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HYDRO20750
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HYDRO20750
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Last modified
8/24/2016 8:41:59 PM
Creation date
11/20/2007 1:44:04 PM
Metadata
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Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
Hydrology
Doc Date
7/5/2005
Doc Name
Evaluating the Effectiveness of Postfire Rehabilitation Treatments
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MCC
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DMG
Permit Index Doc Type
Correspondence
Media Type
D
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installed or put in locations where they can not contain <br />runoff. Straw bale check dams are considered by many <br />BAER project coordinators to be effective emergency <br />rehabilitation treatments. Straw bale check dame <br />appear to work better than contoured felled loge. Some <br />Forests use straw bales below culverts to disperse flow <br />and trap sediments. They appear to the moat aucceas- <br />ful in channels small enough to require only three <br />bales, but in narrow, steep drainages two-bale wide <br />structures do not function as well. <br />Others do not recommend use of atrawbalea because <br />they fill to capacity after small storms. They can be <br />washed out later even when anchored with "U" shaped <br />1/8 in (3 mm) re-bar are useful only in the upper <br />reaches of watersheds (let or 2nd order drainages) <br />that are often difficult to access, and can be easily <br />undercut ifenergy diasipatora are not installed. One of <br />the comments on straw bale check dame was there is <br />always a risk of failure in large events. These dams <br />cannot be designed for large storms, and will fail <br />during significant runoff events. <br />Implementatron and Environmental Factors. A large <br />number of comments were made about important <br />implementation and environmental factors that affect <br />the success of straw bale check dame. Regarding <br />implementation, akey factor is having a skilled imple- <br />mentation leader and trained, experienced crews. <br />Straw bale check dams are costly and labor intensive. <br />With such a high investment, the dame must be well- <br />designed, properly placed, and well built. <br />Generally speaking, straw bales work beet in drier <br />regions, on small drainage areas that have low gradi- <br />ents (less than 30 percent), and in channels that are <br />not incised. The bales need to be placed so that they <br />contact the channel bottom, are curved up to and <br />keyed into banks, and are adequately staked or wired <br />to stay in place. Inter-bale spaces need to be filed ao <br />that channelized flow does not occur. "LT" shaped re-bar <br />seems to work well in stabilizing bales but don't <br />guarantee thatthebalea will remainin place. Geotextile <br />fabric works well ae an energy diaeipator and should <br />be placed starting on the uphill side *~+*+ni*+g over the <br />bales in the center of the channel and downstream in <br />a splash pad. Chicken wire and staking should be used <br />to keep the geotextile in place. Rock, wood, or other <br />straw bales can also be used as energy diasipatora but <br />must be large enough or well-anchored to prevent <br />movement during runoff. Straw bale check dams seem <br />to work better and survive longer than silt fences, <br />especially when reinforced with wire on the upstream <br />aide. <br />Other Factors. Because straw balsa will break down <br />over time and fail in high flows, maintenance during <br />the first year is very important. Straw bales are not <br />readily available early in the year. After August they <br />are very available. Rice straw bales should be consid- <br />ered because they usually do not contain noxious <br />weeds, and weeds associated with rice trope do not do <br />well on dry hillalopes and ephemeral channels. Straw <br />bale check dams can be destroyed by grazing animals <br />such as cattle and elk. Bears also have a peculiar <br />tendency to indulge in ripping straw bale check dams <br />apart. <br />Grade Stabilizers <br />Purpose. The purpose of log grade stabilizers is much <br />the same as log dame, except that the emphasis is on <br />stabilizing the channel gradient rather than trapping <br />sediment. <br />Relative EFfectrveness Excellent-30% Good-30% Fair- <br />10% Poor-30% (Replies = 10) <br />Interviewees rated log grade stabilizers about equally <br />across the spectrumfrom "excellent" to "poor."Like log <br />dame, these structures are expensive and time-con- <br />suming. In aituationswhere log grade stabilizers were <br />rated "excellent," 70 to 80 percent of the structures <br />were still functional after 1 year. "Poor" ratings usu- <br />ally resulted where the log grade stabilizers did not <br />make a difference or they were lost to high stormflows. <br />LnplementatronandEnvlmmnentalFactors: Loggrade <br />stabilizers have many of the same design, implemen- <br />tation, and environmental factors considerations that <br />log dame do. Proper design and crew experience are <br />critical in making these structures last and function <br />effectively. Numerous small log grade stabilizers are <br />preferable to a few larger ones. In some locations, <br />there might not be adequate, straight, woody material <br />left after a fire to build log grade stabilizers with onsite <br />resources. <br />Rock Grade Stabilizers <br />Purpose. The purpose of rock grade stabilizers is the <br />same as log grade stabilizers, except that they are <br />made of rock. The emphasis is on stabilizing the <br />channel gradient rather than trapping sediment <br />although eome sediment will be trapped by these <br />structures. <br />Relative Effectrveness Excellent-0% Good-33% Fair- <br />67% Poor-0%a (Replies = 3) <br />Only a few interviewees commented on rock grade <br />stabilizers. They rated this technique as "good° to <br />"fair." There were not many comments about this <br />technique. <br />Implementatron and Environmental Factors Many <br />comments on implementation and environmental fac- <br />tors pertaining to log grade stabilizers, apply to rock <br />grade stabilizers. Proper design, adequate planning, <br />and experienced crews often make the difference <br />80 USDA Forest Service Gen. Tech. Rep. RMRS-GTR~3. 2000 <br />
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