Wetlands are determined by:
Wetlands do not have to be saturated with water all year round… but they do have to be saturated intermittently. The hydrology needs to be monitored over at least a year which makes it impractical for most assessments.
Wetland (hydric) soils are defined by the water saturation. Soils are useful in defining a wetland because spot samples are definitive. However, the Resource Management Act definition is silent about soils.
Various plants and animals that are adapted to wet conditions are good indicators of wetlands. There is a national protocol for defining wetlands based on vegetation (Clarkson, 2014). All plants have been given ratings on a scale of 1-5 for how much they need wet conditions. Some plants have a specialized need for a wet root zone.
To help assess whether an area is a wetland these classes are used:
| Class | Description | Probability |
|
OBL |
Obligate Wetland. Rarely in uplands (drylands). | Estimated probability >99% in wetlands |
| FACW | Facultative Wetland. Usually in wetlands, occasionally in uplands | 67-99% |
| FAC | Facultative. Commonly occurs in wetlands and uplands | 34-66% |
| FACU | Facultative Uplands. Occasionally in wetlands but usually in uplands | 1-33% in wetlands |
| UPL | Obligate Upland. Rarely in wetlands, almost always in uplands | <1% |
The first three indicator groups (OBL, FACW, FAC) are indicative of a wetland. In order for an area to be called a wetland, its dominance test must be over 50% and its prevalence index = or < 3.
The dominance test is the percentage of dominant species across all strata that are OBL, FACW or FAC. The three strata are trees/canopy, understory/shrubs and herbs/groundcover. Dominant species are all plant species that cumulatively cover immmediately in excess of 50% of the total vegetation cover in each stratum (when ranked from highest to lowest cover), and any additional species that cover at least 20% of the total cover in the stratum.
The prevalence index is a vegetation based system of weighted averages incorporating the percentage cover of species and their affinity for wet conditions. The species cover percentages are multiplied by 1 for OBL species, 2 for FACW, 3 for FAC, 4 for FACU, and 5 for UPL, and the total is divided by the sum of percentage covers.
The presence of a couple of isolated OBL plants alone does not mean it is a wetland, just as the presence of a couple of isolated UPL plants alone does not mean it is dry land.
If a wetland is dominated by FAC plants and the dominance test and prevalence index do not agree, it is necessary to also look at the hydrology, soils, and whether the conditions are natural or disturbed.
This method is realistic and pragamatic and will result in smaller areas being mapped as wetland than using the “20% wetland plant cover” definition used in the past. The method is more scientifically robust and consistent with practices nationally. However, it is complex and needs relatively detailed botanical knowledge.
‘Boggy’ areas of pasture grasses and exotic rushes are excluded from the wetland definition (and rules that go with that) under the Tasman Resource Management Plan, and so are most wetlands not formed by natural processes.
If there is a wet area on your property you are uncertain about, and would like to develop or restore, feel free to contact council for a free site visit by a wetland ecologist. The ecologist can determine whether it is a wetland, define the boundaries and provide advice on how you can restore the wetland, or keep adjacent pasture dry while keeping the wetland wet.
The Tasman District Council is undertaking a project to identify and map all wetlands in the region as part of their requirements under the Resource Management Act and to improve the ability to make good land management decisions. The mapping is initially based on information Council already has, such as aerial and satellite images, and then refined through site visits.
Mapping will clarify to landowners and Council where the boundaries of wetlands lie. It will offer clarity to landowners who are often not certain as to what is or is not a wetland, and will more precisely identify where the wetlands rules apply and don’t apply on the ground.
Council aims to identify all wetlands on your property and map them accurately the first time, to provide clarity and certainty. But for some wetland types with forest or scrub canopy, such as pakihi, it can be difficult to identify all wetlands and to delineate the boundaries accurately from aerials. Where there are very gradual vegetation changes from wetland to dry land it is also difficult to confirm the boundaries from aerials.
A site visit is the best way to discuss concerns and confirm wetland boundaries. The wetland regulations apply to all wetlands in the district regardless of whether they are presently mapped. As imagery with better resolution becomes available, there is a possibility of the odd additional wetland being identified. You will be informed, and are welcome to request a site visit if you have concerns. If you have any unmapped boggy areas you plan to develop and would like to seek clarification on, you can also request a site visit.
You should decide if you would like to have a site visit. While the choice to have a site visit is a personal one and completely voluntary, there are considerable benefits:
A Council staff member and/or Council representative will visit with the purpose of answering any questions you may have, and will assess and photograph the wetland and map the boundaries. In some cases, there will be a need to do analysis of the botanical data before confirming the updated boundary.
After the site visit, Council will post landowners an updated map for each wetland site. You can also request an electronic copy to be emailed.
Land developments and stream diversions and dams that affect the hydrology of a wetland, or cause significant vegetation damage in a wetland, are a discretionary activity and require a resource consent. You are more likely to obtain consent for lower value wetlands, for example, those dominated by certain swarding ‘cutty grasses’.
If it is confirmed after the site visit that you have a wetland or wetlands on your property and you don’t agree, you will still have an opportunity to submit in opposition to all or part of your wetlands’ inclusion on the LIM for your property. Your submission must be in the form of a report, commissioned by you, from a wetland ecologist that produces evidence about the vegetation, hydrology and soil conditions to support any amendment to the boundaries. Council will consider this information alongside its own information prior to making a final decision. Any amendment will be governed by definitions in the regional plan.
Information about your wetland from a suitably-qualified ecologist is essential in order to debate boundaries of the wetland. If you disagree and don’t wish to have a site visit from Council, then the wetlands identified on your property, as shown on the enclosed map, will go onto the LIM for your property. However, you will still have an opportunity to lodge a submission.
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