Leon Creek Watershed Master Plan

Leon Springs Business Association

September 15, 2011

Agenda• Historic Floods• BRWM Partnership• BRWM Website• Leon Creek Watershed Master Plan• Leon Creek USACE Feasibility Study

Flood of 1921

SAR - Pecan St. Bridge

1998 Floodvement Projects

Leon Creek - IH10 near Camp Bullis & La Cantera Rd.

Olmos Creek - Hwy 281/Basse Rd & Olmos Basin Golf Course

2002 Flood

Need for Partnership• Flooding knows no boundaries• Sharing of resources• Project vetting process

Bexar Regional Watershed Management

• Interlocal Agreement (ILA) established a partnership for watershed management between:• Bexar County (County)• City of San Antonio (COSA) • San Antonio River Authority (SARA)• 20 Suburban Cities

BRWM Objectives

• Flood Control• Storm Water Management• Water Quality

• DFIRM website– DFIRM floodplains– Aerial imagery–NFIP information

• Website will be regularly updated

BRWM websitewww.bexarfloodfacts.org

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Leon Springs DFIRM

Leon Creek Watershed Master Plan

This project will deliver a Holistic Watershed Master Plan for the Leon Creek watershed

• Flood control projects• Water quality – qualitative analysis• Alternative development techniques

• Phase 1 - Regional Detention Projects• Phase 2 - Natural Water Way Conveyance Projects• Phase 3 - Combinations of Phase 1 and Phase 2

projects

Leon Creek Watershed Master Plan

• Leon Creek Watershed–Western Bexar

County– Area: 237 sqmi– Approximately

1,500 buildings in the 100-year floodplain

Damage Density Map

Watershed Annual Flood Damages

• Leon Creek: $3,064,000• San Antonio River: $7,703,000• Salado Creek: $4,721,500

Note: Damage calculation includes 10-yr, 50-yr, 100-yr, 100-yr FC, and 500-yr storm events

• Phase 1 (April 2008 – December 2008)– RSWFs– Stream/roadway crossing analysis

Leon Creek Watershed Master Plan

• 14 projects

• Total Cost: $275.6 million

• Phase 2 (April 2009 – April 2010) – NWWC Projects– Transportation

Corridor & Utility Crossings

– Stream Scour Analysis

– Alternative Development Techniques White Paper

Leon Creek Watershed Master Plan

• 21 projects• Total Cost: $147.8 million

• Phase 3 (May 2010 – January 2011)– RSWF & NWWC Project combinations– LIDs, BMPs, NCD,

Riparian/conservation buffers– Qualitative Water Quality assessment

Leon Creek Watershed Master Plan

• Phase 3– Non-structural

options evaluation:• Quantified flood

mitigation of BMPs• Recommendation:

future development with BMPs to reduce hydrologic impact and drainage infrastructure expense

Leon Creek Watershed Master Plan

http://imnh.isu.edu

• Phase 3 BMP & LID Modeling Results

Leon Creek Watershed Master Plan

• Rain barrels, rain gardens• Green roofs, pervious pvmt.• Conservation development1

• Cisterns, green roofs• Conservation development2

• Bioretention and pavement

1. Non-infiltration BMPs over karst regions (e.g. rainwater harvesting, green roofs)2. Infiltration BMPs (e.g. bioretention, rain gardens, pervious pavement)

Bioretention/Rain Gardens

http://www.beautifulleafgardens.com/garden_design

Office Building Rain Garden in Minnesota

Rain Water Harvesting

http://www.gulfcoastrenewableresources.com/rainwater_harvesting

WaterHarvest Slimline Tank

Permeable Pavements

http://www.casfm.org/stormwater_committee/MBP-02.htm

Modular Block Pavement - 1335 Elati St Denver, COPhoto Courtesty of Wenk Associates

Conservation Development

http://www.upstateforever.org/programs_comDes.html

Cluster Development minimizes impervious cover and promotes open or green space.

Traditional Development Cluster Development

LCWMP – Phase 3 Cost Estimates

Total cost : $140 million

LCWMP – Phase 3 Cost Estimates

Impacts of Implementing All Recommended Projects

• Flood Damage Reduction– $1,165,300

• Total Construction Cost– $140,000,000

• Flood Reduction Ratio– 0.26

Next Steps for SARA

• Detailed Water Quality Modeling– Identification of Low Impact Development

projects– Identification of BMPs

• Stream Preservation, Rehabilitation, and Restoration projects

• DFIRM map maintenance – FEMA LOMR Delegation for SARA

• Inclusion of Sustainability Practices using TBL approach

Contacts – Watershed Management

Russell Persyn, PE, PhD, CFMManager(210) 302-3615rpersyn@sara-tx.org

Rafael Arias Jr., PE, CFMEngineer(210) 302-3650rarias@sara-tx.org

Yolanda McGinnisAdmin. Assistant(210) 302-3630yolandam@sara-tx.org

Questions?

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