Flood Hazard Areas

Flood hazard assessments have been carried out for several areas in the District. These include the Poverty Bay Flats, Gisborne urban area, and the Mangatuna/ Wharekaka Area for the Hikuwai/Uawa River. The flood hazard varies across liable areas. Generally towards the edge of the flooded area depths are shallow and floodwaters move at slow speeds. Therefore the degree of hazard is low. However floodwaters are generally deep and flow swiftly in the vicinity of the main river channel and other major flood flow paths. These areas generally have a high degree of flood hazard with silt and debris deposition. The process of assessing flood hazard, firstly involves a study into flood behaviour. This involves estimating discharge for the various sized floods and the determination of water levels, velocities and depth of flooding. Then secondly a design flood standard' is selected. The determination of thatdesign flood standard' balances the social, economic and ecological considerations against the consequences of flooding. If the standard is too low development will be inundated relatively frequently with greater damage. If the standard is too high land will incur unwarranted controls. The selection of the design flood standard depends on flood behaviour, landuse and consequences of larger floods. The level of protection offered by flood mitigation works may be different from the design flood standard adopted for land use planning. That level is dictated by economics of the situation or physical limitations of the site. It is prudent to assume that floods may occur greater than the ability of protection works to contain them. The design flood standard is intended to reduce the impacts of such floods, by avoiding or limiting development which would be affected.

Data and Resources

Additional Info

Field Value
Theme ["geospatial"]
Author
Maintainer GisborneDistrictCouncil
Source http://geoportal-gizzy.opendata.arcgis.com/datasets/393b1dae98074e24b983eec70e0a5d7a_0
Created 2019-09-21T07:39:20.000Z
Date modified 2019-09-21T07:48:11.000Z
Language English
Spatial {"type": "Polygon", "coordinates": [[[177.7875, -38.7864], [178.3163, -38.7864], [178.3163, -38.1254], [177.7875, -38.1254], [177.7875, -38.7864]]]}
Source Identifier http://geoportal-gizzy.opendata.arcgis.com/datasets/393b1dae98074e24b983eec70e0a5d7a_0
Record created December 9, 2019, Last Updated March 3, 2020