1.0 DEFINITION
Stream Bank Protection
Stream bank protection is the process of placing material along a bank of a watercourse for the purpose of erosion control to prevent the loss of bank material and property adjacent to the banks of the watercourse.
2.0 GENERAL
| .1 | This standard was generally derived from the Watercourse Alterations Technical Guidelines of the NB Department of Environment. |
| 2.2 | The NB Department of Environment Watercourse Alteration Regulations and Guidelines will apply to all projects including Regulation 90-80 and 90-120 under the Clean Water Act as revised in 1993. |
| 2.3 | Erosion control works shall be placed along the bank of the watercourse in such a manner as will keep encroachment into the main channel, incised channels and the flood plain to a minimum. |
| 2.4 | Any construction due to the erosion control work shall be evaluated for backwater effects, increase velocity, redirection of flow and scour effects. |
| 2.5 | The foundation of erosion control works shall be designed so that there will be no embankment failures. The possible scour depth below the protective works should be evaluated. |
| 2.6 | The material used for erosion control works must not come from the bed of the watercourse and shall be clean, inorganic, non-ore-bearing and non-toxic. Necessary filter layers shall be incorporated to prevent loss of fine material. |
| 2.7 | Erosion control works should be designed to withstand water forces from buoyancy, high velocity, wave action. The forces due to ice movement must also be evaluated in the design. |
| 2.8 | Rip rap shall meet the minimum size and gradings in tables 1 and 2. The largest stone size shall be 1.5 times the D50 and the minimum thickness of rip rap shall be 2.5 times the D50. |
| 2.9 | Some materials used for stream bank protection are: Good grass/sod cover; Rip-rap; Rock filled wire baskets and/or timber cribs; Filter cloths; Concrete blocks of various shapes; Stone (sloped and graded as per design);Wood, concrete and steel linings. |
| 2.10 | Following construction a 5.0m (16 ft) riparian zone or buffer strip should be established along the watercourse banks. Cultivation and livestock access should be restricted from this area. A vegetative cover should be established with plants capable of having dense growth and fibrous roots and provide complete soil cover. |
| 2.11 | Many techniques are used for controlling erosion such as rock placement, retaining walls and jetties. In the Maritimes the most common method is a rock slope protection. For this type of erosion control, the design should be carried out using the extensive literature on the subject so the proper size(s) and slope(s) can be determined. |
3.0 Construction
| 3.1 | Before any stream bank protection project is initiated it is imperative that a watercourse alteration permit by granted by the NB Department of Environment. |
| 3.2 | Construction should be accomplished in July, August or September whenever possible and in a manner planned to keep sediment loss from the work site to a minimum. |
| 3.3 | Rip rap shall be placed on the banks with machinery capable of controlling the drop of the rock, rather than dumped over the edge of the bank. |
| 3.4 | The rip rap should be angular in shape, hard, and resistant to weathering. |
| 3.5 | Rip rap shall be placed immediately following preparation of banks. |
| 3.6 | Prior to placement of rip rap, banks should be graded to a uniform slope no greater than 1.5 horizontal to 1 vertical. See figure 1. - Typical cross section of rip rap stream bank protection. |
| 3.7 | Filter layers of either 150 mm (6") of well graded gravel {fine sands through 75 mm (3") stones with no stones exceeding 150 mm (6")} or geotextile filter fabric shall be placed on graded bank prior to the placement of rip rap to prevent the loss of bank material through the voids in the rip rap. |
| 3.8 | The minimum thickness of the rip rap shall be 1.5 times the maximum stone size (or 2.25 times the D50). |
| 3.9 | The rip rap shall be deposited to the full thickness in one operation and placed as a dense, well graded mass of stone with minimal voids. |
| 3.10 | Rip rap shall be anchored at the base of the existing bank by placing the bottom of the rock in a trench excavated to a depth at least equal to the height of the largest rock. |
Figure 1.Typical cross section of Rip Rap Stream Bank Protection
The New Brunswick Department of Agriculture, Fisheries and Aquaculture reserves the right to revise the above standard at any time.
Table 1.Suggested Minimum Rip-Rap Gradings for Stream Bank Protection.
| Class I | ||
| Nominal 12 inches diameter or 80 lb. weight. Allowable local velocity up to 10 ft/sec. Grading Specification: |
||
| 100% smaller than 18 inches or | 300 lb | |
| at least | 20% larger than 14 inches or | 150 lb |
| at least | 50% larger than 12 inches or | 80 lb |
| at least | 80% larger than 8 inches or | 25 lb |
| Class II | ||
| Nominal 20 inches diameter or 400 lb. weight. Allowable local velocity up to 13 ft/sec. Grading Specification: |
||
| 100% smaller than 30 inches or | 1500 lb | |
| at least | 20% larger than 24 inches or | 700 lb |
| at least | 50% larger than 20 inches or | 400 lb |
| at least | 80 % larger than 12 inches or | 70 lb |
| Class III | ||
| Nominal 30 inch diameter or 1500 lb weight. Allowable local velocity up to 15 ft/sec. Grading Specification: |
||
| 100% smaller than 48 inches or | 5000 lb | |
| at least | 20% larger than 36 inches or | 2500 lb |
| at least | 50% larger than 30 inches or | 1500 lb |
| at least | 80% larger than 20 inches or | 400 lb |
| Note the percentages quoted are by weight; the sizes quote are equivalent spherical diameters, = 1.24 volume;< /FONT > | ||
| The relative density is assumed to be in the range 2.4 to 2.9. | ||
Table 2. Rip rap Minimum D50 Sizing Chart.
| Water Velocity (feet / second) |
Rock D50 (inches) |
Rock Weight (pounds) |
| 5 | 4 | 3 |
| 6 | 6 | 10 |
| 7 | 8 | 24 |
| 8 | 10 | 47 |
| 9 | 12 | 81 |
| 10 | 15 | 158 |
| 11 | 18 | 273 |
| 12 | 20 | 375 |
| 13 | 24 | 650 |
| 14 | 27 | 925 |
| 15 | 30 | 1268 |
| 16 | 35 | 2013 |