Under a defined experimental conditions sediment loss can be well categorized  for a particular soil type. Please refer some papers of Pathak et al in Agricultural Water Management Journal published in recent years from ICRISAT, Patancheru.

Permissible soil erosion is defined in such a way that soil formation "in situ" balances out soil losses due to erosion. Soil formation rates in that sense are taken as a rough average, wich in my opinion, should be reviewed thoroughly and presented according to local conditions (wet, dry climate, topography, and the list of factors to consider goes on).

Sediment loss in a watershed (more commonly treated as sediment yield) is the net result of a erosion and sedimentation processes among or across different landforms. For example soil particles eroding from a slope will be deposited on flatter landforms below the slope. In this sense, erosion from the slope becomes a soil forming factor for the flatter terrain below !!! For this particles to become part of the sediment yield, they need to be re-detached, removed, enter the stream and kept in motion. Supposing that the slope has no net soil loss (erosion and soil formation are equal) and that the processes mentioned above for the flatter terrain ocurr at a lower rate (than the erosion on the slope) there will actually be a positive balance of soil formation in the flatter terrain, while stil delivering sediment at the watershed outlet. In summary: sediment yield tells us "how much material of any kind" is comming out of the watershed, but not how much soil is being lost.

"Permissible erosion" immplies that human beings are "interested" in mantaining certain soil ammount within a given area. Could there be some interest in mantaining material within a watershed even if soil has a positive nett balance? I doubt it, if not for landscape reasons.

One more thing to take into account is that allthough there may exist some correlation between soil erosion rates and sediment yield, there is no straight forward physicall relation for these, as may be deduced from the example above.

To summarize:

Permissible erosion immplies a series of concepts and processes that cannot be equated to some form of "permissible sediment yield". These means that it would not make sense to define such a parameter.

In any case what are you trying to do? What is your objective?

Thank Dr Anleu for the detailed  and informative response.

As you mentioned  "there is no straight forward physical relation between soil erosion and sediment yield", my concern is what is the threshold value of the sediment yield that can be considered as permissible limit of sediment yield?

There is a body of literature that puts forth a general limit of 11.2 Mg ha−1 yr−1 as permissible limit for soil erosion. Is there any such general limit for sediment yield from watershed? My objective is to know whether the sediment yield, that i have estimated for two watersheds in eastern plateau region of India, is within permissible limits.

Or is it that we have to define such limits after carrying out some assessments for the individual watersheds. If yes, what analysis/assessment is required to define such limits?

Many Thanks

Maybe what I wrote was a little confusing. In short you cannot define something like a permisible limit for sediment yield. There is no theorethical reasoning that can support this, because sediment yield does not immply loosing any resource. It is possible to have net soild build up and stil have sediment yield from the watershed.

You can try sediment delivery ratio (SDR) approach. It is a ratio between sediment yield and total erosion of catchment area. Based on my field experience, if the value of SDR less than 50%, its means normal. However, we should be consider about biophysic characteristic such as soil, surface morphology, riverbank morfometric etc.

As such there is no universal limit for permissible soil loss. Many researchers have quoted different range of soil erosion as low, medium, high, severe and very severe.

In Central India, the normal watershed yield in the range of 10-15 t/ha/yr.

Oliveira et al. (2008) and Derpsch et al. (1986) obtained mean values for soil loss tolerance in Oxisols of 10.64 and 12 t ha-1 y-1respectively.

Derpsch, R., Sidiras, N., Roth, C.H., 1986. Results of studies made from 1977 to 1984 control erosion by cover crops and no-tillage techniques in Paraná, Brazil. Soil Till. Res. 8, 253–263.

Oliveira, F.P., Santos, D., Silva, I.F., Silva, M.L.N., 2008. Tolerance for soil loss by

erosion in Paraíba State. Rev. Bio. Ci. da Terra 8 (2), 60–71 (in Portuguese).

Observe that these values are for Oxisols. Different classes of soils will have diverse values. Soil conservation is a complex issue and sediment yield must take into account the watershed as a whole. Geomorphology research is fundamental. 

In my research in the mountain region of Rio de Janeiro, sediment yield was            14.8 t ha-1 in the period of March 2008 to January 2009 in an Oxisol.

Nacinovic, M.G.G., Mahler, C.F., Avelar, A.S., 2014. Soil erosion as a function of different agricultural land use in Rio de Janeiro. Soil Till. Res. 144, 164-173.

 Mendes et al. (2011), in a study with erosion plots, observed a sediment yield of  30 t ha-1y-1 in an olericulture parcel in a mountain area of Rio de Janeiro state.

Mendes, C.A.R., Mahler, C.F., Andrade, A.G., 2011. Superficial erosion in a yellow

argisol under perennial crop and fallow forest in a mountainous area. R. Bras. Ci.

Solo 35, 1387–1396 (in Portuguese).

Four thousand lives were lost in floods and landslides in 2011 in the mountain region of Rio de Janeiro State - in particular in the cities of Teresópolis and Nova Friburgo. Erosion is causing siltation of the major rivers in this region which potentializes floods. This fact is not permissible!

Refering to the answer from Idung I just like to say word of caution. The SDR is in did an interesting index, but can only be interpreted in terms of its magnitude and be used to compare different regions, but not against a "permissible limit".

This is a great question I have grappled with for a number of years. The USLE T value is based on the estimated rate of sediment regeneration. It has since been modified to allow farmers to continue to grow crops in some areas where erosion was particularly high. In the sediment yield context, things become much more "murky"! I have seen several approaches. A common approach is to define the "beneficial uses" of the water downs stream, and then determine whether there is a threshold of sedimentation that will offset the beneficial use. I do not like this method, as sometimes the beneficial use is something that was never a a part of that system. I prefer to estimate a natural background rate, and then develop methods to keep long term sedimentation averages within that rate. In watersheds that were traditionally forested or grasslands, that long term sedimentation must include sediment delivery following occasional wildfires. In mountainous watersheds, that long term average rate must include sediment delivered by mass wastage in very wet years. I have discussed this idea in a recent paper

In view of the preceding discussions, we can say that there is no universal threshold value of the permissible sediment loss from the watershed.  Dr Rafael Anleu highlighted an important issue that soil particles eroded from a particular plot in the watershed may not find its way to the watershed outlet because of obvious deposition at other places. Any of the two approaches, as suggested by Dr William, preferably the second one, can be applied to estimate the permissible limits of sediment yield. The concept of SDR can only be used to get the sediment loss from the watershed and is not useful in defining permissible limits in true sense.  I request Dr William to kindly forward the copy the paper in which the idea of permissible sediment loss is discussed.

Thank you all for the sparing time on this interesting issue.

i agree with Rafael Anleu

It is a good thing to share these valuable comments.

yes abbas really its valuable comments