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

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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

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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

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Required Data

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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.

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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)

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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

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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

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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

)

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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

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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

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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

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6400 Tributary Results Comparison

• Master plan required drops– 73

• Revised permissible velocity required drops– 51

• Drop savings– 22

• Cost Savings– $1,650,000

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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.

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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.

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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.

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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

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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

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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

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Questions?