD, Bte, BrB Cre, NeE
Bresser, Bresser Truckton, Crawfoot Tomah, and Newlin Sandy Loams
SC-SM 1.7 - 2.5 2.7 - 3.5 3.9 4.6 4.9 6.8
Stiff ClayKuD, Jb, Fu, CP, FoD
Kutch Clay Loam, Jarre Brusset and Fondis Kutch Association, Fondis Clay Loam and Pits Clay
CL 3.4 5.0 5.3 5.5 6.0 6.8
Alluvial SiltLo, Lu, SE, Sd, Se, St
Loamy Alluvial Land, Sandy wet Alluvial Land, and Sampson Loam
CL 2.0 - 3.8 3.5 - 5 3.9 4.6 4.9 6.8
Sandy LoamPpE, PrE2, KtE
Peyton Pring Crowfoot and Kutch Sandy Loams and Complex
SC 1.75 - 2.0 2.5 - 3.5 3.9 4.6 4.9 6.8
Graded Loam to Cobbles
Hg, GP, SuHilly gravelly land and pits gravel and Stony rough land
SC 3.8 5.0 5.3 5.5 6.0 6.8
* Fortier and Scobey (1926)** Known et all (1977)*** SCS (1954) and UDFCD (2006)
Page 12
Revised Permissible Velocity Results
Tributary Reaches Soil TypeStable Slope
(ft/ft)
Omni 1,2 Alluvial Silt, Firm Loams 0.004
Omni 3,4,5 Firm Loams 0.010
Omni 6 Sandy Loams, Clay 0.015
Tributary to Omni 1,2 Clay, Firm Loams, Sandy Loams 0.013
Industrial 1,2,3 Firm Loams 0.004
Industrial 4,5,IT1 Firm Loams, Sandy Loams, Gravel 0.018
Westfield 1 Firms Loams, Silt 0.006
Westfield 2,3 Firm Loams 0.012
Westfield 4 Clay, Sandy Loams 0.041
Tributary Reaches Soil TypeStable
Slope (ft/ft)
North Dawson 1,2,3 Alluvial Silt, Firm Loams 0.004
South Dawson 1,2,3,4,5 Firm Loams 0.007
South Dawson 6.7 Stiff Clay, Firm Loams, Sandy Loams 0.020
Page 13
Revised Permissible Velocity Results
Soil TypeMinimum Slope
ft/ftMaximum Slope
Ft/ft
Alluvial Silt 0.004 0.006
Firm Loams 0.004 0.02
Sandy Loams 0.013 0.041
Clay 0.013 0.041
Gravel 0.018 0.018
Page 14
Revised Permissible Velocity Reality Check
y = 0.2622x-0.6837
R2 = 0.5566
0.00000
0.00500
0.01000
0.01500
0.02000
0.02500
0.03000
0.03500
0.04000
0 200 400 600 800 1000 1200 1400 1600 1800
Q (cfs)
s (f
t/ft
)
Page 15
Case Studies
• Applies revised methodology to past studies to quantify optimized drop structure cost savings over traditional methods
• 3 Case Studies– 6400 Tributary
• Used Stable Slope of 0.4% by Permissible Velocity approach
– Scott Gulch• Used Stable Slope of 0.4% by Recommendations
– Lemon Gulch• Used Stable Slope of 0.4% by Recommendations
Page 16
6400 Tributary Master Plan Results
Stream ReachExisting
Slope ft/ft Soil TypeMaster Plan
Slope ft/ftRequired
Drops
6400 South Tributary Reach 1 0.028 Newlin Gravely Sandy Loam 0.004 9
6400 South Tributary Reach 2 0.039 Englewood Clay Loam 0.004 0
6400 South Tributary Reach 3 0.056 Bresser Sandy Loam 0.004 12
6400 South Tributary Reach 4 0.050 Loamy Alluvial Land 0.004 7
6400 South Tributary Reach 5 0.059 Fondis-Kutch Association 0.004 0
6400 East Tributary Reach 1 0.033 Loamy Alluvial Land 0.004 2
6400 East Tributary Reach 2 0.036 Loamy Alluvial Land 0.004 2
6400 East Tributary Reach 3 0.029 Loamy Alluvial Land 0.004 0
6400 East Tributary Reach 4 0.058 Loamy Alluvial Land 0.004 6
6400 East Tributary Reach 5 0.053 Loamy Alluvial Land 0.004 0
6400 East Tributary Reach 6 0.059 Fondis-Kutch Association 0.004 9
6400 East Tributary Reach 7 0.049 Stony Rough Land 0.004 0
6400 West Tributary Reach 1 0.037 Loamy Alluvial Land 0.004 4
6400 West Tributary Reach 2 0.041 Loamy Alluvial Land 0.004 13
6400 West Tributary Reach 3 0.053 Renohill-Manzanola Clay Loams 0.004 9
6400 West Tributary Reach 4 0.041 Stony Rough Land 0.004 0
Page 17
