proposed novato creek bank stabilization guidelines questa engineering corp
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Proposed Novato Creek Bank Stabilization Guidelines
Questa Engineering Corp.
Urban Bank Stabilization Problems
Privately owned creekbedTypically incising bed creating retreat of bank topsAdjacent structures need to be protectedLarge mature canopy treesLong-term Geomorphic evolutionary tendencies
Guideline Development Steps
Assess Existing ConditionsConduct Hydraulic AnalysisDetermine Long Term TrendsDefine basic Creek Management ApproachesDescribe suitable bank stabilization treatmentsProvide permitting guidance for design and permitting of bank stabilization structures
Existing Geomorphic Conditions
Long Profile Analysis
The channel has down cut about as far it can go. Natural bedrock controls prohibit extensive vertical degradation
Bankfull Channel Dimensions
Reach 1 - 33’ top width; Max depth 3 feetReach 2 – 34’ top width: Max depth 3 feet
Lack of Large Woody DebrisBedload D50 – 17 mm surface; 4.8 mm subsurface
Lateral erosion will be greatest erosion pressure in the reach
Figure 5. Reach 1 Longitudinal Profile
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83460 83960 84460 84960 85460 85960 86460 86960
DISTANCE (ft)
VE
RT
ICA
L D
AT
UM
(N
GV
D 2
9)
REACH 1_DEC 2006
GRANT BRIDGE
SIMMONS BRIDGE
FEMA 1989
GRADE CONTROLS
Figure 6. Reach 2 Longitudinal Profile
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88500 89000 89500 90000 90500 91000 91500 92000 92500
DISTANCE (ft)
VE
RT
ICA
L D
AT
UM
(N
GV
D 2
9)
NOVATO BLVD BRIDGE
REACH 2 01 03 07
FEMA 1989
GRADE CONTROLS
Existing Erosion & CanopyReach 1 Reach 2
Stable 61% 76%
Eroded 26% 16%
Protected 14% 9%
# of Priority Sites
5 6
Active erosion (ft)
1,685 1,194
Average Canopy Cover
50% 71%
Existing Hydraulic Conditions
Bankfull flows are at threshold of erosive velocities (Max. 5 to 7 fps)10-year flows are above erosive velocity (Max. 9.7 to 12.1 fps)Bank erosion episodic and is likely to occur at flows greater than bankfull, at 5 to 10 year intervalsExpect projects to be developed on a 5 to 10 year cycle
Existing Conditions Summary
Channel is near stable verticallyLateral erosion may occur over the long-term The channel should managed to maintain at a minimum the average top-width and bottom width
Creek Management Approaches
Fill ApproachCut ApproachVertical Approach
Design Approach FactorsAdjacent structure setback - 20’ distancePresence of Trees larger than 12” DBH within 5’ of Top-of-bankAverage Channel Top-widthAverage Channel Mid-widthPresence of Trees larger than 48” DBH
Bank Stabilization Design Approach Flow Chart
Existing Adjacent Structure or Utility
Building Setback> 20’
Top Width is defined as the distance from top of bank to top of bank .
