Joël Daroussin

Mapping erosion risk for cultivated soil in France

Abstract Surface runoff and soil erosion are major threats to sustainable agriculture and mapping regional erosion risk is increasingly needed by national and international environment agencies. Because erosion results from the interaction of several parameters which vary in space and time, no simple model can take into account all relevant factors, particularly in cultivated areas where human influences are predominant. The aim of this work is to develop a methodology based on present knowledge and available data for the evaluation of erosion risk at national scale. The various erosion factors have been graded for different geographical situations and erosion mechanisms have been expressed with the help of expert decision. The various erosion types observed in France had been previously classified. Soil crustability is considered as a key factor in runoff and erosion risk on cultivated soils. A geographical database has been created for French territory, and a model of erosion risk has been developed within a Geographical Information System (GIS). The model uses expert rules to combine data on land use (CORINE Land Cover database), soil crustability and soil erodibility (determined by pedotransfer rules from the French soil database), relief (Digital Elevation Model from the National Geographic Institute) and meteorological data from Meteo-France at the scale of 250×250 m pixels. Results are spatially aggregated using various administrative or environmental units. The main areas affected by erosion risk are the north, west and east of the Paris basin with intensive agriculture on crusting soils, the Rhone valley and southwest of France where vineyard or spring crops cover large areas. Other areas like Britany, the south of the Massif Central or the Mediterranean area are moderately affected. Areas with a permanent cover of woodland or grassland show a low erosion risk.

Crusting, runoff and sheet erosion on silty loamy soils at various scales and upscaling from m2 to small catchments

Water erosion is one of the most active processes in soil genesis and dynamics. It is also at the origin of significant environmental problems. Soil surface state is one of the most important factors for erosion risk assessment. However, it is not easy to determine the effect of this factor at a large scale. A field experiment was held in Pays de Caux (Normandy, France) in order to study and quantify crusting, runoff and sheet erosion at the cultivated field and catchment scales. We measured crust formation, runoff and erosion during two seasons on 1-m2, 20-m2 and 500-m2 experimental plots and on a small catchment. Results allow a ranking of the most important factors influencing crusting and erosion at the different scales. They also enable the development of relationships for upscaling from small plot results to the cultivated field and catchment for specific conditions. However, upscaling from plots to catchments is generally difficult and needs to take catchment spatial structures into account. We distinguish between runoff and erosion scale transfer, the latter being at the origin of specific problems that need further research to be solved.

Effects of tillage on runoff directions: consequences on runoff contributing area within agricultural catchments

Abstract In areas of intensive agriculture, e.g. ‘Pays de Caux’ in France, which was the study area, field observations have shown that runoff directions were modified by agricultural activities. In order to account for factors responsible for modifications of the runoff direction (roughness, tillage direction and agricultural patterns, e.g. dead furrow or dirt tracks), we constructed a discriminant function based on field observations. This function enables us to decide whether flow direction for slopes of up to 15% was imposed by slope direction or tillage direction. It can be applied to any location, provided there are known roughness, known slope intensity, known aspect and known tillage azimuth. In order to examine the effects of these agricultural activities at the catchment scale, we compared two models by analysing the same hydrological variables: the area contributing to runoff and the flow network. The first model (Topo) was built according to the runoff direction derived from a Digital Elevation Model (DEM). The second model (Tillage) was constructed by combining information from the DEM, and information from rules based on field observations or resulting from statistical analysis. For 23 basic catchments, the result of the comparison between the two models (Topo and Tillage) showed that a major part of the catchments and the drainage network was affected by modifications related to the introduction of man-made agricultural factors. For example, for 20 of 23 catchments, the runoff flows over more than 50% of the surface of such areas were produced along the direction imposed by tillage. The introduction of tillage effect brings about modifications of both the shape and size of catchments.

Development of a soil geographic database from the Soil Map of the European Communities

Abstract Questions on land use and soil conservation require increasingly accurate information on soil properties and their geographical location. Soil maps have helped to answer them thus helping in decision making. Information presented on soil maps are now managed by computer. This is the case for the Soil Map of European Communities (EC) at a scale of 1 : 1 000 000. Computerization of soil maps is often limited to soil boundaries and to the few descriptive items on the paper themselves. Much of the original survey is lost either during mapping or because it is published separately in explanatory notes or legends. This was also the case for the EC Soil Map. Many scientific publications and draft documents were used to make the original paper map, but were greatly condensed and simplified. The first version of the EC soil database is an exact copy of the paper map, thus having the same deficiencies. Using Geographical Information System technology, an efficient data structure has to be developed to take into account efficiently the internal organization of the soil cover. Such a structure should match conceptually the soil scientist review of spatial soil organization at a given scale within a computerized model. As a first step towards such a “Soil Spatial Organization Model” the material available for the compilation of the EC Soil Map is analysed. A logical data structure to receive a posteriori these informations is proposed and the databases improvement in terms of quantity as well as quality is demonstrated.

