Abdallah House - Redesigning a Home: Wetland works

Saturday, December 12, 2009

Wetland works

Principle 7: Design from patterns to details

The concept of catching and storing water in the front yard wetland worked well from the start, but it needed some fine tuning. When the rains came back to fill up the depression I could see where high and low points were, so I leveled them out. Having a level area gives the water a greater surface area to soak into the ground. Ideally the water would soak in within 12 hours.

Wetland tinkering, leveling out and building up / defining edges

Wetland during downpour

Water run-off from laneway entering wetland and overflowing

The water took longer than anticipated to soak into the ground, about a week. I think that it was taking a long time because the soil was in poor condition and compacted. As the life comes back to the soil I would expect quicker water infiltration.

One of the problems when water takes so long to soak in is that mosquitos get a chance to breed. Adult mossies take 5-14 days to emerge (depending on the species & temperature). We had heavy rains, followed by more heavy rains a few days later, which meant that the water didn't get a chance to soak in and the breeding time for mossies increased.

Mossies larvae in stagnant water after nine days, just begining to emerge as adults

Wetland drying out, just in time

Fortunately the water soaked in before the adults emerged. I bought two and a half cubic metres of locally sourced mulch and spread it out over the surface. This gave about a 50-75mm cover, which is enough to prevent water stagnating, and mossies breeding. Logs were added to provide a visual barrier, some shelter for plants and habitat for critters.

I blocked the inlet channel from the laneway with some minor earthworks to give the wetland a chance to dry out a bit. This is easily reversed if I want to bring more water in (and it rains). Extra soil was added to define the edge of the channel and stones used within it to reduce the boggyness.