Anyone have any quick methods, or references to methods, for quantifying sediment export from tidal wetland sediment surfaces (surface erosion) that would give some useful numbers over a period of 10 days?
Update:
Thanks for the responses so far. To give some clearer context.. this is a project working with Traditional Owners in a very remote area of Northern Australia. The salt flats are heavily impacted by cattle and 4WD vehicles (see attached photos for context). These impacts threaten resilience to sea level rise and we suspect, increase sediment export to nearby marine habitats. The Traditional Owners are working to reduce these impacts, so we're assisting with developing some straight-forward low-cost monitoring techniques that could be used to justify their actions in terms of reducing sediment runoff to the adjacent Great Barrier Reef Marine Park. There is LiDAR in places along transects only. But specifically the questions are 1. Does vehicle and cattle damage increase sediment export and reduce sediment trapping capacity of salt marsh and salt flats (and by how much)? 2. Does reducing vehicle and cattle impacts reduce sediment export from previously damaged areas (or is intervention required to improve tidal wetland health)?. We'll be employing an mBACI design to test this, with sites established in impacted and unimpacted areas (20x20m plots). In each site we'll look at sediment deposition rates (filter paper traps and tubes, feldspar), algal mat cover and density, veg cover, but the surface sediment loss is something that I struggle to find cheap ways of measuring without first having to disturb the sediment (ie. sediment plates). The scour chains are a good long-term strategy but possibly achieve the same result as an array of sediment pins. I'm wondering if some cheap turbidity probes might suffice (incoming v outgoing tide turbidity). All comments welcome. Thanks. (see also photo attached in answers below)
This is not my exact expertise so My concern is eyou have identified a very complex subject with potential for combination of freshwater and sediment inputs as well as erosion, tidal and associated sediment inflow and outflow, periods of potential sediment accumulation (aggradation or negative erosion) from upland sources during periods of tidalwedge acting more or less as a temporary dam to slow velocity and store sediment.
I believe better to find another subject as quick (ten days) is just not enough time to do your subject justice. 90 percent of sediment movement in streams commonly occurs in just 5-10 percent of the time. It would be difficult to assume any ten day period of s year to be representive, and there is likely to be year to year variability. Sediment transport as well as storage is also specific to the circumstances. A full literature search and several years time, may be able to help you tackle a complex subject like this, and I may have some ideas on methods that take time and repeated measures to quantify the complexities in time, space, events.
Tools such as radar for bathymetry, LiDAR for exposed surfaces may be useful, but snapshots best over a much longer time span. If you can find some survey data from years past, perhaps recreating the survey might allow you to analyze for change detection and get closer to where you want to be.
These authors may be willing to offer access to their model, as well as information or assistance in getting a rapid assessment, based on their experience.
You might consider using "scour chains" to measure sediment erosion using "scour chains". These simple devices consisted of a short length of plastic chain, with a cork float at the top end, and and anchor plate at the bottom. The chain is buried vertically, and the amount of erosion is indicated by the number of the lengths that become exposed. This is a standard method of the U.S. Department of Agriculture/Forest Service, I am attaching a PDF that gives the details of the method.
Best wishes,
George
Thanks for the responses so far. To give some clearer context.. this is a project working with Traditional Owners in a very remote area of Northern Australia. The salt flats are heavily impacted by cattle and 4WD vehicles (see attached photos for context). These impacts threaten resilience to sea level rise and we suspect, increase sediment export to nearby marine habitats. The Traditional Owners are working to reduce these impacts, so we're assisting with developing some straight-forward low-cost monitoring techniques that could be used to justify their actions in terms of reducing sediment runoff to the adjacent Great Barrier Reef Marine Park. There is LiDAR in places. But specifically the questions are 1. Does vehicle and cattle damage increase sediment export and reduce sediment trapping capacity of salt marsh and salt flats (and by how much)? 2. Does reducing vehicle and cattle impacts reduce sediment export from previously damaged areas (or is intervention required to improve tidal wetland health)?. We'll be employing an mBACI design to test this, with sites established in impacted and unimpacted areas (20x20m plots). In each site we'll look at sediment deposition rates (filter paper traps and tubes, feldspar), algal mat cover and density, veg cover, but the surface sediment loss is something that I struggle to find cheap ways of measuring without first having to disturb the sediment (ie. sediment plates). The scour chains are a good long-term strategy but possibly achieve the same result as an array of sediment pins. I'm wondering if some cheap turbidity probes might suffice (incoming v outgoing tide turbidity). All comments welcome. Thanks.
If you are familiar with the filter fabric fences we used in the small gully measurement of sediment (research gate about 2007)
, I would make something as small as a D net (used to sample aquatics), or make aquatic insect drift nets out of filter fabric with 1 m x 1m opening, or even larger to width of a ATV tread as desired. The filter fabric net would capture the sediment, and could probably be weighed with the first two type of nets, or volumetric measured with last larger sediment fence. I have some ideas how these may be installed to allow the free landward tidal cycle and raise the fence at high tide to capture the seaward erosion as it declines. But if you look at the use of the filter fabric fencing approach, it could be adjusted in a number of ways to capture a sample of sediment from below various surfaces and disturbances, inexpensive, fast to install, but can take time to measure sediment if you want accuracy. The fabric fence dams do not necessarily need to be straight across, and could curve if needed, and reduce the height if only catching one tidal cycle.
I have used these to measure fire erosion and sediment delivery effects an have used on fireline effects, somewhat larger than ATV dimensions. I think I explained well enough in the gully sediment paper, but OK if you want to contact me. If you can define small coastal catchments, this could assess sediment from larger areas, but some disturbance is needed to embed the fence in the surface .
Maybe the SediMeter could be used. It depends on the setting, if you could find a good spot where to measure. The screen capture is from a reservoir in Zambia, it shows that the instrument detected what is probably gas in the sediments, that was later dissolved when a rainstorm lowered the temperature (green line, left scale in ºC), then the turbidity increased (blue line, right scale in FBU), then the bottom level increased (black line, left scale in cm). I enclose a link to another deployment, on that site you can find more information about the instrument.
http://lindorm.com/rd/sm1.php
Sorry to not read through all the above but if you have some ground control and water is not hindering your view you might want to check out close range remote sensing (SfM: https://www.researchgate.net/publication/286932350_Image-based_surface_reconstruction_in_geomorphometry_-_merits_limits_and_developments)
In case of questions just contact me directly if you are unsure about how to do a survery. Its efficient, precise and fun!
Article Image-based surface reconstruction in geomorphometry - merit...
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