Last Thursday I went for a drive with Rowena to check on the progress of conditions at Gooseneck Swamp – Day 17 of the restoration trial. When I got home later that evening, I discovered in an email from Rod Bird (of the Hamilton Field Naturalists) that he also had the same idea, having visited the site a day earlier on Wednesday 11th September 2013.
This was handy, as it has given us the opportunity to momentarily review how water levels were changing on a daily basis…
The receding water levels indicate a few things that are very helpful for our developing understanding of the hydrology of the site.
- The sandbag weir effectively retained the peak inflows into Gooseneck Swamp (at least those that arrived after the construction of the structure on the 26th August) as a result of the August rainfall events in the local catchment.
- Based on an observation made by the neighbour during the first week of the trial, levels may have peaked at around 75 cm at our gauge-board prior to beginning to recede as inflows have dropped.
- Peak levels were very close to over-topping the current maximum height of the sand-bag weir structure, noting that its current sill height is well below the full bank height of the lunette feature the drain cutting passes through – and giving us more flexibility to raise its height if required.
- The natural flowpath between Gooseneck Swamp and Brady Swamp (the eastern-most and most defined distributary of the Wannon River delta that feeds Brady Swamp) is effectively carrying all flows from Gooseneck swamp at its current re-instated level, and those flows (although still significant) have dropped noticeably since Day 7, corresponding with the receding levels in Gooseneck Swamp.
- The effect of the sandbag weir structure on static inundation levels and duration will become most apparent when (assuming for a moment that no further major inflows are received this spring) swamp levels drop to the point where the natural overflow ceases to discharge into Brady Swamp.
We certainly have some interesting months ahead, particularly as the ecological impacts of the trial begin to unfold during the spring!