CRHyME (Climatic Rainfall Hydrogeological Modelling Experiment): a new model for geo-hydrological hazard assessment at the basin scale

Abstract

Abstract. This work presents the new model called CRHyME (Climatic Rainfall Hydrogeological Modelling Experiment), a tool for geo-hydrological hazard evaluation. CRHyME is a physically based and spatially distributed model written in the Python language that represents an extension of the classic hydrological models working at the basin scale. CRHyME's main focus consists of simulating rainfall-induced geo-hydrological instabilities such as shallow landslides, debris flows, catchment erosion and sediment transport into a river. These phenomena are conventionally decoupled from a hydrological routine, while in CRHyME they are simultaneously and quantitatively evaluated within the same code through a multi-hazard approach. CRHyME is applied within some case studies across northern Italy. Among these, the Caldone catchment, a well-monitored basin of 27 km2 located near the city of Lecco (Lombardy), was considered for the calibration of solid-transport routine testing, as well as the spatial-scale dependence related to digital terrain resolution. CRHyME was applied across larger basins of the Valtellina (Alps) and Emilia (Apennines) areas (∼2600 km2) which have experienced severe geo-hydrological episodes triggered by heavy precipitation in the recent past. CRHyME's validation has been assessed through NSE (Nash–Sutcliffe efficiency) and RMSE (root mean square error) hydrological-error metrics, while for landslides the ROC (receiver operating characteristic) methodology was applied. CRHyME has been able to reconstruct the river discharge at the reference hydrometric stations located at the outlets of the basins to estimate the sediment yield at some hydropower reservoirs chosen as a reference and to individuate the location and the triggering conditions of shallow landslides and debris flows. The good performance of CRHyME was reached, assuring the stability of the code and a rather fast computation and maintaining the numerical conservativity of water and sediment balances. CRHyME has shown itself to be a suitable tool for the quantification of the geo-hydrological process and thus useful for civil-protection multi-hazard assessment.

SLEM (Shallow Landslide Express Model): A Simplified Geo-Hydrological Model for Powerlines Geo-Hazard Assessment

“…For those types, the local geological component has a second-order effect with respect to the topography (slopes), and the geotechnical characteristics of the soil layers (angle of friction and cohesion) are responsible for their movement [12,42,44]. According to the literature [12,42,44,45,52,79], the most common approach to assess terrain stability follows the limit equilibrium equation applied on the infinite slope (Figure 3a). Here, each piece of terrain is subjected to mobilizing (M, in [N]) and resisting (R, in [N]) forces, which are derived by [50,70] for a cohesionless condition as reported in Equation (11).…”

“…By imposing the critical condition FS = 1 for the landslide ignitions, it is possible to determine explicitly the critical soil water height hw that can trigger the failure. The ratio Following the work of [71], Equation ( 11) is reworked, adding two terms that are generally required for assessing slope stability for natural slopes: the cohesion and the vegetation surcharge [52,71] (Figure 3b). The cohesion represents the additional resistance given by the soil and tree roots and is a significant contribution to terrain stability, especially over steep slopes.…”

“…The cohesion represents the additional resistance given by the soil and tree roots and is a significant contribution to terrain stability, especially over steep slopes. Soil cohesion 𝐶 𝑠 is generally comprised between 0-20 kPa [52], which could be neglected for coarse and sandy soils, while it tends to increase for clay soils. Tree root cohesion 𝐶 𝑟 is related to the presence of forest above the slopes and is generally comprised between 0-10 kPa [52].…”

“…Soil cohesion 𝐶 𝑠 is generally comprised between 0-20 kPa [52], which could be neglected for coarse and sandy soils, while it tends to increase for clay soils. Tree root cohesion 𝐶 𝑟 is related to the presence of forest above the slopes and is generally comprised between 0-10 kPa [52]. The presence of vegetation can also contribute to the stability through the surcharge W, which is consistent in a dense and mature forest up to values of 2-5 kPa [52].…”

“…This model has been implemented, revised and extended by other authors [48][49][50] trying to overcome its limitations regarding the steady-state hydrological model and including a more complete slope stability routine. However, these solutions have not always considered the influence of the terrain's partial saturation conditions on slope stability which is a determinant for accurate failure prediction [51,52].…”