Wave Run Wave run is the maximum vertical extent of wave action on a beach or structure above mean sea level. Wave setup Wave setup is the rise in average water level due to the presence of breaking waves.
Purpose
Summary of Seawater Inundation Calculation and Freshwater Inundation Process 4
The practice note also outlines the general process for determining minimum ground and/or floor levels in areas subject to freshwater flooding. Some sites in the Nelson and Tasman districts may be subject to both seawater and freshwater inundation.
Inundation hazards and scope of practice note
There are many factors that contribute to potential freshwater flooding risks and these must be considered for each site at each site. The highest value of the three calculated levels determines the minimum ground and/or floor level.
Exceptions
Therefore, a site-specific assessment of the proposed development, taking into account specific hazard impacts (by applying local adjustment factors), may still be required. Please note that properties declared not subject to flooding under this practice note methodology may still be at risk of flooding hazards in more extreme or unpredictable weather conditions than permitted.
Councils’ inundation information
Where this modeling has yet to be performed, secondary flow paths will be considered as a 'local adaptation factor' (see section 3.6.3). The Council will be able to advise on what information is kept to support the calculation of the minimum ground and/or floor levels in these situations.
Resource Management Act 1991 and Building Act 2004
Furthermore, to achieve this, it will need to be demonstrated that there are no adverse effects (increased flood levels, diversion of flood flows and/or secondary flood routes) occurring on adjacent or surrounding property in response to this design flood event. For other development (on existing titles) subject to the RMA 1991, the practice note process will be the same as for subdivision and development as described above.
Introduction
Development considerations
Identifying locations subject to seawater and/or freshwater inundation hazards
Check if your site is subject to freshwater flooding and determine the soil and/or. Check if your site is subject to freshwater flooding and determine the soil and/or floor.
Seawater and freshwater inundation design events
Land up to at least this level may be affected by seawater inundation depending on shoreline slope or other factors. These areas may also be affected by freshwater inundation impacts (eg at estuarine sites) and this hazard must also be considered both in isolation and in combination with seawater inundation. Similarly, there may be both seawater and/or freshwater flooding in low-lying areas more than 30m away from MHWS-6 and should be considered.
If the ground level of a site is between RL 4 m and 6 m, the risk of freshwater and/or seawater flooding hazards may be present separately or in combination (depending on the distance from MHWS-6) and the highest value of the three calculated levels determine the minimum ground and/or floor level. Above RL 6m freshwater inundation is likely to predominate, but also check for possible seawater inundation next to steep coasts where the upper beach slope is >20%.
Seawater Inundation Calculation
For more information or guidance on what flood risk may be present on your site, please contact the relevant Council. 4 Properties where land is closely associated with a building subject to flooding in a 1% AEP event may require a hazard notice under s73 of BA 2004. S71-74 of the Building Act apply if you propose to build on land that subject to natural hazard(s).
The height determined from the above process is the minimum ground and/or floor level required, relative to RL 0m (NZVD2016). Note: There may be additional freeboard requirements for new buildings and alterations based on E1 or E2 of the Building Code.
Storm Tide Adjustment Factor
Beach gradients are the average of many measurements taken between the 2.0 m and 2.5 m LiDAR contours (NZVD2016). The data is very sensitive to the beach slope used and for a specific design the top beach slope measurement should be checked. The Coastal Calculator uses the Stockdon et al (2006) formula for wave set-up and run-up, developed for sandy beaches only.
The formula uses a constant beach slope and so for compound slopes as is generally the case, an upper beach slope is recommended and used, as this will conservatively return a higher wave configuration and wave runoff value. The calculator also assumes that the slope of the beach used remains constant for any selected sea level rise scenario - this may not be the case in reality due to the effect of a number of factors such as shoreline erosion, changes in sediment composition near the coast and the like.
Freeboard
The above data excludes those parts of the coast that are partially or fully affected by rock revetments or other structural interventions, for example at The Haven, Riwaka, Ruby Bay in the south, Motueka in the south, the middle of the Kina Peninsula, the middle of Pakawau and much of the Pupongo coast .