MidWidth is defined as the width at half the distance to top of bank from the channel thalweg
TOB = Top of Bank; DBH = diameter as base height (~4’ above ground)
Riparian tree is defined as any tree within 10 feet of existing top of bank
Adjacent structure/utility is a structure that is permitted through existing city ordinances or is more than 10 years old
Fences are not considered structures
FIGURE
15
Riparian Trees< 12”DBH
Multiple
Trees> 12” DBH
Single
Trees < 12” DBH
Top Width < 65’
Cut Solution
Mid Width > 55’
Cut Solution
Fill Solution Cut Solution
Not Within
10’ of TOB
<48” DBH
Cut Solution
Max. Feasible
Mid Width <55’
Fill Solution Vertical Solution
Mid Width <55’
Fill Solution
Yes
Multiple
Trees Not Within
10’ of TOB
>48” DBH <48” DBH
Cut Solution/
Preserve Tree
Cut Solution/
Lose Tree
Mid Width <55’
Fill Solution Vertical Solution
No
>48” DBH
Cut Solution/
Preserve Tree
Cut Solution/
Lose Tree
Top Width > 65’
Mid Width<55’ Mid Width > 55’
Trees
Within 10’ of TOB
Mid Width > 55’ Mid Width <55’
Fill Solution Cut Solution
DRAFT
Fill Solution
Mid Width > 55’
Mid Width > 55’
Within
10’ of TOB
Cut
Solution
Cut Solution
Mid Width > 55’
Fill Solution Cut Solution
Top Width > 65’
Mid Width<55’
Mid Width > 55’ Mid Width <55’
Building Setback< 20’
Vertical Solution
or
Cut Solution
Max feasible
Trees > 12” DBH
Single
Cut Solution
Max. Feasible
Approach Check
Station 83925Priority R1-2
Structures –Shed within 20’ of TOBTrees – one stump within 5’ of TOBTop Width –55’Mid Width – 46’Solution Vertical or Cut max feasible
Priority R1-3
(Station 84350)
Structures –House within 20’ of TOBTrees – multiple trees less than 12” DBH within 5’ of TOBTop Width – 45’Mid Width – 30’Solution
Bank Stabilization Design Approach Flow Chart
Existing Adjacent Structure or Utility
Building Setback> 20’
Top Width is defined as the distance from top of bank to top of bank .
MidWidth is defined as the width at half the distance to top of bank from the channel thalweg
TOB = Top of Bank; DBH = diameter as base height (~4’ above ground)
Riparian tree is defined as any tree within 10 feet of existing top of bank
Adjacent structure/utility is a structure that is permitted through existing city ordinances or is more than 10 years old
Fences are not considered structures
FIGURE
15
Riparian Trees< 12”DBH
Multiple
Trees> 12” DBH
Single
Trees < 12” DBH
Top Width < 65’
Cut Solution
Mid Width > 55’
Cut Solution
Fill Solution Cut Solution
Not Within
10’ of TOB
<48” DBH
Cut Solution
Max. Feasible
Mid Width <55’
Fill Solution Vertical Solution
Mid Width <55’
Fill Solution
Yes
Multiple
Trees Not Within
10’ of TOB
>48” DBH <48” DBH
Cut Solution/
Preserve Tree
Cut Solution/
Lose Tree
Mid Width <55’
Fill Solution Vertical Solution
No
>48” DBH
Cut Solution/
Preserve Tree
Cut Solution/
Lose Tree
Top Width > 65’
Mid Width<55’ Mid Width > 55’
Trees
Within 10’ of TOB
Mid Width > 55’ Mid Width <55’
Fill Solution Cut Solution
DRAFT
Fill Solution
Mid Width > 55’
Mid Width > 55’
Within
10’ of TOB
Cut
Solution
Cut Solution
Mid Width > 55’
Fill Solution Cut Solution
Top Width > 65’
Mid Width<55’
Mid Width > 55’ Mid Width <55’
Building Setback< 20’
Vertical Solution
or
Cut Solution
Max feasible
Trees > 12” DBH
Single
Cut Solution
Max. Feasible
Priority R2-4
(Station 91900)
Structures –within 20’ of TOBTrees – two trees greater than 12” DBH within 5’ of TOB; none greater than 48” DBHTop Width – 90’Mid Width – 40’Solution Vertical solution
Bank Stabilization Design Approach Flow Chart
Existing Adjacent Structure or Utility
Building Setback> 20’
Top Width is defined as the distance from top of bank to top of bank .
