It is now time to complete your first serious piece of design work - a design for a constructed wetland in the backyard of a detached dwelling.
You will have noticed that over recent years, local authorities (councils) in many cities have built what are called constructed wetlands, to manage flood waters and clean up polluted river systems. Wetlands contain many microscopic organisms such as algae and bacteria and form naturally in a wetland to create a bio-film over the surface of living and decaying plant materials. These organisms are very effective at breaking down pollutants in water (both stream and grey water from domestic housing) and turn them into nutrients that plants and microscopic animals can use, thereby improving water quality. The interrelated communities of plants and animals in wetlands improves and maintain water quality.
Tip: Ideally, constructed wetlands should be populated with bog plants that are native to the area. That will encourage native animals to set up home in the space. The wetland should be capable of retaining at least 7 days worth of water such that the water flowing into the final pool has been in contact with bio-films for that length of time.
Water use in homes - making a mini constructed wetland
Most waste water generated by households is not heavily polluted. Water from showers, bathtubs etc. is often called grey water and usually contains only small quantities of contaminates such as soaps and detergents. Australian households consume about 600 liters of water a day. About 1/3 of this is relatively clean grey water that can easily be treated with a 'constructed' backyard wetland. Moreover, a goodly proportion of this water can be recovered and used to water the remaining garden areas, so there is a real saving.
The table below shows a list of some drawing you may need to carry out the exercises here. Click to download and save to your Windows desktop.
|HouseDeckingDeciduous2||Finished wetland design - Exercise 1:|
|ConstructedWetlandAssembly||Base plan - Exercise 2|
|ImageFile||Image file for pasting into a gCADPlus design|
Examining a design for a small constructed wetland
Exercise 1: Examine a design for a small scale constructed wetland
Start gCADPlus by double clicking on the desktop icon and use File>Open and select the drawing HouseDeckingDeciduous2 (again).
Tip: To rapidly load a previously view drawing, click on the recent icon on the top toolbar.
Instead of looking this drawing from the point of view of learning to manipulate your view of a drawing as we did previously, focus on the design itself.
Use the wheel of the mouse to zoom in and focus on the wetland area. Follow the path of storm water from the tank under the deck to the final pond. If you need to pan the drawing, hold the mouse key down and drag.
Right click and select zoom extents.
Return to model space if you happened to have click the a layout space (view).
Select Tools> Distance and use the distance command to measure the distance from the deck to the back boundary.
Measure the distance across the site.
Make sure that you understand the drawing is a full size model.
Can you use the Area tool (under the Tools drop down menu) to estimate the total area of the wetland?
Note that you need to convert from sq mm to sq m?
Design your own backyard wetland
Here is a movie showing how to design a constructed wetland for a backyard using GardenCAD Plus. In the exercise that follows, you will make your own design. We hope to show show how easy it is to create your own designs for a constructed wetland using the GardenCAD Plus template and drag/drop/copy features. the movie is quite detailed and we expect that you may need to run it several times.
Exercise 2: Design your own backyard wetland to treat grey water
The figure below shows the drawing as you should see it.
The symbols on the right can be used to make a landscape design by dragging them into position.
As shown in the movie, left click on a symbol to select it, left click again on the center block (handle)and move the symbol to a new position.
Drag more symbols into place as shown in the movie to complete your design.
Make sure that you include a north point indicator.
We are sure that you will be able to make a better design than our. Our design was completed in 10 minutes and we made the movie complete with mistakes) as we were doing so.
By way of revision, you might try printing the design to a PDF file. To do that follow the File>SaveAs PDF. It is possible to select the resolution and area of the design that will be incorporated into the design.
Adding some images to the design
A picture is worth a thousand words. Because GardenCAD Plus allows designers to convey design ideas by putting pictures into a design, you can dramatically cut drafting time using well chosen images. You might for example want to create a new layout sheet and populate it with images of the plants and animals found in a wetland or even some garden art to 'spice up' the design.
Add images to the wetland drawing
Download a suitable image from the images tab at www.plantdatabase.gardencad.net. Save it to the desktop.
Move to the wetland tab.
Select Draw>Raster Image
Find the image from your desktop.
Insert the image.
It is really important at this stage to recognize that our design models the real world. Lengths must be entered accurately. That's the topic for the next module, but before you move on, please play the movie below.
Remove boundary lines, check length
Open the HouseDeckingDeciduous drawing again.
As shown in the movie, erase the magenta boundary lines and put some new boundary lines in place.
Select one of these and check its length using the Properties box.
The next module "Making accurate base plans" shows how important it is to measure a site accurately before laying out a design.
Here is some extra information that expands the discussion in this module.
(1) SppDb - the personal plant database (free version available).
SppDb has been created specifically for landscape designers and is a tool for storing comprehensive and detailed information about the characteristics of individual plant species that you actually work with. In essence, the software enables the creation of a searchable, personal plant file. Use it to load your own information about familiar plants and refine it as you gain more experience. The image below shows a typical record in SppDb and shows detail about one of the Banksia species. Note that the path to the image file is stored. This means that you can copy that path and easily insert the file into a gCADPlus drawing sheet.
(2) Here is some more background information on constructed wetlands.
Wetlands play an important role in managing water in urban catchment areas. The figure below shows a generic design for a constructed wetland.
Vegetation within the wetland can be broken up into zones perpendicular to the flow. These zones refer to the depth of water and appropriate species to be selected to optimize the success of the system. All species used in vegetation, including both aquatic and terrestrial, should be indigenous and local provenance. In areas of predictable low rainfall patterns and where there is also a high evaporative loss due to wind sheer, the wetland should use a vegetation sequence such that there is sustainable water depths in deep and submerged marsh areas during drawn down, as illustrated below.
Constructed wetlands can be small scale. A wetland has been constructed at Urrbrae Agricultural School in Adelaide, South Australia to treat effluent water from a nursery. Water used to irrigate plants in pots and trays collects considerable nutrient. A small wetland can deal with this waste; although the design is somewhat different to the above, the principles are the same. In winter, the growth in the wetland can be harvested and returned to the mulching heap.
The inlet tank
Inlet outflow spreader and Stage 1 plants (knobby club rush and sedges).
Stage 2 plants - Marsilea spp - Nardoo. Used by indigenous Australians to make bread.This photograph was taken in summer when growth in the wetland is at its peak. Contrast this with the last figure below which was taken in winter.
The figure below shows the wetland in late winter, immediately after the harvest of plants. It is now ready for a new season.