Project Status

1
BENTLE BRANCHStream Stability Study and Storm
Water Master Plan Update

• Project Status
• June 2005

2
Project Objective
To develop a comprehensive Stream Stability and
Storm Water Master Plan for the Bentle Branch
Watershed addressing drainage, flooding, and
erosion problems and develop a master plan to
reduce flooding and erosion impacts along Bentle
Branch.
3
Past Studies

• Flood Control Feasibility Study Of Ten Mile Creek
  Tributaries
• FEMA Flood Insurance Study

4
Background

• City of Duncanville
• July 2004 Flood
• Bentle Branch Watershed
• Project Reach

5
Stormwater Master Plan Alternatives

• Channel Alteration
• 1986 Halff Study Findings Still Apply
• Joe Wilson Road
• Detention
• Utility Crossings on Ten Mile Creek

6
Detention

• No Suitable Duncanville Detention Sites
• Regional Detention Site in Cedar Hill
• 7 Discharge Reduction Through Duncanville

7
Ten Mile Creek Utilities

• Susceptible to Debris Blockage

• Significantly Increases Backwater for Small Floods

8
City of Duncanville Utility
9
Ten Mile Creek Utilities

• XX

10
Stability Assessment
Current
Why do streams like Bentle Branch erode?
Urbanization
1995
11
Stability Assessment
Channel Evolution ? Downcutting
12
Stability Assessment
Channel Evolution ? Widening
13
Stability Assessment
Channel Evolution ? Equilibrium (balance)
14
Stability Assessment

• Bentle Branch Evolution
• Bottom Degrades About 1 Inch/Yr
• Channel Widens in the Alluvial Zone
• Increased Resistance to Erosion

Eroded Bank
Limestone
Toe of old channel
Alluvial Soils
Rockline
Limestone Banks
Limestone Bed
15
Stability Assessment
16
High Risk Structure Rankings

• Encroachment Zones Developed
• Structures Ranked

17
Erosion Control Measures

• Vegetated Geogrids
• Vegetated Geoweb Slope Protection
• Vegetated Riprap
• Vegetated Gabion Slope Protection
• Sand Cement Bag Walls
• Use Only In Areas of Low Velocity and Erosion

18
Vegetated Geogrids
Cottonwood Creek Hutchins, TX
1st Year Growth May 2002
Installed March 2001
19
Vegetated GeoWeb Protection
Kirby Creek - Roseville, CA
Note Pictures Taken From SSPCO, Inc. Website
20
Vegetated Riprap
Note Pictures Taken From Terraerosion Control
Ltd. and Augusta, North Carolina Websites
21
Vegetated Gabion Slope Protection
Old Stone Dam Allen, TX
22
Sand Cement Bag Walls
Bentle Branch - Duncanville and Cedar Hill, TX
23
Summary

• Hydrology and Hydraulic Analyses Have Been
  Completed.
• Floodplain Mapping Has Been Completed.
• Flood Control Master Plan Alternatives Have Been
  Evaluated.
• Channel Stability Assessment Has Been Completed.
• Stream Bank Stability Alternatives Are Being
  Formulated.
• Report is Underway.
• Website www.duncanvillebentle.com

24
BENTLE BRANCHStream Stability and Storm Water
Management Update

• Project Status
• June 2005