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InVEST Sediment Retention
Hands-on Session InVEST Sediment Retention NASA photo, not sure
where Erosion Increase maintenance cost Soil erosion and sediment
can cause:
Decrease in agricultural productivity Degradation of fish habitat
and aquatic life Water quality degradation Risk of structural
failures Increased dam maintenance costs Increase maintenance cost
Soil erosion can cause a lot of problems A healthy ecosystem can do
a lot to prevent these things from happening. Dense vegetation can
slow down and stop soil particles from eroding away, which helps
keep soil where we want it (like on farms) and keep it out of where
dont want it (like streams.), providing us with a valuable service.
Ecosystem Service questions
Where are the sediment sources? Where is sediment retained? How
much is retained? What is the value of this retention? In order to
quantify how an ecosystem helps mitigate erosion, we consider the
following questions InVEST Sediment Retention Model
Based on the Revised Universal Soil Loss Equation (RUSLE) Includes
geomorphology and climate Potential erosion on a parcel Enhanced by
hydraulic connectivity What happens as the parcels sediment moves
downslope? Influence of intervening landcover Sediment retention
valued asecosystem service For modeling sediment we provide a
Sediment Retention model.First the model determines how much
sediment will leave a parcel of land, using the Universal Soil Loss
Equation (USLE), which is a commonly-used method for estimating
potential erosion from a parcel. It includes both geomorphology and
climate.We make some modifications to the USLE to make it more
generally applicable, for example working with some Chinese
colleagues (Wang Yu Kuans group) to adjust the equation in terraced
areas. Once sediment leaves a parcel, it travels downslope until it
reaches a stream, so we also model how much of that sediment is
taken up by the vegetation that lies between the parcel and the
stream. The total amount of sediment retained by a parcel is valued
as the ecosystem service. InVEST Sediment Retention Model
Erosivity (R) Slope (LS) c Conservation Factor (P) To get more
specific, the USLE includes these factors: How steep the parcel is
(steep slopes will erode more easily); Rainfall erosivity (if
rainfall is intense, its more likely to cause erosion);
Conservation factor (whether erosion-reduction practices are done
on the land, like contour farming); Crop factor (how the vegetation
is managed, is tilling done); Soil erodibility (how susceptible the
soil is to eroding, based primarily on soil texture). All of these
are combined to give the potential erosion from each parcel on the
landscape. Soil Erodibility (K) Soil loss= R x K x LS x C x P Crop
factor (C) Hydraulic Connectivity
load (USLE) Flow direction Corn Forest export Wheat Forest
retention Once we know how much sediment leaves a parcel, we then
take into account what happens to it as it flows downslope until it
reaches a stream. In this example, sediment leaves a parcel of
corn, as it moves downslope the forest takes up some of it, and the
rest keeps moving to a parcel of wheat, which also takes up some of
it, as does another parcel of forest.Whatever does not get retained
by the intervening landscape enters the stream and is considered
export.The same thing happens with each parcel, and the final
retention value for a parcel of land is the sum of how much that
parcel retains from what comes to it from upstream. Stream to
reservoir Valuation Based on avoided treatment costs
Can value for dredging and/or water quality Time Loading Service
Critical Loading A reservoir can hold a certain amount of sediment
before it needs to be dredged.And a water treatment facility might
have a maximum amount of sediment that is allowed to remain in the
water that is delivered to its customers. We call both of these
critical loading.Since this amount does not need to be dredged or
treated, we do not include it in our valuation.The ecosystem
service value is based on the amount of sediment removed by the
landscape that is above the critical loading threshold, since thats
how much the facility would have to pay to remove otherwise.
Biophysical Outputs Potential Soil loss Sediment Retained
Calculated from USLE Per sub-watershed Sediment Retained Per
watershed and sub-watershed Used in valuation Three main outputs
are provided, all are per year.First is the potential soil loss,
which is the result of the USLE equation.Next is the actual soil
loss, how much of the potential erosion actually makes it to the
stream.And finally, the amount of sediment retained by the
landscape, which is the biophysical ecosystem service.Heres an
example of an output map, from a watershed in Colombia.The darker
green areas are where larger amounts of sediment are being
retained. Sediment retention Sediment Exported Per watershed and
sub-watershed High Low + Total export to reservoir
Assumptions/Limitations
Predicts erosion from sheet wash alone Sediment gets to outlet
within a year No limit to retention Accuracy limited in mountainous
areas Because the model is simple, it has some limitations Only
models sheet wash, no gully or bank erosion Future: Sediment
delivery ratio: the ratio of actual sediment load to gross erosion
estimated from USLE equation, is included in our model to account
for sediment export and retention processes at catchment scale
Takes into account for a catchment-specific parameter (proportional
to a particle size) and the travel time in the flow path. The
travel time through a single cell ( , ) is estimated from the ith
cell as a function of flow length ( , ) (m), vegetation roughness (
, ) and slope (%). The amount of sediment retained on a pixel is a
function of the amount of sediment inflow and the inverse of the
sediment delivery ratio on that pixel as well as the amount of
sediment retained on pixel due to crop and land management practice
Accuracy limited in mountainous areas limitation of USLE, we have
added functionality to do a better job, but its still not optimal
in very karsty or mountainous areas. Outlook Sediment delivery
ratio Gully and bank erosion Dam retention
Tier 2 sediment model West Coast East Coast Belize Colombia Mexico
Sediment delivery ratio: ratio of sediment yield of a drainage
basin to the total amount of sediment moved by sheet erosion and
channel erosion. The ratio of actual sediment load to gross erosion
estimated from USLE equation, is included in our model to account
for sediment export and retention processes at catchment scale. Dam
retention effect of sediment trapping in dams Multiflow algorithm
replacement for Arcs flow direction, instead ofonly one direction
for flow, can go in several directions. Ecuador Amazon Basin
Tanzania Indonesia Sediment retention in Colombia
Application Sediment retention in Colombia Dam 1 Dam 2 Supply Bogot
Service (dams) National analysis of ecosystem services in
Colombia.The supply of sediment retention is how much happens
whether we use it or not.Service is when people use it.Thus, when
we mapped the supply in Colombia, we could look at the whole
country.But when looking at service, we needed reservoirs or other
points where sediment retention is useful to us.We only had the
locations of a few major dams, so you see them here, along with the
sediment retained in the watersheds that flow to them. What I
wanted to point out here is what happens when several dams are
placed along a river.Their contributing watersheds are
overlapping.So any sediment retained at the top of the watershed
not only provides a service to the first dam, but also the others
downstream, since dams will only trap some sediment, and let some
continue downstream to the next dam.If we know the trapping rate,
then we can accurately calculate the service provided to subsequent
streams downstream.In this case we dont know, so we simply multiply
by the number of dams downstream. Scenarios for Mine Expansion in
Columbia
Current Mines Permits Granted Pending All possible permits Mining
in Columbia High Impact Zones should avoided Permits Granted
Permits Pending All possible Permits Hands-on Session Questions?
NASA photo, not sure where