Wetland Identification & Delineation

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Wetland Identification & Delineation

Identification of Wetland/Reperian habitats

Classification of watercourses

Watercourses in catchments can be divided into three Sections (Section A, B and C) depending on their position relative to the water table.

SECTION A watercourses are the most headward streams in the river network and are situated well above the water table (Figure 1).

This means that water flow only occurs in these waterways during heavy storms and this flow is of a short duration. As a result they do not support a riparian habitat, i.e. no wetland vegetation (sedges and reeds), and soils are not hydromorphic (soils which show colours associated with intermittent or permanent saturation - mottles or gleying)

Figure 1: Section A Watercourse
Identification of Wetland/Reperian habitats

SECTION B watercourses occur where the watercourse bed is situated in the zone of a fluctuating water table (Figure 2). In other words, there is water flowing in the stream-bed for periods of a year. The amount of flow depends on the current height of the water table.

During dry periods, the stream may not flow but residual pools are often observed.

Figure 2: Section B Watercourse
Identification of Wetland/Reperian zones

SECTION C watercourses are in permanent contact with the water table and are therefore perennial streams that would flow throughout the year in a normal season (Figure 3). The watercourse gradient is flat and wetland vegetation and hydromorphic soils occur in these sections.

Figure 3: Section C Watercourse

Section A watercourses are the least sensitive watercourses in terms of hydrological processes and therefore these areas can be planted to timber. However, Section A watercourses must be evaluated individually in terms of suitability for crop establishment. If suitable for establishment, precautions must be taken to protect these areas from erosion as they do occasionally carry surface water.
Classification of a Wetland

Any land that is wet close to the soil surface, for long enough periods for anaerobic (no or very little oxygen) conditions to develop, can be defined as a wetland. Wetlands are characterised by wetland vegetation and hydromorphic soils.

In steep terrain, wetlands can take the form of seeps, sponges and springs.

On flatter terrain, they are found around dams, lakes, pans and floodplains.
Demarcation of Wetland/Reparian zones

Once the watercourses and wetlands on a farm have been identified, the next step is to demarcate the boundaries of these areas.

A wetland habitat can be divided into three zones (Temporary, Seasonal and Permanent) according to the degree of soil wetness (Figure 4).

The important boundary to be able to determine is the edge of the Temporary zone, as this will demarcate the edge of the wetland habitat. Vegetation and soil characteristics are used to define this boundary.

Figure 4: Cross section of a wetland/raparian habitat
Demarcation of Wetland/Riparian zones

Vegetation

If a riparian habitat is undisturbed, it is possible to visually determine the edge of the Temporary zone by seeing a change in vegetation colour.

In grassland dominated habitats, this is due to a mixture of species; those that occur extensively in non-wetland areas, and those hydrophytic plant species that are restricted largely to wetland areas.

The hydrophytic species are sedges and wetland grasses (e.g. Paspalum spp., Andropogon spp., Eragrostis plana, Eragrostis planicumis, Imperata cylindrica, Setaria sphacelata, Pennisetum spparistida junctiformis).
Demarcation of Wetland/Riparian zones

Soil factors

A more accurate way of defining the edge of the temporary zone is to look at soil characteristics. This is because vegetation has often been modified through agricultural activity.

These characteristics can only be determined by using a soil auger to remove a core of soil from the soil profile.

If hydromorphic soils with signs of wetness within 50 cm of the soils surface are observed then the area is classified as a wetland habitat (figure 4 on page 5).

The signs of soil wetness that would be observed are a greyish background matrix to the soil and mottles in the soil (figure 5 overleaf). The point where these signs of wetness are found at a depth of 50 cm is the boundary of that habitat, i.e. the edge of the wetland.
Demarcation of Wetland/Riparian zones

Typical Wetland Soil Horizons



Demarcation of Wetland/Riparian zones

Buffer Strips

The demarcated wetland/riparian area needs a buffer strip around it to protect the habitat and water resource.

This is particularly important with a deep-rooted crop such as timber. The timber industry has agreed on a 20 m buffer strip, delineated from the outer edge of the wetland/riparian habitat (edge of the Temporary zone).

A certain amount of flexibility is allowed - there will be specific cases for widening or narrowing the buffer strip, e.g. existing roads that cannot be relocated for practical or economic reasons. However, any narrowing of the strip must be substantiated and documented.

Wherever possible the buffer should be bordered by a valley bottom road which will act as a practical boundary for the maintenance of the riparian habitat. Ideally, these roads should be grassed.