 My name is Perin Hamel, I'm a hydrologist at the Natural Capital Project and in this video I'm going to present the invest sediment retention model. So the model is very similar to the nutrient retention model so if you're familiar with the latter you may find the concept and approach is very similar. So like most invest models the sediment retention model can be best described within the ecosystem services framework, supply, service and value like at the bottom of the slide here. Starting with the end the value one can ask what are the benefits of sediment retention and obviously they are very contextual but often people are interested in the improvement in water quality to avoid or minimize treatment or the dredging in case of a reservoir. So going backwards the service of interest is water purification and the service is supplied by the natural vegetation so depending on the location with regard to the stream or to main sources of sediment the natural vegetation is going to retain more sediment. The approach taken in the model has two components first the model computes soil loss based on the universal soil loss equation or USLE. Moving clockwise on this slide this approach considers the erosivity of the rain so the the rain intensity and the practice and cover factors which depends on the land use land cover and the soil erodibility so the the potential for a given soil to actually erode with rain and then the the slope of the particular area. So in a second step the model will compute the transport capacity on each cell so to do this we first consider the upslope component which looks at the the flow or amount of energy available to transport the sediment downstream and then there's the downslope flow path so this represents the the potential for the sediment to be retained before it reaches the stream so this depends on the distance and slope and retention capacity of the land use land cover on the way to the stream so for example if there are more vegetated areas the more sediment is likely to be trapped than in for best or for example. So such a simple representation of the sediment dynamics implies that there are limitations and the main one in my view is that the model only considers a sheet wash erosion so other sediment sources coming from landslides mass erosion are not considered so if this these are significant processes in the in the landscape it needs to be taken into account. Second the model is not a design tool it's not looking at extreme events but rather it computes long-term annual average sediment loads and finally the model requires calibration data to improve quantitative predictions so this is not unique to the model there's still there's still major knowledge gaps in the science and so this needs to be taken into account when looking at the valuation steps. Moving on to the inputs to run the model the users will need information about climate and soil so these aero zivity and aero debility factors that we've seen before the land use land cover and its spatial distribution the watersheds so these areas that drain to to a single point in the landscape the topography so the digital elevation model or DEM and then socio-economic data to inform the the valuation step so with these inputs the the model will produce the potential soil loss or the amount of eroded material in the landscape the sediment exported and retained on each sub-watershed and then the value of sediment retention either in terms of avoided treatment or dredging so as a summary we can go back to the overview slide and see how the sediment retention computed by the biophysical part of the model can be used to inform the service and benefits provided by different parts of the landscape so this helps understand how much sediment is retained and where in the landscape which can be compared with other ecosystem services to inform the decision process