Soil Profile Analytical Database for Europe (SPADE): Reconstruction and Validation of the Measured Data (SPADE/M)

Abstract Geografisk Tidsskrift, Danish Journal of Geography 106(1):71–85, 2006 The Soil Profile Analytical Database of Europe of Measured profiles (SPADE/M) was created to provide a common structure for storing harmonized information on typical soil profile properties of European soils. The main difficulty encountered in constructing the database was the transfer of the source data from individual electronic spreadsheet pages to the more rigid structure of a relational database. The data in spreadsheet format had been collected more than 12 years earlier but pressure was mounting for the capability to link these data to the Soil Map of Europe. A semi-automatic process was implemented to transfer data from nominal positions on the spreadsheet page to an intermediate structure highlighting any deviations from expected values. Conflicting situations were solved by manual intervention and expert judgement. Data in the intermediate structure were subjected to a validation procedure with the aim of storing uniform data in the database. The validation checks cover format authentication, restricting entries to permissible values and those passing plausibility tests. In cases where a horizon property could not be represented consistently following the field specifications, the database structure was adapted to accommodate those conditions. The database model was extended to allow data from multiple samples taken at the same plot and from the analysis of samples from different laboratories to be stored.

Upscaling a simple erosion model from small areas to a large region

Upscaling from a catchment scale to a regional scale is generally rendered difficult by the lack of relevant and precise data at the larger scale. In this case, a winter rill erosion hazard map was produced for the Nord-Pas-de-Calais region using a linear regression erosion model originally designed for the catchment scale. Upscaling entailed adapting and applying the model at the county scale for all of the counties within the region. In upscaling the model, the difficulties associated with the nature of the data were dealt with in three stages: (1) the modification of the model for the county scale as a function of the nature of the data available, (2) an analysis of the influence of the spatial distribution of the data, (3) an analysis of the effect of the loss in precision of the data on the model output. Reference areas were used to verify the accuracy of the upscaling process before applying it to all of the counties in the region. In this case, the most significant limitation was the spatial coverage of the data: the basic administrative unit for which data is collected is the county, and it does not correspond to the erosion process scale which is the catchment. Defining erosion risk in terms of hazard categories rather than estimated erosion rates overcomes this difficulty to some extent. The use of reference areas provides several advantages in an upscaling procedure: these are mainly related to minimizing data collection and obtaining a reliable estimate of the accuracy of the predicted output.

Proposals for a spatial organization model in soil science (the example of the European Communities Soil Map)

Before computerized techniques were used, a paper soil map had to fulfill two functions: memorization or managing a maximum of data, and communication or transmitting a minimum of pertinent data on a given problem. Computer‐based techniques and, in particular Geographic Information Systems, enable the management, analysis, and easy organization and presentation of data about soils. An apparent first step would be to take older data in paper maps and convert them into a geographic database format using digitizing and other computer techniques. However, such work may be insufficient, as is demonstrated by analysis of the specific example of the European Communities Soil Map. Therefore, we propose a new relational structure for pedological or soil science information based upon the main conceptual concepts used during conventional cartographic work. This “Soil Spatial Organization Model,” or SSOM, is a computerized framework for coherent description of the geographical variability of soils, combined with other environmental criteria. It makes no prejudgment on the type of processing of such data. It stresses the importance of starting with the determination of the type of soil organization such as the identification of spatial units and their relationships to permit cartographic representations that show specific themes.

SRTM as a Possible Source of Elevation Information for Soil-landscape Modelling

“The Shuttle Radar Topography Mission (SRTM) obtained elevation data on a near-global scale to generate the most complete high-resolution digital topographic database of Earth’ [1]. Availability to the publiC., uniform cover of the Earth’s surface combined with a cell size acceptable for medium-scale soil modelling (90m on average) introduced the SRTM digital elevation model (DEM) as promising datasets for small and medium scale soil-landscape modelling and applications.

Calculation of Potential Drainage Density Index (PDD)

This paper focuses only on the technical details of the usage and creation of PDD. More details on the theory can be found in the papers written by (1998) and (2000). The Potential Drainage Density index, abbreviated as PDD, can be used for geomorphologic, pedologic and geologic characterisation of the landscape.

A Quantitative Procedure for Building Physiographic Units for the European SOTER Database

Soil data of various scales is needed for good management of agricultural and environmental resources. On the European level soil information is used for crop monitoring, yield forecasting, agricultural planning, feasibility studies for rural development, natural hazards forecasting, such as floods and landslides or slowly acting processes such as erosion, acidification and other types of chemical, biological and physical degradation of soils. However, no soil database for the European Union to support these goals had existed before the late eighties. The strong need for policy support has speeded up the database compilation and resulted in the first version of the Soil Geographical Database of Eurasia at scale 1:1 million (SGDBE1M). Despite its limitations, SGDBE1M is still among the few databases which serve as a flagship in the development of the small scale spatial databases in Europe. The version 2.0 of SGDBE1M was published recently, in 2004. The refinement of the database and the extension of its geographic coverage to Eurasia and the Mediterranean Africa are in preparation (ESB 2004)