6400 Tributary Revised Permissible Velocity
Stream Reach Existing Slope ft/ft Soil TypePermissible Velocity
Slope ft/ftRequired
Drops
6400 South Tributary Reach 1 0.028 Newlin Gravely Sandy Loam 0.004 9
6400 South Tributary Reach 2 0.039 Englewood Clay Loam 0.006 0
6400 South Tributary Reach 3 0.056 Bresser Sandy Loam 0.005 11
6400 South Tributary Reach 4 0.050 Loamy Alluvial Land 0.009 5
6400 South Tributary Reach 5 0.059 Fondis-Kutch Association 0.02 0
6400 East Tributary Reach 1 0.033 Loamy Alluvial Land 0.004 2
6400 East Tributary Reach 2 0.036 Loamy Alluvial Land 0.005 1
6400 East Tributary Reach 3 0.029 Loamy Alluvial Land 0.005 0
6400 East Tributary Reach 4 0.058 Loamy Alluvial Land 0.005 5
6400 East Tributary Reach 5 0.053 Loamy Alluvial Land 0.007 0
6400 East Tributary Reach 6 0.059 Fondis-Kutch Association 0.037 5
6400 East Tributary Reach 7 0.049 Stony Rough Land 0.05 0
6400 West Tributary Reach 1 0.037 Loamy Alluvial Land 0.007 2
6400 West Tributary Reach 2 0.041 Loamy Alluvial Land 0.009 11
6400 West Tributary Reach 3 0.053Renohill-Manzanola Clay
Loams 0.053 0
6400 West Tributary Reach 4 0.041 Stony Rough Land 0.041 0
Page 18
6400 Tributary Results Comparison
• Master plan required drops– 73
• Revised permissible velocity required drops– 51
• Drop savings– 22
• Cost Savings– $1,650,000
Page 19
Implementation Philosophy
• Priority 1 Improvements :– To protect critical structures and private property;– Necessary now to mitigate damage to existing flood
control facilities and environmentally sensitive areas;– and at locations with active head cutting or streambed
erosion.
Page 20
Implementation Philosophy
• Priority 2 Improvements: – Required as development or significant changes to the
watershed occur;– located to bring stream thalwag to approximately 80%
of calculated stable slope.
Page 21
Implementation Philosophy
• Priority 3 Improvements– Required if streams exhibit degradation after
implementing priority 1 and 2 improvements;– to protect structures if conditions warrant; – if major changes in the watershed occur that were not
originally considered.
Page 22
Prioritizing Improvements
• Based on field observations– Localized areas of instability– Damage to existing infrastructure
• Based on stream stability analysis– Used to determine stable channel grade– Used to place proposed drop structures
• Based hydraulic analysis– Used to check existing conveyance– Used to size future infrastructure
Page 23
Phased Cost Approach
• Total Cost of all improvements for Omni Trib.– $6,935,800
• Total Cost of Priority 1 Improvements– $2,019,700
• Priority 1 Improvements are 29% of total cost• Total Cost with Priority 2 Improvements
– $4,839,900• 80% of the stream stabilized with Priority 1 and
Priority 2 Improvements– 70% of the total cost expenditure
• May never need to implement priority 3 improvements
Page 24
Conclusion
• Cost savings of modified permissible velocity stream stability analysis– Quick and cost effective with a minimum of required
data– Allows for a varied slope to optimize required drop
placement• Cost savings of phased approach for
improvement implementation– Allows for implementation from multiple stakeholders– Identifies structures key to public safety and health– Allows for a long term phased approach to stream
improvement
Page 25
Questions?