1. InVEST Sediment Retention
Hands-on Session
InVEST
Sediment
Retention
NASA photo, not sure where

2. 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 don’t want it (like streams.), providing us with a valuable service.

3. 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…

4. 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 parcel’s sediment moves downslope?
Influence of intervening landcover
Sediment retention valued as ecosystem 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 Kuan’s 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.

5. 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, it’s 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)

6. 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

7. 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 that’s how much the facility would have to pay to remove otherwise.

8. 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. Here’s 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

9. 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 𝛾 (proportional to a particle size) and the travel time in the flow path. The travel time through a single cell ( 𝑡 𝑖,𝑗 ) is estimated from the ith cell as a function of flow length ( 𝑙 𝑖,𝑗 ) (m), vegetation roughness ( 𝛼 𝑖,𝑗 ) 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 it’s still not optimal in very karsty or mountainous areas.

10. 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 Arc’s flow direction, instead of only one direction for flow, can go in several directions.
Ecuador
Amazon Basin
Tanzania
Indonesia

11. Sediment retention in Colombia
Application
Sediment retention in Colombia
Dam 1
Dam 2
Supply
Bogotá
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 don’t know, so we simply multiply by the number of dams downstream.

12. Scenarios for Mine Expansion in Columbia
Current
Mines
Permits
Granted
Pending
All possible
permits

13. Mining in Columbia High Impact Zones should avoided Permits Granted
Permits Pending
All possible Permits

14. Hands-on Session
Questions?
NASA photo, not sure where