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Floods cause severe natural disasters over the world generating property and infrastructures damages, poverty and loss of human life, among others. Mediterranean watersheds are especially sensible to floods due to their typical drainage basin features (steep slopes, short concentration times, complex orography, etc.) and the high rainfall intensity typical of convective systems. Knowing channel dimensions and other fluvial morphological features is key to (i) understanding the morphological evolution of the fluvial system in response to changes in land use and climate, and (ii) as an input for hydrological and erosion modelling. The objective of this study is to develop a simple method to obtain reliable estimates of channel dimensions and granulometry of bed material, based on statistical relations with catchment characteristics (e.g. topography, land use, soil properties, lithology, precipitation, connectivity indicators).First, channel dimensions were estimated based on GIS analysis using a high resolution digital elevation model (2x2m) and ortophotos (50 cm resolution) for the Upper Segura River catchment, a Mediterranean catchment of 2,592 km2 located in the southeast of Spain. These estimates were validated with field measurements of depth and width of bankfull channels in the catchment headwaters. This comparison revealed that there was generally good agreement between channel dimensions obtained with the GIS method and those observed in the field for all evaluated channels (depth: RMSE=0.06; R2=0.93; width: RMSE=0.59, R2=0.45), although with better results for dry channels than for channels with continuous water flow. At each field observation, we also took sediment samples and characterised the granulometry of the channel bed material in the laboratory through dry sieving. Preliminary results show that bed material is composed mainly by gravels (67.8%), followed by sands (31.1%) and clays and silts (1.1%). Next, channel dimensions, obtained using GIS analysis across the entire catchment, and granulometry of bed material were used as dependent variables in advanced statistical analyses (such as machine learning algorithms) at sub-basin scale, with catchment characteristics as independent variables. The outcome of this analysis is now being used to make spatially continuous predictions of channel dimensions and granulometry of bed material at the catchment scale. This information will then ultimately serve as input for a coupled model that simulates channel hydraulics and morphodynamics at the catchment level.Keywords: geomorphology; sediment yield; depth and width of bankfull channels; Mediterranean environment; GIS based tools; southeast of Spain.We acknowledge funding from the Spanish Ministry of Science and Innovation and ‘Agencia Estatal de Investigación’ (PID2019-109381RB-I00/AEI/10.13039/501100011033).

Soil erosion is one of the most important processes of soil degradation, especially vulnerable are many agricultural systems of SE Spain which are being transformed from a rainfed to irrigated agriculture. Crop diversification has been raised as a possible management measure with multiple benefits to combat soil degradation. Interrill soil erosion rates and processes were assessed in three land uses in SE Spain next to each other, with the same basic characteristics (climate, lithology and soils) representing a gradient of land use change: natural shrubland, rainfed almond crop (Prunus dulcis) on terraces and levelled citrus crops (Citrus reticulata) with street-ridge morphology. The experimental design included two diversifications in the rainfed almond: intercropping Capparis spinosa and Thymus hyemalis, respectively, while in the citrus irrigated area a rotation with Hordeum vulgare and Vicia sativa (from February to July) or Vicia faba (from October to January) were intercropped in the streets. In the rainfed and natural area interill erosion was measured using erosion pins with a 2 or 3 x 3 x 3 scheme (2 or 3 plots of 1 m2 with 9 pins at two diversifications and control, at three different agricultural terraces). In the natural area two pin plots were set up. At the irrigated area the experimental design was a 2 x 2 x 2 scheme (2 plots (ridge; street) x 2 replicates x 2 (bare, vegetated). Pins were measured after each rain event or each month during 14 months, identifying detachment (positive values) and sedimentation (negative values) within the erosion process. The preliminary results indicate significant higher erosion rates in the irrigated areas than in the traditional rainfed terraces (83.6±147.4 t ha-1 versus 9.59±170.34 t ha-1, respectively). Shrubland natural areas show significant higher deposition rates (-74.97±43.08 t ha-1) than recent diversified plots with Capparis and Thymus (-52.56±227.06 and -28.29±85.94 t ha-1, respectively). Neither differences within diversification type (Capparis versus Thymus) nor between control and diversifications in the rainfed almond area have been yet detected. In the Citrus irrigated area erosion rates under Hordeum vulgare and Vicia sativa were significantly higher than under Vicia faba (129.58±94.43 and 25.61±87.79 t ha-1, respectively).So far, those preliminary results indicate that natural shrubland and traditional rainfed crop systems facilitate sedimentation rates and are effective systems for soil conservation. However, the conversion from rainfed to irrigated crops mean a significant increase of erosion rates due to a system that does not facilitate retention of detached soils. Within this temporal framework, crop diversifications, both in rainfed and irrigated systems, have not yet significantly reduced erosion rates. A longer experimentation period is necessary to determine the effect of crop diversifications on soil erosion.