The Putrajaya constructed wetland system comprises of six arms with 23 cells as described in Figure 1. All the arms (except of Upper Bisa) eventually discharge to the Central Wetland, which make the 24 cells in all, before the water flows down into the Putrajaya Lake. They straddle the water courses of Sungai Chuau, Sungai Bisa and three tributaries. A series of rockfilled weirs was constructed along the six arms of the wetland to divide the 24 cells. Although all the six arms are connected, they differ in size, depths, plant communities and pollutant loads that it is designed to handle.
Figure 1 : The Putrajaya Wetland Cells and its location
The basic processes happening in the cell zones are illustrated in Figure 2. Typical longitudinal cross-section and typical layout of a wetland cell are shown in Figure 3 and Figure 4 respectively.
The design features a multi-cell multi-stage system with flood retention capability to maximize the space available for colonisation by water plants. The roles of the plants are to intercept pollutants and to provide a root zone where bacteria and microorganisms can flourish to assist in filtering and removing water pollutants.
Figure 2 : Various reactions happening in the wetland cells
Figure 3: Longitudinal section of a typical wetland cell showing the Zone of Intermittent Inundation (F2 and F1), Wetland Zone (Zone 1, 2 and 3) and the Open Pond
Figure 4 : Typical Layout Of A Wetland Cell
The Putrajaya Wetland cells and its structural components are the keys to the functioning of the wetlands for cleansing the river water. They are important in maintaining the broader 'functional capacity' and objectives of the wetlands, which include providing a habitat for local fauna, primarily mammals, water birds, reptiles, amphibians, fish and invertebrates; hydrological modification (by providing flood detention area and reducing peak discharges and flow velocities) and recreation (the wetlands are used for both passive and active recreation, and parkland for aesthetic and recreational value).
The principle features of the wetland are shown below :
Principal Features of Putrajaya Wetlands (Area in hectares)
Weirs & Islands
Zone of Intermittent Inundation
Details of the wetland cell structural components and the wetland vegetation species and its proper location within the cell are explained and summarized below :
The Wetland Cell Structural Components And Its Function
Allows water to flow into the wetland cell
Protects the bed of chnnels and inlet and reduces erosion by reducing the energy of incoming water. May be applicable to any part of the wetlands where there are potential erosion problems.
Waterplants provide support for microbial biofilms which facilitate nutrient transformation, organic flocculation, filtration of pollutants, inhance sedimentation and provide oxygen to sediments.
Enhances bacterial decomposition of organic matter.
Provides a range of habitats for macro and micro fauna.
Provides visual contrast through different textures, sizes, shapes and colours.
Enhances settling of finer soil and sediment particles (that would otherwise pass through a GPT) and associated pollutants such as heavy metals, nutrients and pesticides adsorbed by the sediments.
Reduces sediment loads to reed beds ensuring higher clarity for effective plant growth.
Improves water quality both within and downstream of the cell and, in turn, the ecosystem health.
Allows UV (sunlight) penetration into the water for disinfection.
Enhances mixing of the water and reduces short circuiting of flows.
Provides a deep water habitat for fauna, refuge during drought, landing and secure area for waterfowl. Meshes into the planted areas thereby enhancing visual beauty.
Provides isolated habitats for birds.
Provides a visual focus for the wetlands.
Edge water plants
Create habitat divesity along the shoreline for invertebrates and wading birds.
Improve water quality.
Physical barrier to human intrusion to the water.
Water level control structure
Allows capture of highly polluted flows for retrieval or recycling. Allows water level control for several purposes including:
Operation and maintenance;
Maintaining predetermined water regimes for greater habitat diversity or to specifically encourage particular species of flora/fauna;
Manipulation of water level for waterplant establishment.
Prevent litter and debris entering the cell. Impounds stream flows to create a pool. Sets normal predetermined designed operating water level in wetland.
The Wetland Vegetation Species And Its Proper Location Within The Structural Components Of A Wetland Cell
Wetland Strucural Component
Typical Water Depth
Shallow marshes can be expected to have a regular drying cycle or dry out in some years. Under this type of hydrological regime a diverse vegetation will develop (rushes, sedges and leafy herbs). The actual composition of the vegetation can be expected to change as a response to fluctuations in water level. Vegetation cover can also vary from sparse to dense depending on the species and the water cycle.
