The Making of the Wetland
The idea of creating a wetland came on us slowly. When at Snake Valley, we have a pattern of walking around the boundary a couple of times a day. Our block undulates in a gentle sort of way and over the years we have observed the patterns of water flow during winter when parts become quite boggy. Occasionally there is a steady flow of water, only centimetres deep but up to 10 metres across flowing across the bottom paddock. There was one obvious point at which most water flowing across our land found its way under a fence and into the next property. "Why don't we put a small bank there, let the water back up when it flows and make a little wetland?" was the idle thought one day. Well, one thing led to another and over the space of about 18 months the idea firmed up and we decided to get a quote or two.
Once we were clear that we really were serious we started reading quite a bit about wetlands. Two highly recommended books, that are now in our library, are:
As our thinking evolved we arranged for visits by a few individuals from the Department of Natural Resources and Environment and LandCare. These people were very supportive of our plans and gave encouragement both in terms of recognising the site as a suitable one for a wetland and encouraging this type of land use. Much earlier we had also had our property approved as a Land for Wildlife property.
We contacted a couple of earthmoving firms and arranged site inspections and quotations. Midwest Earthmovers who ultimately got the job, brought a laser level and taking into account the undulations in our site, marked out the rough boundaries of the site. Our little bank of maybe 10 metres in length had become a bank over 100 metres in length. Despite this being a much larger scale operation than we anticipated, it was obvious that it was necessary in order to join two matching high points. And admittedly, the prospect of a good sized wetland (2-3 acres) soon grabbed us.
Having marked out the rough high water points, Midwest provided us with a sketch to use when seeking permits and relevant permissions. (View Midwest sketch.)
Within the rough boundaries indicated in their plan we also began planning islands and edges. Uneven edges are good so as far as was practical we tried to build these in.
There was quite a delay, about 10 months, between getting the quote and starting work. This was mainly due to the need to do the work during the dry post-Christmas period but it also gave us time to check out the situation concerning permits and legal requirements and to do more research about wetlands.
Submission to BOCA
During this time we also applied for some funding from the Australian Bird Environment Foundation (ABEF) through the Bird Observers' Club of Australia (BOCA) to assist in the costs of creating the wetland. Our submission was unsuccessful as they did not provide funding to create new wetlands, only to renovate or improve existing wetlands. This wasn't clear from the funding guidelines but the work we had to do in preparing the submission wasn't really wasted as it caused us to focus our thinking and to document the presence of plants and animals on our land. We are fortunate enough to have a friend who enjoys flying (thanks, John!) so we were able to get some aerial shots both before and after the earthworks were undertaken. For the submission, I overlaid my best guess of where the wetland would be. No-one could have been more suprised than me when the actual result ended up so close!
Permits, Permissions and Legal Stuff
We were very cautious about making sure that we had appropriate permissions before starting work. Ultimately it came down to meeting whatever requirements our Water Management and Local Government bodies had. The Water Authority advised us that no permits were necessary as we weren't blocking a defined waterway. The Council also advised, (we made sure we got this in writing), that no permits were necessary. It was of significance to the Council that we had been discussing our plans with staff from the Department of Natural Resources and Environment.
The Basic Design
A very important element of wetlands is an area of shallow, gently sloping ground. This allows for natural fluctuations in water level, accommodates a range of plants that require different depths of water, supports wading water birds and birds that require deeper water, and allows for some areas to undergo a flood and drying out cycle. Our basic plan of building a retaining wall across a low point, thus forcing water to flood back up over gently sloping ground was sound.
Now that we knew the basic size of the total flood area we could start playing around with ideas for islands and shaping the edges. An island was big on our plans to provide a relatively secure place for birds to breed. (And, ya gotta agree, there's something nice about the idea of islands!)
We arrived at a basic design which inevitably underwent modification once work began. The following sketch is pretty much the last version, created about half way through the actual work. Practicalities, such as the limits of a bulldozer's working radius, determined some of the final features but the sketch here contains the essential elements that we ended up with. (View Di's final sketch.)
It was a big day when we heard the bulldozer being unloaded from the low-loader at the end of the track - January 16 2001. We felt a mixture of excitement and trepidation as the bulldozer squeezed itself through our gate and began trundling down the paddock to the site of the proposed wetland.
Once the bulldozer was on site more detailed surveying was the first step. Rob Lakey, the Midwest manager, and Clint Crimeen, the bulldozer operater, marked out the site in more detail. They identified the line of the bank and the overall flood area was marked out.
