Validating SEdiment Delivery Distributed (SEDD) model in a small Calabrian basin.

Validation of soil erosion and sediment yield models is very important in severalenvironmental contexts, such as the assessment of soil loss from agriculturallands and the estimation of water pollution risk for humans and aquatic ecosystems.In southern Italy, where soil loss associated with extreme rainfall events canreach annual values of 100 t ha-1, soil erosion has become a seriousenvironmental problem and there is a need to validate some theoretical modelsso that they can be used with confidence for predicting soil loss in differentcontexts.In this paper, the SEdiment Delivery Distributed model based on the USLEand the sediment delivery ratio of each morphological unit into which the basinis divided, is validated in a small basin (W2) located in Calabria (southern Italy).In previous contributions, the SEDD model was calibrated over the samebasin using 52 events for the recording period 1978-1994.The model is now applied at the event and annual scale using sediment yielddata collected during the period 2005-2007 at the basin outlet.In particular the median value of the specific parameter ?e,m, which wasestimated at the event scale with an inverse modelling approach during thecalibration phase is now introduced into the model and the calculated sedimentyield values, associated with the new events, have been compared with themeasured ones.The parameter ?e of each event was also estimated with an independentrelationship that relates ?e to runoff coefficient RCe at event scale. The reliabilityof the comparison between estimated and measured values of sediment yieldencourages the use of SEDD to predict sediment yield at the event scale in smallbasins.The validation of the SEDD model was also carried out at the annual scale. Inthis case, a median annual value of the specific parameter ?a,m was available.This median value, estimated in the previous analysis using the sediment yieldmeasurements carried out between 1978-1994, was used to calculate the totalsediment yield during the year 2006 and to compare it with the measured one.The same relationship between ?a and runoff coefficient RCa was applied at theannual scale in order to obtain a suitable estimate of the representative value of?a,m for long-term prediction of sediment yield.Using this approach, the parameter ?a,m was recalibrated using all availablemeasurements at an annual scale (1978-1994 and 2006) and allowed theapplication of the SEDD model at the mean annual scale to determine the spatialdistribution of the sediment yield into the basin.These estimates of sediment yield were compared with the rates of net soilloss provided by 137Cs measurements carried out in 1998 and 1999. The reasonableagreement between the two sets of sediment yield estimates confirmed theapplicability of the Sediment Delivery Distributed model if the specific parameter?a,m is calibrated using measured data.