CONTEXT: The area that I have chosen to work with is located on the east side of my proposed subdivision plan as shown above. The area of the site is 1000m2 and contains a medium density based dwelling, a low intensity road, and an ecologically rich wetland area which connects to the coast. A cross section from Urquhart Road to the east coast shows the landform and a large-scale understanding of the direction of storm-water. The concept that has driven this idea of design is based on the Low Impact Urban Design and Development (LIUDD) model that prioritizes natural systems and avoids the heavy footprint of urban influence. WHAT IS A RAIN GARDEN? Rain gardens help remove pollutants and slow down storm-water flows, recharge freshwater bodies and look attractive. They filter storm-water through soil mix and plants. These absorb and filter contaminants before storm-water flows to surrounding ground, pipes, drains and streams, and eventually to the sea. Rain garden soil mix: Most important component of rain garden â€“ the soil filters pollutants. Usually sandy loam, loamy sand or loam. Ponding area: Holds storm-water runoff until it seems through the planting mix and into the under-drain system. Plants (preferably native): Plants help filter pollutants and look attractive. Usually native plants as they are suited to the extreme wet/dry conditions (such as ponding for up to 24hrs) Overflow system: Bypass for excess flows when rain-garden pond is full. Sand layer: Additional storm-water filter, removing pollutants passing through the planting bed. Also helps retain soils within the rain-garden. Under-drain system: Water drains through soil mix to under-drain then is piped to stormwater network or waterways (e.g. stream, open water). Some free draining soils may not require under-drain, as runoff will drain to groundwater aquifers. WHAT IS A WETLAND? A wetland is a land area that is saturate with water, either permanently or seasonally, such that is takes on the characteristics of a distinct of ecosystem. Wetlands play a number of roles in the environment, principally water purification, flood control, and shoreline stability. Wetlands are also considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life. While wetlands occur naturally, they can also be constructed artificially as a water management tool, which may play a role in the developing field of water-sensitive urban design.
A PLAN Scale: 1:100
Instead of using an overflow system that directs excess water away, I have chosen an alternative way of dealing with this issue. It is capable to treat the water naturally, which would lower the influence of urban materials to the site. Allowing the storm-water to follow the topography of the site, sediments and pollutants is filtered through a series of grasses while creating a wetland area. The dense planting also brings a high level of biodiversity to the area and creates a comfortable habitat for fauna.
Common Name jointed rush, oioi mauri purei speckled sedge rautahi toetoe tree broom mikimiki tupari wiiwii napuka manuka ramarama tuhara harakeke flax lancewood
Average Height 1.5m 1.5m 1m 1m 0.5m 2m 4m 2m 2m 1m 2m 4m 5m 1m 2m 5m
Plant Type rush shrub sedge sedge sedge grass shrub shrub sedge sedge shrub tree shrub sedge shrub tree
Wetland species: Apodasmia similis Astelia grandis Baumea articulata Baumea juncea Baumea rubignosa Blechnum minus Bolboschoenus fluviatilis Carex dissita Carex geminata Carex lessoniana Carex secta Carex virgata Carpodetus serratus Coprosma propinqua Coprosma robusta Cordyline australis Cortaderia fulvida Eleocharis acuta Laurelia novae-zelandiae Leptospermum scoparium Phormium tenax Rhopalostylis sapida
jointed rush, oioi mauri jointed twig rush swamp twig rush baumea swamp kiokio marsh clubrush forest sedge cutty grass swamp sedge purei rautahi marble leaf mikimiki karamu cabbage tree toetoe spike rush pukatea manuka harakeke flax nikau
1.5m 1.5m 2m 1m 1m 0.5m 1.5m 0.5m 1m 1m 1m 0.5m 5m 2m 4m 8m 1.5m 0.5m 10m 4m 2m 10m
rush shrub rush rush rush fern sedge sedge sedge sedge sedge sedge tree shrub shrub tree sedge sedge tree tree shrub tree
Accessibility and connections around the site is created through the implementation of a low impact boardwalk. The elevated structure will create a trail for the community to enjoy passive recreation and escape the proposed subdivision area. Following the idea of Low Impact Urban Design and Development, timber will be used to create the structure, with stainless steel wiring to create a fence for obvious safety requirements. The trail can be an educational journey that showcases the varied habitats and biodiversity
Nutrient retention: A natural function of wetland vegetation is the up-take and storage of nutrients found in the surrounding soil and water. These nutrients are retained in the system until the plant dies or is harvested by animals or humans. Wetland purification: Many wetland systems possess biofilters, hydrophytes and organisms that in addition to nutrient up-take abilities have the capacity to remove toxic substances that have come from pesticides, industrial discharges and mining activities. Rain garden species: Botanical Name Apodasmia similis Astelia grandis Carex secta Carex testacea Carex virgata Cortaderia fulvida Carmichaelia williamsii Coprosma rigida Gahnia xanthocarpa Ficinia nodosa Hebe speciosa Leptospermum scoparium Lophomyrtus obcordata Machaerina sinclairii Phormium tenax Pseudopanax crassifolius
LANDFORM RAIN GARDEN DIAGRAM NATIVE PLANTING
RAIN GARDEN SOIL MIX OVERFLOW SYSTEM By simply adding rocks and boulders to the area, a secure habitat for lizards is created. It is important to increase the diversity of species as is it proportionally affects the quality of the ecosystem.
SPECIES TOLERANT OF FLOWS AND FREQUENT INUNDATION PONDING AREA
TALL GRASSES - FILTER CONTAMINANTS AND SLOWS DOWN FLOW AND REINFORCE SLOPES
Water uptake through roots enables plants to efficiently use the nutrients that are carried through the site. They also contribute towards the stability of the landform by supporting steeper areas.
TREES TO ESTABLISH ORGANIC MATTER AND SOIL POROSITY
This is the designated space for the rain garden. Running parallel to the road, it is the primary source of retaining and treating storm-water runoff. A native planting scheme is followed, as these types of vegetation are better suited for the climate condition. The reason for using a rain garden device is that is brings aesthetical qualities to the area and is considered a visual amenity. It creates a welcoming look, as well as contributing the ecological principles.