The first stage was to push all the topsoil from the area of the wall away behind the line of the proposed wall. This meant that when the wall was completed the topsoil could be pushed back and over the wall again relatively easily.
The topsoil from the flood area, the shallow part, would be pushed away to each side from where it could be carted away. We had decided to sell the bulk of the topsoil to offset the cost of the construction work. Subsoil was to be left over the area that would be flooded so we would not have large exposed clay areas. This was to encourage plant growth and to keep the water relatively clean by avoiding colloidal clay.
Clearing the topsoil took about a day and a half.
Forming the Bank
Once the topsoil was cleared the serious work of forming the bank began. This was a very steady process of pushing up the clay from the borrow area, forming the wall and compacting it with the bulldozer.
The borrow area is the area in front of the bank from which clay is taken to form the wall. This becomes quite a deep area as all the clay from which the wall is formed has to come out of it. The larger the bank, the more clay has to be taken from the borrow area. In the case of our wetland, unlike a storage dam where a regular shaped hollow of fairly even depth is constructed, we wanted most of the clay to be taken from immediately in front of the bank, leaving a gentle and shallow slope over the rest of the wetland. As a result we have a 5 metre deep area right along the foot of the wall, 2 metre channels around the islands, and then a large area varying between about a metre and a few centimetres over about 70% of the total flood area.
Forming the Islands and Promontory
As the bank neared completion the islands had to be considered. Broadly speaking, the islands were formed by cutting channels around the areas defined as future islands. Once this was done, clay was added to their tops to raise the levels to the same height as the bank top. The high water mark for the bank and the island tops was .6 of a metre (around 2 feet) below the top. A similar process was followed in creating the promontory. All of these structures have relatively gentle gradients on their edges. This is so water levels change gradually and birds can move in and out with minimal difficulty. The last stage of island development was to push topsoil over the islands.
Finishing off involved some final smoothing and evening up and spreading topsoil everywhere it was needed.
The job in total took six days of 9 hours with the bulldozer working almost constantly over that time. The whole job was done with just the single bulldozer and no other machinery.
This account is being written 18 months after the wetland was constructed and at the end of its second winter and we've had a bit of time to reflect on our experiences.
Liaison with the Contracters
We can't stress too highly how important it is to have contractors who respect what you are doing and who welcome your input as the project evolves. Unlike a formal engineering project, you may not have detailed drawings so it's all the more important that your contractors accommodate your (changing) plans. We were very fortunate as MidWest went out of their way to seek our input each day and were very receptive to changes we wanted along the way. It's very difficult to visualise a project like this and as it takes form in front of you some ideas will go out the window and others will come in the door.
It is also possible to get a bit anxious about the cost as the job goes on. Keep in mind that the extra cost will soon be forgotten once the job's finished but you may always regret not having that second island added or the extra bit of topsoil spread. That wetland's going to be around a long time!
We were able to sell around 1200 cubic metres of topsoil. This returned just a little under half the cost of building the wetland. Given that we hadn't thought of selling our topsoil when we originally budgeted for the work this was a great outcome. We still have around 800 cubic metres to use as we see fit. Any concerns we had about selling the topsoil have disappeared. Leaving subsoil in place and replacing topsoil in exposed areas has been completely successful. The water is surprising clean, even without extensive wetland plants yet.
Some excellent advice we were given was to get the topsoil sale signed up early and insist on early removal. We've heard horror stories of topsoil being carted away after the start of the autumn rains, resulting in badly damaged paddocks. The soil that was removed required 60 truck/trailer loads and if this had occurred on soft tracks the damage would have been enormous. Early removal also meant access to the soil was easy and the site could begin regenerating immediately without trucks and loaders running over new growth.
We're very fortunate to have excellent catchment. Our wetland is the lowest point of an area probably in excess of 60-80 acres so once water starts flowing most ends up in our wetland. This has mixed benefits. We haven't had the variation in levels yet that we anticipated and it seems that it's going to be fairly full for most of the time. A concern is that most of that catchment is on a neighbour's property and hence our water supply is subject to his land use. At present he only grazes cattle but anything more intensive or the use of farm chemicals would almost certainly affect the water flowing into our wetland. Water does have to flow about 100 metres across our grassland before entering the wetland so that would have some filtering effect. This does result in the water flowing in being free of clay and soil deposits.
This site developed and maintained by Ian Wright.
Last updated on Monday, June 18, 2012 07:16PM.