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Describing a wetland and catchment areas

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  • Updated

Fenced off wetlands should be entered as a wetland block. If artificial wetlands are used to treat outlets, these should be added as a wetland within a block (under the drainage tab). It is important that the same wetland is not included more then once.

 

Wetland Condition

There are four types of Fenced Wetland conditions:

  • Natural: (Class 1) is defined as fenced, well vegetated, with evenly distributed surface flow and no channelisation.
  • Artificial Type 1: Flow path length to width ratio >5 (2 or more stage wetland, with even elongated channel or serpentine path created using internal bunds), well vegetated with good dispersion and even flow through the majority of wetland and minimal channelisation or dead-zones.
  • Artificial Type 2: Single stage wetland with flow path length to width ratio >3, well vegetated with even flow through majority of wetland and minimal channelisation or dead-zones
  • Artificial Type 3: Single wetland with length to width ratio >3. Still well vegetated, but with some potential for flow channelisation and short-circuiting.

There are eight types of Unfenced Wetland conditions:

  • Natural Class 2: Unfenced. Lightly grazed by sheep. No visible signs of pugging. Surface flow even distributed.
  • Natural Class 3: Unfenced. Lightly grazed by sheep or set stocked cattle in summer - not mob grazed by cattle. At most minor pugging damage. Signs of channelisation.
  • Natural Class 4: Unfenced. Accessible by cattle. Signs of pugging damage. Signs of channelisation.
  • Natural Class 5: Unfenced. Highly channelised wetlands. Deeply incised. Inflowing water bypasses vegetated, organic soils.
  • Artificial Type 1: Flow path length to width ratio >5 (2 or more stage wetland, with even elongated channel or serpentine path created using internal bunds), well vegetated with good dispersion and even flow through the majority of wetland and minimal channelisation or dead-zones.
  • Artificial Type 2: Single stage wetland with flow path length to width ratio >3, well vegetated with even flow through majority of wetland and minimal channelisation or dead-zones
  • Artificial Type 3: Single wetland with length to width ratio >3. Still well vegetated, but with some potential for flow channelisation and short-circuiting.

For more information on wetland conditions, see the NIWA Wetland Condition Guide here

 

Wetland Type

There are five wetland types you can select:

  • Default
  • Type A: Water always flows. Dominated by sedges and reeds. May contain flaxes, willows, etc. 
  • Type B: Flows most of the year. Dry in drought.Abundant sedges and rushes.
  • Type C: Flows in autumn, winter and spring. Dry in summer.Some sedges and reeds. Dominated by pasture grasses.
  • Type D: Only flows during rain. Pasture grasses.

 

Catchment Details

Catchment Area

The catchment area of a wetland is the upslope area, bounded by natural features such as hills or mountains that drains surface and sub surface water flows into the wetland. It is sometimes also referred to as the watershed, drainage basin or contributing area.

 

Catchment Convergence

Wetland convergence is a measure of the percentage of shallow runoff (surface and sub-surface drainage) that flows into a wetland. The rest enters the stream directly. This depends on the landscape that drains towards the wetland.
If the topography converges towards the viewer, then we suggest using a High convergence. In easy country, most flow converges into ephemeral channels and if these are well vegetated and ideally fenced, then convergence can be high.
If the viewer is in a small depression to which only a small proportion of the property drains AND the other parts of the property do not drain to wetlands, then we suggest using Low convergence.

 

Aquitard Depth

Aquitard depth is the depth down to the soil layer that is impervious to soil water, or where soil drainage is very slow. Seepage from road cuttings, or the depth of a hard layer in post holes may indicate the aquitard depth. In pallic soils, aquitard depth is usual less than 1m.

 

Catchment distribution

The drainage input from a catchment into the reservoir can come from more than one block. The proportion of blocks contributing to drainage can be specified by the user (check box), or a default allocation is assumed:

If the box is check you will need to specify:

  • Which blocks are part of the catchment
  • The percentage or area of the catchment that each block contributes
  • Any remaining area will be attributed to an Off farm source - Similar to farm, Intensive dairy, average dairy, Sheep/beef, Bush forest.

 

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