Date: 03/05/2009
Water Diversion- Field Site
Curriculum
Primary Author:
Robert Hedburg, CF®
St. Louis Co. Land Depart.
(218) 625-3700
I. Target audience(s)
Loggers, Foresters, Land managers, and Woods roads builders .
II. Learning Objective(S)/Purpose
This station will discuss water diversion and erosion control. Including the importance of managing runoff on skid trails & logging roads and how to determine the best structure for the site.
III. Presentation Outline
The presentation will consist of site examination of diversion structures:
A. Why are diversion structores necessary? Diversion strcuturesmove water off trails or roads to limit erosion which can pollute streams ,lakes, and wetlands; reduce forest productivity ; make road impassable, and just plain looks bad.
B What type of diversion structure should be used? The needs and conditions of the site will help determine what structure to use. The FMGs and handout has some guides to determine the number and recommended spacing of water diversion structures. The type of structure should determined based on the future use of the road or trail.
Season of harvest can also effect your choice. The amount of slope and soil disturbance can be important. Snow cover can help limit the amount of soil disruption.Remember that the water diverted in the upper 1/3 of the slope cuts down on 2/3's of the erosion impacts at the base of the slope. The more water and speed at the bottom of the slope means more erosion. Visual example: Hold up a bowling ball ,ask participants where on the hill they would like to stand catch (or divert) it when rolled down hill. (Please don't do it for real!!)
C. Discuss the range of options- Advantages and Disadvantages
1. Water bars
A: lower cost for material; D:should only be used on closed trails( can be pulled out or worn down by follow up users ATVs ).
2. Broad base dip (BBD)- A: low cost, can be used on open road, truck traffic is not slowed much, D: need to be built into road(engineered) and needs special operator skill and attention to work properly.
3. Slash, A: cheap, abundant, acts as a barrier to deter ATV and 4x4 use, D: difficult to get good continuous contact with surface to divert flow.
4. Chip mulch, A: cheap, can be use to cover landing, D: requires chipper, difficult to transport to trails away from landing, less effective on steeper slopes.
5. Open top box culvert,A: lower cost , simple to build, will intercept over surface flow. D: needs to be maintained by cleaning to remove sediment and trash, makes grading surface difficult.
6. Metal culvert, A: quicker to install with small backhoe or excavator, easier to grade over. D: Can be costly ($3.50 to $7.00 per foot), can freeze and plug, can be harder to clean out, ends need protection markers and rip-rap
7. Silt fence, A: easy to place over uneven surfaces, commonly available, D: doesn't stop all water flow, D: needs to be “dug in”, easily knocked down or run over by ATVs or other vehicles, stakes make great firewood, fencing degrades in sunlight over time (1-2 years)
8. Wattles (stick bundle or straw), A: straw type will form over uneven surface, stick bundle will hold soil back fill, D: not readily available, straw wattles are bulky to move, stick bundles are time consuming to make on site
9. Conveyor belt, A: will easily allow vehicle passage, doesn't require special road shaping like BBD, can be easily constructed, can be graded over with caution. D: needs to be set by hand tools, used conveyor belting may be hard to find
10. Straw(hay) bales, A: commonly available, can be formed to uneven surface, will swell when wet to block most flow, D: can be a source of non-native invasive plant species, bulky to move, must be staked in place (2 per).
11. Various types of matting. A: quick and good soil holding properties, D: Expensive & bulky for amount of coverage, not effective for water diversion. Limited use because of cost, use on steep slopes with highly erodible soils.
12. Burlap and saw dust berm, A: good potential for winter application, roll of burlap is easy transport, sawdust usually available on site. will form over uneven surface and settle after spring thaw. D: may have difficulty fastening down on frozen or snow packed surface, may not divert all water, must be placed by hand, could be disturbed by following users.
D. What could happen if you do nothing?
You may have no problem. The site could receive a gentle sprinkling of rain and new plants may cover the site with little or no erosion for the entire growing season. This is very unlikely.
Remember to be careful. If you ignore it, with normal rain or runoff and a stream, lake or wetland is silted and polluted, a $10,000 fine from the MPCA is not uncommon; perhaps up to six figures for flagrant violations. You would also have to fix it and that that could be more costly than the fine.
IV. Discussion Questions
How can you minimizeon the need for erosion control and water diversion structures?
a. the importance of proper initial road and trail layout. Follow slope and contours.
b. Season of entry- Site timing
Road or skid trail closure/ re-vegetation what to use/avoid.
V. Frequently Asked Questions
Q:What is the best means of water diversion or erosion control for my site?
A: That will vary. The real question is “What is the best and most reasonable for my site? You need to review you range of solutions and the limits of the site. Is it on public or private land? Will the road or trail stay open?
Q:Are these the only option I can use?
A: Not necessarily, These are the most common options that have shown to be effective. There may be other materials and options possible, yet to be developed. You may have ideas that can be implemented to solve a problem or create new technique.
Q: What if I install everything according to the book and there is a problem? A: The treatments presented are for “normal” conditions. Most of the time rain or spring runoff will be easily handled by simple water diversion measures. You can't build for every possible storm, but you will soften the blow of the “gully washers”.
There could be problems because of the actions other individuals (e.g. someone removes a water bar).
Q: Is there any special treatments to consider when harvesting biomass?
A: Yes, the coarse residue that is left in a conventional operation will likely be less across the site. The flow of water to trails and road could be increased. You may need to increase the frequency diversion structures to handle increased flow. This also would point to a need for even dispersal of remaining material. You may also need to “reserve” material to use for structures( water bars, chip mulch mats,etc.).It would could toward reserved
VI. Group Activity / Case Studies
Use of “grade meter” , measuring tape , and water diversion guides (FMG) to determine where and what type of water diversion to use on demo site.
1. Resources
“A Landowner's Guide to Building http://www.na.fs.fed.us/spfo/pubs/stewardship/accessroads/accessroads.htm
This has several good examples for road building and trail location.
VII. Handouts
Diagrams of structures- copy of images from FMG and elsewhere.
Site history – season of harvest, future use of site, public/private, list of products with costs, measuring equipment, etc.
VIII. Facility, field site or other presentation needs
Site should be on newly harvested logging area with sloping terrain with skid trails or roads on hillsides. Have examples structures and products available.
1. Other
“Grade meter” with guides (prototype needed)