Freshwater Inundation Process
Combined seawater and freshwater inundation
Determining the minimum ground and/or floor level
Options for raising ground and/or floor levels
Subdivision or buildings on river floodplains, areas of freshwater pools, and in locations where seawater overflows (either from wave run-up or pools on lower land), where construction platform filling can be performed and there are less than minor adverse effects from-site. Buildings on river floodplains, freshwater pools and in seawater overflow locations where building platform fill can be performed to a small degree to reduce nuisance flooding (e.g. a 20% AEP event) without off-site adverse effects, but where the filling for a construction platform off-site has more than minor adverse effects. Buildings on river floodplains, freshwater pools, and in seawater overflow locations, where filling a build platform has more than minor adverse effects beyond the site.
Introduction
Seawater and freshwater inundation design events
The MHWS-6 tide is used for the tide base condition from which the hydraulic level line is calculated, for discharges from open channels and pipelines terminating in the coast. This is to ensure that the effect of a 1% AEP rainfall/runoff event on the drainage network is appropriately simulated or designed for the development under consideration, without imposing an improbable tidal boundary (such as the highest astronomical tide) which would unnecessarily affect rainfall. discharge to the coast. This practice note assumes that reasonable joint probability limits have been established to provide a practical and affordable basis for design.
Identifying locations subject to seawater and/or freshwater inundation hazards
Supporting information to inform the Seawater Inundation Calculation
The main factors influencing the risk of seawater flooding are storm surge, wave build-up, wave run-up and sea level rise. That is, at high tide, the sea level within the estuary and on the open coast is actually equal. Within the calculation of seawater inundation, the climate change factor (CCE) takes into account the expected sea level rise.
The CCE factor applies the transitional values of sea level rises shown in Figure 3. The CCE factor does not take into account increased rainfall or increased frequency of storm events. Transition values for sea level rise for categories 'C' (existing development) and 'D' (short-term non-habitable assets) within Table 5 correspond to the equivalent values recommended for sea level rise from the previous MfE guidance (MfE, 2008a) .
Supporting information to inform the Freshwater Inundation Process
Using the H+ scenario provides a future for the expected longer life of new development and informs the NZCPS requirement to avoid the risk of future hazards prior to planning. To inform cases where reinforcement of existing development is inadvisable (category 'B'), the guidelines do not provide for a transitional value and instead a comprehensive approach to planning flexible MfE pathways should be used. Until each council advances the flexible planning pathways approach, as detailed in the MfE guidance, planning processes will use sea level rise thresholds for each of the development settings (as shown in Table 5). 2120) should be used in determining the 1% flood event AEP for the year 2120 when flood levels for subdivisions and new buildings are considered in accordance with RMA 1991 procedures.
Supporting information relevant to both the Seawater Inundation Calculation and
Site specific LA factors should be discussed with Council to ensure that all factors are addressed and appropriate minimum ground and/or floor levels are determined. The issues listed below are not exhaustive and there may be further aspects to consider when determining the LA factor (including those listed in section 4). Risk of freshwater/seawater flooding associated with increased tidal impact Ground and/or floor level elevation may also be necessary in an area where stormwater/.
As sea levels rise, more frequent and/or longer retention of rainwater may be required before drainage can take place. The following section describes maintenance issues that should be considered as part of any proposed new development and that may affect the minimum ground and/or floor levels as a local adjustment factor.
Dwellings and onsite effluent and stormwater disposal
However, except for buildings with a specified short life, the effects of sea level rise apply after a 50-year time frame, depending on the nature and duration of the building's use, in accordance with central government guidance, the NZCPS and decisions of the Environment Court. Where short-lived buildings or assets are proposed, the minimum required floor height may be reduced below that required to mitigate long-term, extreme hazard exposures, depending on the use of the building or asset.
Reticulated stormwater servicing
Backwater
Settlement due to liquefaction
Building use and risk
Further considerations for owners and designers
Where there are multiple uses proposed for a new building (eg one bedroom garage), the Council will consider the function of the building and require that floor levels be raised to ensure that the most at risk (where it is an occupied building) to be protected from flooding. Under section 71 of BA 2004, a property may be considered to be subject to a natural hazard and an assessment is required to determine whether the occurrence of the hazard has been considered. Thus, it may be possible to meet Building Code requirements by having a minimum floor level set above the 2% AEP flood level, but still be subject to a title hazard notice because the land on which the building is located is closely related to being subject to flooding.
In order to avoid any consent notices under Sections 72 and 73 of the BA 2004, a property owner will generally need to ensure that both the floor level and land intimately associated with the building is above the 1% AEP flood level. This means that the Council will endeavor to avoid development in flood risk areas where possible, or to mitigate the risk exposure of the development to the greatest extent practical.
Superseded vertical datums
