Introduction to Check Dams

1
Introduction to Check Dams
8
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.
2

• Check Dams
• Usually Used in Collection Zone
• Can Also be used in Transport Zone

3
These are structures

• Use caution
• Understand the processes at work in the system
• Know the components of a check dam

4
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
5
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.
6
The stream or gulley will start by attacking the
bottom of the channel first.
7
The channel will get deeper
Section
8
(No Transcript)
9
The channel will keep getting deeper until the
sides start to fall in
Section
10
Then it starts to get wider
Now it is really starting to get bad
11
This is process is called the channel stages
Assessment Tool Channel Stages Good for
collection and transport zone
Section
12
Test Time
STAGE 1
13
Headcut
STAGE 2
Channel downcutting creates straighter, steeper
gully.
14
STAGE 3
widening
Channel widening, cut banks on both sides.
15
It is best to stop this process early in Stage 2
16
To stop it use a check dam
Stage 2
Profile
17
A check dam will keep the channel from getting
too deep
Profile
18
Check Dams Lots of different types Lots of
different materials
19
A Check Dam must
Components of a check dam

• Have a Control Section
• Have a Energy Dissipation Section
• Be Keyed into Channel Bottom
• Be Keyed into Channel Bank
• Be appropriately spaced

This introduction is going to cover the
basics You may want to get more detailed training
20
Control Section Keeps the water in the channel
Bank Key Keeps water from eroding around check
dam
21

• Control Section should have the same area as a
  stable section of the stream or gully.

22
Energy dissipation section should be two times
the structure heightMaximum height should be
less than 1.5 m
H
2H
23
Key into channel bottom for a minimum of 60
cmKey into channel bank for a minimum of 1
mTop of check dam should be at least 30 cm
below top of channel
1 m
60 cm
24
Energy Dissipation Section Absorbs energy as
water flows over top.
Key into Channel Bottom Keeps water from eroding
under check dam
Same rules for all types of check dams
Profile
25
The check dams work as a teamDownstream erosion
might undermine the upstream check dam
Profile
26
Space so that the slope can be level between the
check dams and the upstream one will not be
undermined.
Profile
27
Test Time
Question What is wrong with this check dam
Answer bank key and adjacent protection
28
Question What is wrong with this check dam?
Answer no control section. Made worse by bad
bank key
29
Question What is wrong with this check dam?
Answer bank key in
30
Question What is wrong with this check dam?
Answer everything, bad spacing, no control
section, no bed or bank key in, no energy
dissipation
31
Question What is wrong with this check dam?
Answer nothing major
32
Question What is wrong with this check dam?
Answer nothing major
33
Question What is wrong with these check dams?
Answer nothing major
34
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

35
The End