Presentation on theme: "Variances ID areas where flood boundaries exceed zoning (e.g. jurisdiction of marsh act) MMRA Mandate = protect agricultural land (allows periodic flooding)"— Presentation transcript:
Variances ID areas where flood boundaries exceed zoning (e.g. jurisdiction of marsh act) MMRA Mandate = protect agricultural land (allows periodic flooding) boundary based on HWL (CGVD28 datum) from 1950s, unique to each marsh body Tregothic Marsh (Windsor): Total assessed value = $31,003,300 yet agricultural land ~0.6%, majority commercial or government infrastructure
Two animated slides removed to reduce file size.
‘critical’ elevation determined for each marsh body (based on HWL & exposure) ‘construction’ elevation = 2 ft + critical in order to maintain slope, as increase height, must increase footprint Original Fundy design: 1:3 seaward 1:2 landward
210 m < critical 3.7% of dyke length foreshore mean = 220 m
Mechanisms of Dyke Failure
Bishop Beckwith Starrs Point foreshore marsh is critical for erosion protection & source of material (borrow pit) for dyke topping to decrease cost 1 m water depth – wave dissipation in 80 m
Important to re- examine marsh body boundary In many areas, strong match with historical HWL survey and lidar analysis. However, HWL determined from 1940s and did not consider CC Extend boundary if minimal development
Source: Pilarsky, 1998 hold the line & protect assets topping requires increase in base footprint, potentially extend dyke source of material (cost) armouring (toe of dyke or foreshore) cost benefit analysis required
Dyke heightening (cm) Cost of heightening or damage (M$) Example of cost assessment for dyke heightening in the Netherlands Example of cost assessment for dyke heightening in the Netherlands (van Alphen, 2012) The economic optimum level of protection is where the sum of investments in dikes and residual damage (continuous line) shows a minimum, i.e. where further increase of dike height doesn’t outweigh the related avoided damage anymore.” (van Alphen, 2012).