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Fairway and Berm Condition |
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Fairway and Berm Condition |
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Environment Canterbury |
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<DIV STYLE="text-align:Left;"><DIV><DIV><P><SPAN>“Fairway and berm condition” shows an assessment of the adequacy of the river fairway for capacity and the left and right berms for resistance to erosion. Both are measured on a 1-5 scale, with 1 being ideal/highly resilient, 3 being adequate/fit-for-purpose and 5 being very poor/inadequate. These are generally assessed from aerial photographs, but may be supplemented by on-the-ground and topographic survey information where available.</SPAN></P><P><SPAN /></P><P><SPAN>Adequacy of fairway is measured in comparison to the “vegetation control lines” (see separate layer) where available. It is primarily based on the width of the open channel visible in aerial photographs, downgraded with the presence of obstructions such as woody weeds. Where survey information is available and shows aggradation (bed level build-up) above target mean bed levels (based primarily on modelled flood capacity), the fairway score is downgraded. A clear fairway the same or greater than the control width would score a “1”, while a fairway congested by more than about 40% compared to the vegetation control lines would score a “5”. The desired fairway widths in the vegetation control layer are based on the river widths observed on a series of aerial photos, which takes into account variations in flood sizes over different periods of time. A consistent width is chosen for each reach of river to promote even distribution of energy and reduced erosion risk. Refer to River Corridor Assessments (Ashburton, Rangitata, Waitaki, Waimakariri) for more background.</SPAN></P><P><SPAN /></P><P><SPAN>The adequacy of berms to resist erosion is based primarily on berm width, tree density and uniformity and adequacy of the “front edge” of erosion protection. Where possible, this is supplemented by information on tree age, species and extent of weed infestation (especially Old Mans Beard). As a guide, a good minimum berm width of dense trees (willows or poplars) is about a quarter of the adjacent fairway width – this would score a “3”. An equivalent could be twice the width but with scattered trees. A more resilient berm, half the width of the fairway in dense trees (or equivalent) would score a “1”. The River Corridor Assessments explore the relationships between fairway width and the size of meanders, which guide judgements about adequate berm width.</SPAN></P></DIV></DIV></DIV> |
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<DIV STYLE="text-align:Left;"><DIV><P><SPAN>This work is licensed under a Creative Commons Attribution 3.0 New Zealand License</SPAN></P></DIV></DIV> |
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Fairway and Berm Condition |
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["Engineering","Fairway","Berm","Condition","Water","River","Ashburton","Ashley","Rakahuri","Waimakariri","Hakatere"] |
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en-NZ |
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20000000 |
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