The sed-export is calculated with the SDR-approach.
SDR = function of:
watershed area (km2)
relief ratio (m/km) (average divide height vs. river valley length)
curve number value (Average for watershed)
it seams it does not matter how far away (1m or 10km) from the actual stream a heavily erodible agriculture parcel is for the sed-export calculations. In other words: a pixel or a parcel in the same catchment will have the same impact very next to a river (the stream) or 10 km far away. Am i wrong?
The InVEST SDR model does not use curve number. Sediment export is a function of the area upslope of each pixel, the slope both upslope and downslope of each pixel, and the landcover characteristics (USLE C) both upslope and downslope. You can read about this in more detail in the User Guide.
It does matter how far from the stream a parcel is for calculating sediment export. The SDR equation includes the length of the downslope path between the pixel and the stream (See Equation 5 in the User Guide.) So pixels that are further away are more likely to have their erosion retained before reaching the stream, depending on what kind of vegetation is along that downslope path.