Date: 03/05/2009
Water Diversion- Field Site
Curriculum
Primary Author:
Robert Hedburg, CF®
St. Louis Co. Land Depart.
hedburgb@co.st-louis.mn.us
(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/accessroa
ds.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)