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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60

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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42

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46

48

50

52

54

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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