Testing the Ephemeral Gully Erosion Model (EGEM) for two Mediterranean environments

Abstract

Few models can predict ephemeral gully erosion rates (e.g. CREAMS, EGEM). The Ephemeral Gully Erosion Model (EGEM) was specifically developed to predict soil loss by ephemeral gully erosion. Although EGEM claims to have a great potential in predicting soil losses by ephemeral gully erosion, it has never been thoroughly tested. The objective of this study was to evaluate the suitability of EGEM for predicting ephemeral gully erosion rates in Mediterranean environments. An EGEM-input data set for 86 ephemeral gullies was collected: detailed measurements of 46 ephemeral gullies were made in intensively cultivated land and abandoned land in southeast Spain (Guadalentin study area) and another 40 ephermal gyllies were measured in both intensively cultivated land and abandoned land in southeast Portugal (Alentejo study area). Together with the assessment of all EGEM-input parameters, the actual eroded volume for each ephermal gully was also determined in the field. A very good relationship between predicted and measured ephermal gully volumes was found (R2 = 0.88). But as ephermal gully length is an EGEM input parameter, both predicted and measured ephermal gully volumes have to be divided by this ephermal gully length in order to test the predictive capability of EGEM. The resulting relationship between predicted and measured ephemeral gully cross-sections is rather weak (R2=0.27). Therefore it can be concluded that EGEM is not capable of predicting ephermal gully erosion for the the given Mediterranean areas. A second conclusion is that ephermal gully length is a key parameter in determining the ephermal gully volume. Regression analysis shows that a very significant relation between ephermal gully length is therefore crucial for assessing ephermal gully erosion rates.