The Mission Reach Ecosystem Restoration Project: Floodplain Management Within a Multi-Objective Project Paradigm Steven Schauer San Antonio River Authority Tim Whitefield, P.E., CFM Jacobs Engineering Group Inc. May 24, 2012

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 REACH ECOSYSTEM 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 Flow 2-Year100-Year U/S of San Pedro D/S of San Pedro Year Effective Flow 100-Year

Design of Pilot Channel

Use riffle structures to establish "effective slope", also provide grade control Effective Slope = Channel Slope =

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” –Zone “D” – –Zone “E” – 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! Restoration Hydraulics vs WHAT CRITERIA TO USE WHILE APPLYING VARIOUS DENSITIES?

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 Tim Whitefield, P.E., CFM Jacobs Hydraulic Engineer