Eleocharis spiralis, E. variegata, Scleria cyathophora, Carex indica, Cyperus pulcherrimus, Fimbristylis spp.. A number of dicotyledonous species will also occur in this zone, eg. Clerodendron spp., Lagerstroemia spp., Polygonum spp., Ludwigia spp.
As depth of inundation and duration increases vegetation diversity tends to decrease. Permanently inundated marshes with water depths greater than 0.6m are frequently dominated just a few species which will often form a very dense cover of vegetation. The actual species will tend to differ from marsh to marsh. However the species that tend to dominate these habitats are nearly always clonal species with large underground rhizomes.
As water depth increases the diversity of emergent marsh vegetation is further limited by the size of the plant. To survive in deep water plants must be able to grow to about twice the water depth. The vegetation of deep marshes is generally of medium to sparse cover and dominated by just a few species. The species that tend to dominate these habitats are always large clonal species with substantial underground rhizome systems.
Water depths greater than 1.5m will restrict most emergent aquatic macrophytes and thus result in open water zones. Many submerged and floating plants are capable of colonising and growing in this type of environment. Depending on the turbidity it is almost inevitable that this zone will be colonised by some aquatic plants. Regular monitoring of these zones will be required to ensure any invasion of an undesirable weed species is quickly detected and controlled. Colonisation of these zones by acceptable species a benefit as they contribute to enhanced sedimentation and fine particle filtration and provide habitat for aquatic invertebrates and fish.
Water depths greater than 2.5m will restrict most rooted emergent and submerged aquatic macrophytes particularly in constructed wetlands designed for water quality control where water turbidity becomes a limiting factor. Typically only floating plants will occur in these zones. As for ponds, regular monitoring of these zones will be required to ensure undesirable weed species are detected and controlled.
Where these zones are positioned at the inlet to a wetland they are the primary sediment traps for the treatment system so any vegetation that does happen to establish or develop will be regularly disturbed when sediment is being removed from the pond.
Myriophyllum, Potamogeton, Vallisneria, Nymphaea.
Weed Risks: The likelihood of significant submerged plant growth in these zone is relatively low but the risk of floating weed invasion is very high. For example Salvinia molesta, Eichhornia crassipes, Pistia stratiotes, Ipomea aquatica.
Wetland Fringing Zones
The edges and surrounding area of wetlands typically experience large variations in inundation depth, frequency and duration. The zone immediately above and below normal water level usually experiences the greatest variation. This zone commonly supports fringing marsh and swamp vegetation adapted to regular but short duration inundation. With increasing elevation inundation frequency and duration in particular decreases. Under these less restrictive conditions for plant growth a range of woody vegetation can develop. Typical examples are riparian and floodplain swamp forests.
Hydrologically this zone has similar inundation depths as the Shallow Marsh zone but normally increased frequency and reduced duration. As a result there are a very great number of plants that can occur in this zone ranging from sedges and rushes through leafy herbs to woody shrubs and trees.
This zone can support a great number of species and suitable plants can be selected from the following genera, eg. Cyperus, Eleocharis, Limnophila, Ludwigia, Polygonum, Pandanus, Eugenia, Barringtonia.
Hydrologically this zone is very well watered with regular inundation periods but is also regularly drained well enough to support large woody vegetation. Tropical swamp forests are typically very diverse systems both floristically and structurally and dominated by small to medium sized trees.
This zone can support a great number of species and suitable plants can be selected from the following genera, Eugenia, Dipterocarpus, Fagraea, Ficus, Ixora, Lithocarpus, Litsea, Pandanus, Podocarpus, Shorea, Tarenna, Tristania, Xanthophyllum.
The Putrajaya Lake
The lake is at the southern part of the wetland. About 60% of the lake water flow from the wetland and the remaining 40% is the direct discharge from bordering promenade. The 20 m width promenade is the buffer feature along the lake shorelines. The water surface area of the whole lake is about 400 hectares. The total volume of the whole lake water is about 23.5 million cubic meters and the water depth is in the range of 3 to 14 meters. The lake has been planned to cater for multi-functional uses, including recreation, fishing, water sports and water transport. The lake and its foreshores also form Putrajaya's most popular resource for informal recreation as a waterfront city.
The principle features of the lake are shown below.