13 check dams 2006
DESCRIPTION
check damsTRANSCRIPT
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This training was prepared by the U.S. Department of Agriculture (USDA) team of Otto Gonzalez-USDA Foreign Agricultural Service (Team Leader), Jon Fripp (Civil Engineer) and Chris Hoag (Wetland Plant Ecologist)-USDA Natural Resources Conservation Service (Civil Engineers). Fripp and Hoag were the primary authors of this material. The U.S. AID provided funding support for the USDA team.
8
Introduction to Check Dams
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Check Dams•Usually Used in Collection Zone•Can Also be used in Transport Zone
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These are structures
• Use caution
• Understand the processes at work in the system
• Know the components of a check dam
!
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What happens in if all the vegetation is removed from a watershed?
Understand the processes at work in the system
Answer:More erosion of surface
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So what happens if you have more water running down the watershed collection zone?
Answer: Erosion. Gullies will form and grow. The channel will get hungry and eat its boundary.
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The stream or gulley will start by attacking the bottom of the channel first.
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The channel will get deeper
Section
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The channel will keep getting deeper until the sides start to fall in
Section
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Then it starts to get wider
Now it is really starting to get bad
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This is process is called the channel stages
Stage 1
Section
Stage 3
Stage 2
Assessment Tool: Channel StagesGood for collection and transport zone
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STAGE 1
Test Time
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Headcut
STAGE 2
Channel downcutting creates straighter, steeper gully.
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wideningSTAGE 3
Channel widening, cut banks on both sides.
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It is best to stop this process early in Stage 2
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To stop it: use a check dam
Profile
Stage 2
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Profile
A check dam will keep the channel from getting too deep
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Check DamsLots of different types
Lots of different materials
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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 basicsYou may want to get more detailed training
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Control Section: Keeps the water in the channel
Bank Key: Keeps water from eroding around check dam
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•Control Section should have the same area as a stable section of the stream or gully.
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Energy dissipation section should be two times the structure height
Maximum height should be less than 1.5 m
H
2H
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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
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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
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Profile
The check dams work as a team
Downstream erosion might undermine the upstream check dam
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Space so that the slope can be level between the check dams and the upstream one will not be undermined.
Profile
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Test Time
Question: What is wrong with this check dam
Answer: bank key and adjacent protection
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Question: What is wrong with this check dam?
Answer: no control section. Made worse by bad bank key
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Question: What is wrong with this check dam?
Answer: bank key in
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Answer: everything, bad spacing, no control section, no bed or bank key in, no energy dissipation
Question: What is wrong with this check dam?
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Question: What is wrong with this check dam? Answer: nothing major
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Question: What is wrong with this check dam?
Answer: nothing major
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Question: What is wrong with these check dams?
Answer: nothing major
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You need an engineer to help with the design if:
• 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
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The End