the mission reach ecosystem restoration project: floodplain management within a multi-objective...

The Mission Reach Ecosystem Restoration Project:Floodplain Management Within a Multi-Objective

Project Paradigm

Steven SchauerSan Antonio River Authority

Tim Whitefield, P.E., CFMJacobs Engineering Group Inc.

May 24, 2012

CREEK

ALAZAN

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EE

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RIVER

SAN

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IO

ALAMO ST.

NUEVA ST.

HILDEBRAND AVE.

LEXIN

GTO

N AVE.

LEGEND

TRIBUTARY

HEAD WATERS

MISSIONESPADA

35

37

35

410

9090

81

81

281

281

CR

EE

K

SAN

PED

RO

APACHE

W E

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SAN JUANMISSION

SAN JOSEMISSION

CONCEPCIONMISSION

SAN ANTONIODOWNTOWN

CR

EE

K

MA

RT

INE

Z

ORIGINAL ALIGNMENTSOUTH OF DOWNTOWN

SACIP

Channelized River

San Pedro Creek Tunnel

San Antonio River Tunnel

MISSION REACH

• Partnership project between: – U.S. Army Corps of Engineers– San Antonio River Authority– Bexar County– City of San Antonio– San Antonio Water System– San Antonio River Oversight Committee– San Antonio River Foundation

MISSION REACHECOSYSTEM RESTORATION & RECREATION

PROJECT

• 23,500+ young trees & shrubs• 320 acres of riparian woodland habitat• 113 acres of aquatic habitat • 30 riffles/weirs • 13+ acres of embayment• 2 river remnants: San Juan & Espada

Restoring Habitat Features

• OBJECTIVE:– Restore aquatic ecosystem function to highly

degraded river• CONSTRAINT:

– Must maintain “zero rise” in the 100 year water surface elevation

Goal For Design Elements

• Pilot Channel – for sediment transport

• Vegetation – maintain flood capacity

• Structures and river features

Add additional functions back into the river - but maintain 100-year flood

carrying capacity

Design of Pilot Channel

• Develop understanding of existing sediment yield &

capacity

• Determine desired regime - yield & capacity

• Size pilot channel for each phase (dimensions &

slope)

Guidelines:

Design of Pilot Channel

• Pilot channel sized to carry "effective discharge"

• Hypothetical value presumed to transport most of the

sediment over time

• Flow for which frequency and sediment transport are

maximized

• Typically 1-2 year recurrence - can be more frequent

Design of Pilot Channel

 Effective

Flow2-Year 100-Year

U/S of San Pedro 1180 8292 21284

D/S of San Pedro 2320 22426 70396

2-Year

Effective Flow

100-Year

Design of Pilot Channel

Design of Pilot Channel

Design of Pilot Channel

• Use riffle structures to establish "effective slope", also provide grade control

Effective Slope = 0.0018

Channel Slope = 0.0022

Vegetation

Vegetation

• Density:– Trees will be planted in 3 densities to model

various riparian conditions:– “A” – 250 trees per acre (~13 ft. o.c.)– “C” – 70 trees per acre (~25 ft. o.c.)– “D” – 27 trees per acre (~40 ft. o.c.)– “E” – herbaceous vegetation only – no trees

Vegetation

•Manning's “n” values for project– Zone “A” – 0.15 – Zone “C” - 0.085– Zone “D” – 0.055– Zone “E” – 0.035

--Desire is for entire project to be suite "A" --Exceptions are considered "hydraulic concessions"

Vegetation

Generally, denser areas should be further from the water

Type A density represents the most natural condition overtime, and should be relatively uniform

across the channel

Generally, denser areas near the water provide higher quality habitat

Type A provides the most hydraulic resistance, and should be used sparingly

BALANCE!

RestorationHydraulics vs

WHAT CRITERIA TO USE WHILE APPLYING VARIOUS DENSITIES?

Vegetation

Vegetation

Type A

Type C

Type D Type

E

Vegetation

Type E

Type D

Type C

Type A

Structures

• 22 Riffles• 8 Weirs• 4 Pedestrian Bridges• Toe protection for erosion control• Concrete and gravel trails

River Features

•8 Embayments•2 “Run” segments•30 “Pool” segments•8 Scour Pools•2 Restored river remnants•7.5 acre “bottomland hardwood forest”•320 acres of wooded riparian corridor

What is an Embayment?

• Man-made habitat features that tend to simulate oxbows

• Shallow water adjacent to channel• Increase surface area, shoreline length• Add variation to velocity and depth• Create habitat for plants & fish

What Does it Look Like?

Questions?

Steven Schauer

San Antonio River Authority

Manager of External Communication

210-302-3644

sschauer@sara-tx.org

Tim Whitefield, P.E., CFM

Jacobs

Hydraulic Engineer

817.735.6286

tim.whitefield@jacobs.com