Environmentally Sensitive Channel- and Bank-Protection Measures (2005) / Chapter Skim
Currently Skimming:
Appendix B - Greenbank Decision Support Tool User's Guide
Appendix B - Greenbank Decision Support Tool User's Guide
Pages 41-50
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 41... ...
In order to make dialog more efficient, the user is initially asked for interest in the following four categories: • Water column habitats • Benthic habitats • The riparian zone and related terrestrial habitats or water quality • Public acceptance If interest is expressed in any of the first three of these categories, queries regarding the associated attributes appear: Water column habitats: • Providing instream or overhead cover for fish and other aquatic organisms • Providing and enhancing fish rearing habitat • Providing habitat for adult fish • Creation of velocity refugia • Pool and riffle enhancement Benthic habitats: • Providing or enhancing quality stream bottom (benthic) habitat • Decreasing the amount of sediment deposition occurring within the adjacent reach and downstream reaches • Reducing the frequency of bed movement or the severity of erosion The riparian zone and related terrestrial habitats or water quality: • Riparian habitat • Water quality improvement These queries ask the user to assign a value of very important, somewhat important, or not important to each of the 10 attributes.
|
From page 42... ...
The dialog begins with Greenbank requesting the user to characterize the erosion problem at the site in question as one of the following: • Development of gullies or rills • Erosion or scour by waves or currents • Bank collapse or mass failure Development of Gullies or Rills If the user selects "development of gullies or rills," Greenbank requests the user to specify one or more of the three causes: 42 • Overbank runoff • Piping due to steady seepage • Episodic failures due to piping from sudden drawdown or return of overbank flooding to channel Erosion or Scour by Waves or Currents If the user selects "Erosion or scour," Greenbank asks the user to classify the spatial extent of the problem as either local or general. Greenbank also asks where erosion appears to be occurring: on the bed, at the bank toe, on the middle of the bank, or on the top of the bank.
|
From page 43... ...
However, simple stability checks indicate that the bank height, slope and soil type you have described should be stable. You may continue, but you may wish to use the back or restart buttons to revisit previous questions." If the user indicates the bank is alternating sand and clay layers then the following advisory message appears: "You have indicated that general bank instability is one of the primary erosion processes operating on your site.
|
From page 44... ...
You may continue, but you may wish to use the back or restart buttons to revisit previous questions." ALLUVIAL STREAM TYPE AND EROSION RISK Elements of a simple stream classification system have been incorporated into Greenbank as an additional tool for assessing the likelihood of significant site erosion. Greenbank queries the user for values of several descriptive variables (for example, flow habit, bed material, bank material, planform, location and size of bars, channel width, and so forth)
|
From page 45... ...
Does not have the track record and level of information characterizing Level I or II. No field or laboratory design or test data, no long-term monitoring or performance data, very few literature citations or case studies, no reliable cost data.
|
From page 46... ...
Values of 3.5 m/s and 2.5 m/s appear in rows corresponding to structures built with angular and rounded stone, respectively. Clearly these values depend on the size of the rock used, but these values were adopted as 46 they correspond to the largest size material commonly used for stream and river bed and bank erosion control.5 The matrix also contains a series of columns for several key reach characteristics as follows: The matrix contains columns for each of nine key variables describing reach morphology and other site characteristics.
|
From page 47... ...
No limitations No limitations TABLE B-3 Explanation of matrix scores for site description variables. The Greenbank master matrix contains a row for each erosion control technique.
|
From page 48... ...
If the ith technique does not address the kth process and it has been rated as important, EPi,k = −100. AEPi = score indicating if the ith technique may result in additional land loss due to bank shaping or erosion after con1 9∑+ + = , H SFi i k k S EE EI B EPi i k i kk i i k k = ⎡ ⎣⎢ ⎤ ⎦⎥ ⎡ ⎣⎢ ⎤ ⎦⎥ + + = = ∑ , , , 1 11 1 11∑ + +( *
|
From page 49... ...
Option 2 is provided because best practice usually involves a combination of erosion control techniques. Greenbank suggests primary techniques that address the important erosion processes and address environmental issues of interTABLE B-5 Relationship of adjusted scores to letter grades Adjusted Score Range Letter Grade > 8 8 > adjusted score > 6 B 6 > adjusted score > 4 C 4 > adjusted score > 2 D < 2 A F
|
From page 50... ...
Many of the key inputs are echoed, along with Greenbank's evaluation of the Brice alluvial stream type and erosion risk. A short description of each recommended technique sorted from highest to lowest score is provided.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.