the mission reach ecosystem restoration project: floodplain management within a multi-objective...
TRANSCRIPT
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
CR
EE
K
RIVER
SAN
AN
TON
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
S
N
10
10
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
Tim Whitefield, P.E., CFM
Jacobs
Hydraulic Engineer
817.735.6286