geomorphic assessments of major city of austin … · eric stewart, p.e., cfm, env sp (hdr) cris...

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Morgan Byars, P.E., (City of Austin)

Eric Stewart, P.E., CFM, ENV SP (HDR)

Cris Parker, P.E., CFM (HDR)

September 4, 2014

G E O M O R P H I C

AS S E S S M E N T S O F M AJ O R

C I T Y O F AU S T I N

WAT E R S H E D S

M I SS I O N – C I T Y O F AU ST I N

WAT E R S H E D PR O T EC T I O N D EPAR T M EN T

» Reduce the impact of flooding, erosion and storm water pollution on our

community in order to protect lives, property and the environment.

» Mission Integration Program (MIP)

» Water Quality

» Creek Erosion - Stream Restoration Program

» Flood Control

» Purpose - Maximize the opportunities and

minimize negative impacts

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ST R E AM R ESTO R AT I O N PR O G R AM

» Problem Assessment

• Site Specific, Reach-based, Watershed Scale

» Project Delivery

• Planning and Prioritization

• In-house and Capital Improvements

» Regulatory Criteria

• Erosion Hazard Zone

• Open Channel Design Criteria

• Standards

» Field Engineering

• Maintenance Crews

» SRP Design ~4,000 linear feet of stream/year

• Scour protection

• Stream Stabilization

• Stream Rehabilitation

• Stream Restoration

WAT E R S H E D PL AN N I N G -

ER O SI O N

» Asset Management (Creeks)

• Inventory

• Condition Assessment

• Erosion Hazards

» 1997 – City-wide Watershed Erosion

Assessments

• 17 watersheds (urban)

» 2002 Onion Creek, 2006 Carson Creek

» 2012 – Erosion and Geomorphic

Assessments

• 6 watersheds (suburban)

• Outside city limits, but within

desired development zone

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PL AN N I N G AN D PR I O R I T I Z AT I O N

» Erosion Mission Problem

Score Approach

• Erosion Site Score

• Reach Score

» City-Wide Erosion Database

• Erosion Sites

» Site Severity

» Threatened Resource

» Physical Characteristics

• Geomorphic Reaches

» Stability Rating

» Visual and Quantitative

ER O SI O N PR O B L EM PR I O R I T I Z AT I O N

» Erosion Problem Score

• ECscore = ESseverity * Resource Value

• ES = f(Geotechnical + Planform + Surface Cover)

» Geotechnical = f(bank height, bank angle, resource distance, soils)

H existing

Resource

Critical

Slope

Toe of Bank

Top of Bank

Threatened

Resource

b

Offset

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G EO M O R PH I C AS S E S SM E N T S - O B J EC T I V E S

» Map and Characterize

• Stream Reaches

• Erosion sites

• Threatened resources

» Delineate erosion hazard zones

» Prioritize sites and reaches

G EO M O R PH I C AS S E S SM E N T S – STAT U S

» Recently completed six watersheds

• Gilleland

• Harris Branch

• Decker

• Elm

• Slaughter

• South Boggy

» 112 square miles

» 210 miles of stream

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SC O PE

» Phase 1

• Desktop planning

• GIS

• Delineate geomorphic like reaches

(GLRs)

• Refine scope

• Accessibility determination

» Phase 2

• Stream reconnaissance and survey

• Analysis

• Mapping

• Report

SC O PE

» Phase 1

• Desktop planning

• GIS

• Delineate geomorphic like reaches

(GLRs)

• Refine scope

• Accessibility determination

» Phase 2

• Stream reconnaissance and survey

• Analysis

• Mapping

• Report

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EASTERN WATERSHEDS

ST R E AM T Y PES

EASTERN WATERSHEDS

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» GPS (handheld)

» Field photos

» Reach Morphology

» Bed Morphology

» Bank Morphology

» Manmade Structures

» Survey Cross Sections

ST R E AM R EC O N N A I S S A N C E

R E AC H M O R PH O L O G Y

» Planform

» Stability

» Meander Belt

» Floodplain

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» Bed material type

» Morphology

» Bed forms

» Armoring

» Knickzones and

headcuts

B ED M O R PH O L O G Y

» Left and right

» Protection

» Bank Material

» Bank Stability

» Bank Vegetation

B AN K M O R PH O L O G Y

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» Grade control

» Channel spanning

» Outfalls

» Bank Revetments

M AN M AD E ST R U C T U R E S

» Rapid stability assessment

» Survey and monument

» Historical utility crossings

STAB I L I T Y

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» Erosion Site Inspection

» Localized Reach Based

Erosion Prioritization

STAB I L I T Y

» Erosion Site Inspection

» Localized Reach Based

Erosion Prioritization

STAB I L I T Y

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Q U I C K R EF ER E N C E

SU M M ARY

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EASTERN WATERSHEDS

ER O SI O N H AZ A R D Z O N ES

» An area where stream channel erosion is likely to result in damage to or

loss of property, buildings, infrastructure, utilities or other valued

resources.

» Applies to areas with minimum drainage area of 64 acres

» Comparison to existing local regulatory development zones

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C I T Y O F AU ST I N O B SERV E D I N C I S I O N D EPT H S


Category 1

Category 2

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» Mostly within existing regulatory

areas like floodplain or Critical

Water Quality Zone

» Not a buffer, but area that needs

special attention

» Guidance in the Drainage

Criteria Manual

» Provisions in the Watershed

Protection Ordinance

SOUTHWESTERN WATERSHEDS

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SLAUGHTER AND SOUTH BOGGY CREEK

31 Sq. Mi.

62 Stream Miles

SLA5 Sq. Mi.

10 Stream Miles

SBG

31 Sq. Mi.

62 Stream Miles

SLA5 Sq. Mi.

10 Stream Miles

SBG

ST R E AM T Y PES


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H I STO R I C A L L AN D U SE & L AN D C O VER - 1 9 8 4


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ER O SI O N S I T ES


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F I N D I N G S

» Eastern Watersheds

» Largely undeveloped compared to

SW watersheds

» Instabilities associated with

grazing, agriculture, and loss of

riparian buffer

F I N D I N G S

» South Boggy Creek

» Developed prior to watershed

protection rules

» Less stormwater controls

» More problem areas

compared to Slaughter Creek

» Channel enlargement

» Meander migration

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F I N D I N G S

» Slaughter Creek

» Mostly developed within last

25 years post-watershed

protection

» WQ setbacks

» 100-yr detention

» Structural WQ controls

» Less problem areas observed

W H Y AL L T H E EF F O R T ?

» Drainage Utility Asset Management

» Informed decision making

• Identification and prioritization of WPD projects

• Advise management strategies - preservation, restoration, rehabilitation,

stabilization

• Erosion hazard information for creek side development

» Easily accessed data for public inquiries

» Institutional knowledge from getting “feet wet”

» Effort is scalable. Little effort goes a long way.

» Future studies

• e.g. Monitor monumented cross sections, study of enlargement ratios

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Q U EST I O N S AN D AN SW E R S

Morgan Byars

City of Austin

[email protected]

512-974-9790

Eric Stewart

HDR

[email protected]

512-912-5115

mailto:[email protected]

mailto:[email protected]

geomorphic assessments of major city of austin … · eric stewart, p.e., cfm, env sp (hdr) cris...

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