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

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

These are structures Use caution Understand the processes at work in the system Know the components of a check dam !

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

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.

The stream or gulley will start by attacking the bottom of the channel first.

The channel will get deeper Section

The channel will keep getting deeper until the sides start to fall in Section

Then it starts to get wider Now it is really starting to get bad

This is process is called the channel stages Stage 1 Section Stage 3 Stage 2 Assessment Tool: Channel Stages Good for collection and transport zone

STAGE 1 Test Time

Headcut STAGE 2 Channel downcutting creates straighter, steeper gully.

widening STAGE 3 Channel widening, cut banks on both sides.

It is best to stop this process early in Stage 2

To stop it: use a check dam Profile Stage 2

Profile 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 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. Made worse by bad bank key

Question: What is wrong with this check dam? Answer: bank key in

Answer: everything, bad spacing, no control section, no bed or bank key in, no energy dissipation Question: What is wrong with this check dam?

Answer: nothing major

Question: What is wrong with this check dam? Answer: nothing major

Question: What is wrong with these check dams? Answer: nothing major

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

The End