Laserfiche WebLink
<br />FLOW <br /> <br />. <br /> <br />s <br /> <br />I- <br /> <br />-I <br /> <br /> <br />L <br /> <br /> <br />20 0 Expansion <br />Angle <br /> <br />Bankline <br /> <br />t;~\'+\tFt?~t'it~~Y;~C:=0GS*:"-,-_,,,~}L"t.-,- --'@~ <br /> <br />LK <br /> <br />LK= S tan(200) - L <br /> <br />Figure 1.3 Length of key for mild bends <br /> <br />When the channel radius of curvature is small (R < 5W) and S < Utan(200) <br /> <br />L (W )0.3 (S)0.5 <br />LK=- - - <br />2 L R <br /> <br />(laGrone 1995) <br /> <br />NOTE: LK should not be less than 1.5 times the total bank height. <br /> <br />The NRCS guideline for length of key (LK) for short weirs or barbs (Saele 1994) is to key the <br />barb into the bank a minimum distance of 2.4 m (8 It) or 4 (0100) which ever is greater. <br /> <br />8. TOP WIDTH - The top width of the weir may vary between 1 m and 4 m (3 and 12 It), but <br />should be no less than (2 to 3)*0100, Weirs over 9 m (30 It) in length will have to be built <br />either from a barge or by driving equipment out on the structure during low flows. Structures <br />built by driving equipment on the weir will need to be at least 3 to 5 m (10 to 15 It) wide. <br />Side slopes of the weirs can be set at the natural angle of repose of the construction <br />material (1V:1.5H) or flaller. <br /> <br />9. NUMBER OF WEIRS - The smallest number of weirs necessary to accomplish the <br />project purpose should be constructed. The length of the weirs and the spacing can be <br />adjusted to meet this requirement. Typically, not less than three weirs are used together on <br />unrevelled banks. <br /> <br />10. CONSTRUCTION - Construction of the bendway weirs are typically conducted during <br />low flow periods for the affected river. Construction methods will vary depending on the <br />size of the river. Construction on larger rivers may be conducted using a barge which would <br />allow the rock to be placed without disturbing the bankline. For rivers where a barge is not <br /> <br />1.7 <br />