3 Introduction to Check Dams Kabul, Afghanistan February 2011 This watershed rehabilitation and restoration training was prepared by the U.S. Department of Agriculture (USDA) team of Jon Fripp (Civil Engineer – USDA/NRCS), Melvin Westbrook (Director USDA-NRCS/IPD), Otto Gonzalez (International Agricultural Development Specialist - USDA Foreign Agricultural Service), Clark Fleege, (Nursery Manager, USDA Forest Service, and George Hernandez (Forester - USDA Forest Service), in consultation with Lief Christenson, (USA CJTF101 Water Resources Coordinator, Afghanistan). Contact Jon Fripp at [email protected]or Otto Gonzalez at [email protected]for more information on this workshop.
50
Embed
Introduction to Check Dams - University of …...3 Introduction to Check Dams Kabul, Afghanistan February 2011 This watershed rehabilitation and restoration training was prepared by
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
3
Introduction to Check Dams
Kabul, Afghanistan February 2011
This watershed rehabilitation and restoration training was prepared by the U.S. Department of Agriculture (USDA) team of Jon Fripp (Civil Engineer – USDA/NRCS), Melvin Westbrook (Director USDA-NRCS/IPD), Otto Gonzalez (International Agricultural Development Specialist - USDA Foreign Agricultural Service), Clark Fleege, (Nursery Manager, USDA Forest
Service, and George Hernandez (Forester - USDA Forest Service), in consultation with Lief Christenson, (USA CJTF101 Water Resources Coordinator, Afghanistan). Contact Jon Fripp at [email protected] or Otto Gonzalez at [email protected] for more information on this workshop.
A check dam will keep the channel from getting too deep
Check Dams Lots of different types
Lots of different materials
A Check Dam must • Have a Control Section • Have a Energy Dissipation Section • Be Keyed into Channel Bottom • Be Keyed into Channel Bank • Be appropriately spaced
Components of a check dam
This introduction is going to cover the basics You may want to get more detailed training
Control Section: Keeps the water in the channel
Bank Key: Keeps water from eroding around check dam
•Control Section should have the same area as a stable section of the stream or gully.
Energy dissipation section should be two times the structure height Maximum height should be less than 1.5 m shorter is better!
H
2H
Key into channel bottom for a minimum of 60 cm Key into channel bank for a minimum of 1 m Top of check dam should be at least 30 cm below top of channel
section
1 m
60 cm
Energy Dissipation Section: Absorbs energy as water flows over top.
Key into Channel Bottom: Keeps water from eroding under check dam
May need a filter with log check dams
Profile
Same rules for all types of check dams
Profile
The check dams work as a team Downstream erosion might undermine the upstream check dam
Space so that the slope can be level between the check dams and the upstream one will not be undermined.
Profile
Test Time
Question: What is wrong with this check dam
Answer: bank key and adjacent protection
Question: What is wrong with this check dam?
Answer: no control section.
Question: What is wrong with this check dam?
Answer: no control section. Made worse by bad bank key
Answer: everything, bad spacing, no control section, no bed or bank key in, no energy dissipation
Question: What is wrong with this check dam?
Question: What is wrong with this check dam? Answer: nothing major
Rock Ramp Largest stones are placed at crest and on downstream face of structure
Rock Chute
( ) 529.05.150 923.112 qSD =
For S < 0.1
For So less than 10%
Robinson et. al, 1998
Stone Sizing
0.10<S<0.40
( ) 529.058.050 233.012 qSD =
D50 in inches
For So between 10% and 40%
Oklahoma
Oklahoma
Chevron Weir
Figure 12.12 St. Anthony Falls (SAF) Type Drop Structure (Blaisdell, 1948)
Traditional or Rigid grade control and drop structures
Excellent design guidance is available for the design of rigid drop structures
NEH 654 14G
Be Careful!! • Especially in transport zone • Interruption of sediment flow • Upstream effects • Fish Passage • Flood Control • Dam Safety Issues • Bank Stability • Infrastructure
Example Problem: •Water backed up behind irrigation diversion •Water overtopped banks •Flanked structure •Damaged pasture land
You need an engineer to help with the design if:
• If project is in the transport zone • The river has high velocities • The river is large • The erosion is significant • The river system is unstable • There is something very important on the bank • The project will cost a lot of money • Laws state you must have an engineer