MidWidth is defined as the width at half the distance to top of bank from the channel thalweg
TOB = Top of Bank; DBH = diameter as base height (~4’ above ground)
Riparian tree is defined as any tree within 10 feet of existing top of bank
Adjacent structure/utility is a structure that is permitted through existing city ordinances or is more than 10 years old
Fences are not considered structures
FIGURE
15
Riparian Trees< 12”DBH
Multiple
Trees> 12” DBH
Single
Trees < 12” DBH
Top Width < 65’
Cut Solution
Mid Width > 55’
Cut Solution
Fill Solution Cut Solution
Not Within
10’ of TOB
<48” DBH
Cut Solution
Max. Feasible
Mid Width <55’
Fill Solution Vertical Solution
Mid Width <55’
Fill Solution
Yes
Multiple
Trees Not Within
10’ of TOB
>48” DBH <48” DBH
Cut Solution/
Preserve Tree
Cut Solution/
Lose Tree
Mid Width <55’
Fill Solution Vertical Solution
No
>48” DBH
Cut Solution/
Preserve Tree
Cut Solution/
Lose Tree
Top Width > 65’
Mid Width<55’ Mid Width > 55’
Trees
Within 10’ of TOB
Mid Width > 55’ Mid Width <55’
Fill Solution Cut Solution
DRAFT
Fill Solution
Mid Width > 55’
Mid Width > 55’
Within
10’ of TOB
Cut
Solution
Cut Solution
Mid Width > 55’
Fill Solution Cut Solution
Top Width > 65’
Mid Width<55’
Mid Width > 55’ Mid Width <55’
Building Setback< 20’
Vertical Solution
or
Cut Solution
Max feasible
Trees > 12” DBH
Single
Cut Solution
Max. Feasible
Priority R2-6
(Station 92200) Structures – none within 20’ of TOBTrees – roughly 6 trees greater than 12” DBH within 5’ of TOB; none greater than 48” DBHTop Width – 90’Mid Width – 56’Solution
Bank Stabilization Design Approach Flow Chart
Existing Adjacent Structure or Utility
Building Setback> 20’
Top Width is defined as the distance from top of bank to top of bank .
MidWidth is defined as the width at half the distance to top of bank from the channel thalweg
TOB = Top of Bank; DBH = diameter as base height (~4’ above ground)
Riparian tree is defined as any tree within 10 feet of existing top of bank
Adjacent structure/utility is a structure that is permitted through existing city ordinances or is more than 10 years old
Fences are not considered structures
FIGURE
15
Riparian Trees< 12”DBH
Multiple
Trees> 12” DBH
Single
Trees < 12” DBH
Top Width < 65’
Cut Solution
Mid Width > 55’
Cut Solution
Fill Solution Cut Solution
Not Within
10’ of TOB
<48” DBH
Cut Solution
Max. Feasible
Mid Width <55’
Fill Solution Vertical Solution
Mid Width <55’
Fill Solution
Yes
Multiple
Trees Not Within
10’ of TOB
>48” DBH <48” DBH
Cut Solution/
Preserve Tree
Cut Solution/
Lose Tree
Mid Width <55’
Fill Solution Vertical Solution
No
>48” DBH
Cut Solution/
Preserve Tree
Cut Solution/
Lose Tree
Top Width > 65’
Mid Width<55’ Mid Width > 55’
Trees
Within 10’ of TOB
Mid Width > 55’ Mid Width <55’
Fill Solution Cut Solution
DRAFT
Fill Solution
Mid Width > 55’
Mid Width > 55’
Within
10’ of TOB
Cut
Solution
Cut Solution
Mid Width > 55’
Fill Solution Cut Solution
Top Width > 65’
Mid Width<55’
Mid Width > 55’ Mid Width <55’
Building Setback< 20’
Vertical Solution
or
Cut Solution
Max feasible
Trees > 12” DBH
Single
Cut Solution
Max. Feasible
Stabilization Treatments
Rock Toe-Retaining Wall Combination X X
Stitch Piers X
Rock Slope with Live Plantings and Rootwad Deflector X X
Vegetated Earth Filled Geogrids X X X
Live crib-wall X
Modular Pre-cast Units X
Planted Rock Revetment X X
Loose Rock Revetment X X
Live Staking and Willow Wattles X X
Erosion Control Fabric Planted w. Rooted Trees/Shrubs X X
Brush Mattress X X
Fiber rolls/ fiber rock rolls/ coir erosion blankets X X X
Flow deflectors/Rock Spurs X X X
Log, Rootwad, and boulder revetments X X X
Boulder Clusters and Rock Vortex Weirs X X X
Bank Stabilization Treatments Vertical Cut Fill
Lunker Structures X X
Design Guidance AppendixDesign Goals and Design Requirements Project Permitting & Approval Process Design Steps Existing County and City Ordinances