Erick Carlier

Using ArcGIS® Modelbuilder and Aerial Photographs to Measure Coastline Retreat and Advance: North of France

Abstract Chaaban, F.; Darwishe, H.; Battiau-Queney, Y.; Louche, B.; Masson, E.; El Khattabi, J., and Carlier, E., 2012. Using ArcGIS® Modelbuilder and aerial photographs to measure coastline retreat and advance: North of France. Coastal areas are naturally dynamic with changes occurring over periods of time. When the shoreline moves landward, coastal erosion becomes a serious problem, and the rate of change has to be calculated. Coastline retreat is one of the best indicators of coastal erosion. Here, the geographic information systems (GIS) platform (ArcGIS® 9.3.1; Esri software) is used to study the long-term (last 59 years) shoreline change in the area of Hardelot-Plage and Sainte Cécile–Plage (a north–south 14-km-long beach), in northern France. The primary aim of this study was to develop a methodology for calculating shoreline change using ArcGIS Modelbuilder and aerial photographs. Changes in 14 coastlines over the course of 59 years (from 1946 to 2005) were digitized and represented in ArcGIS 9.3.1 platform. Two hundred and ninety-two transects perpendicular to the shoreline were used to estimate coastal erosion and deduce the recession rate. The Modelbuilders (two models) created and used in this work are generic models that can be used for geoprocessing linear features. One model can be used to ascertain the intersection between linear features (transects and shorelines), adding a new field to the attribute table and calculating the geometry of the intersection points. A second model can be used to add a new field to the attribute table and calculate the distance on the transect lines between the linear reference feature and other linear features, in this study between the baseline (established adjacent to the series of shoreline positions) and the shoreline. The results show that the shoreline change rates between 1947 and 2005 along the Hardelot and Sainte Cécile coasts are generally negative; 82.2% of transects have values less than zero (i.e., retreat) and outside of the error margin (±10 m). Nevertheless the shoreline change shows successive phases of advance and retreat over the same period.

Geographical information system approach for environmental management in coastal area (Hardelot-Plage, France)

The use of geographic information system (GIS) minimizes the effort and improves the efficiency of numerical models. The GIS provides a platform for high capacity collection, management, manipulation, analysis, modeling and display of spatial data. The conceptual model is created using GIS objects including points, arcs and polygons so that it can accurately represent real world condition. According to the research problem, the geographical model is based on Hypergraph Based Data Structure method, and a conceptual data model has been created from which a physical data model was elaborated in ArcGIS9.3 platform. The groundwater modeling system (GMS) provides a powerful tool for hydrodynamics modeling and it is able to solve complex problems such as the groundwater flow and seawater intrusion. The sand-dune system of Hardelot-Plage (North of France) suffers from a lack of well-developed foredune. This problem is linked to the almost constant saturation of beach sand which is the potential source of dune nourishment. In the south of Hardelot, the coastline is slowly, but constantly retreating. To remedy this situation, a coupling between a GIS and GMS was adopted, in order to find the possible scenarios which could lower the piezometric surface in the concerned area and allow dune nourishment again. The GMS used supports the Modflow-2000 code. A direct approach to designing Modflow finite difference model is tedious and less intuitive, specifically for complex boundary and initial conditions. Therefore, a Modflow model can be developed either using a grid or conceptual model approach. The preparation of input data modeling is tedious and takes a long time. The model created in GMS was calibrated against the historical and observed water level data for 1995–2006. Then a hydrodispersive model (MT3d code in GMS) was launched for evaluating sea-water intrusion. The model was run to generate groundwater and salt concentration scenario during pumping tests.

Tectonic and hydrodynamic control of landslides in the northern area of the Central Rif, Morocco

The northern edge of the Central Rif (Morocco) is subject to numerous landslides where mechanisms do not correspond to the classical models used by geomechanics specialists. It is necessary to adopt a multidisciplinary approach that combines geomorphology, geology, hydrogeology, and geotechnics in order to understand how such slope failures are generated, especially in a region with a heterogeneous structure characterised by significant lithological differences, severe fracturing, and thrust sheets where tectonic contacts play a major role in groundwater circulation. This report shows that these failures are essentially controlled by the tectonic contact separating the Tisirene and Chouamat thrust sheets and by subsurface hydrodynamic conditions. A model of spatial and temporal variations in the factor of safety is proposed.

Proposal for a probabilistic model of dispersion: A first validation

The probabilistic approach is used to simulate the particle tracking for two types of porous media. The first one is sand grains with a single intergranular porosity. The particle tracking is carried out by advection and dispersion. The second one is chalk granulates with intergranular and matrix porosities. Sorption can occur with advection and dispersion during particle tracking. The particle tracking is simulated as the sum of elementary steps with independent random variables in the sand medium. An exponential distribution is obtained for each elementary step and shows that the whole process is Markovian. A gamma distribution or probability density function is then deduced. The relationship between dispersivity and the elementary step is given using the central limit theorem. The particle tracking in the chalky medium is a non-Markovian process. The probability density function depends of a power to the distance. Experimental simulation by dye tracer tests on a column have been performed for different distances and discharges. The probabilistic approach computations are in good agreement with the experimental data. The probabilistic computation seems an interesting and complementary approach to simulate transfer phenomena in porous media with respect to the traditional numerical methods.

The Effect of Rock Collapse on Coastal Cliff Retreat along the Chalk Cliffs of Northern France

ABSTRACT El Khattabi, J.; Carlier, E., and Louche, B., 2018. The effect of rock collapse on coastal cliff retreat along the chalk cliffs of northern France. Coastal retreat is a topic that concerns all countries located on the coastal edge. This is the case for the chalky cliffs located in the north of France. Here, the cliff base is characterized by chalk rock rich in clay with low mechanical characteristics. To understand the appearance of rock collapses causing cliff retreat, the methodology applied in this report is based on an analytical study and numerical modeling. The model developed with CESAR (i.e. finite element software dedicated to stability) shows deformation affecting gray and blue chalk with separations reaching 3 cm. Simulations carried out with UDEC (i.e. Universal Distinct Element Code) show that constraints are organized around joints when the blocks rearrange themselves, and the effects are mainly seen at the base of the cliff. This study demonstrates the appearance of irregular conjugate fractures within the marly levels of the blue chalk. This type of fracture appears as a result of pressure from the overlying layers and the influence of lateral stress induced by the “Grand Blanc Nez” formation. These fractures propagate towards the gray chalk and set the limits of different blocks. The displacement of these blocks leads to the obstruction of conduits, which increases the water pressure. The destabilization of the cliff is reflected in the appearance of release cracks, which are strongly influenced by variations in groundwater level. These findings were verified by numerical modeling. This example demonstrates that rock collapses are responsible for coastline retreat in this area. The combination of unpredictable natural phenomena associated with a concentrated spatial area creates a high-risk coastal area retreating at around 0.25 m/y.

Comment on “Tank-reservoir drainage as a simulation of the recession limb of karst spring hydrographs”: paper published in Hydrogeology Journal (2011) 19:1009–1019, by Francesco Fiorillo

The subject article (Fiorillo 2011) gives an analytical solution from an analog model to simulate the recession limb of a spring hydrograph. The model is based on the drainage of three cylindrical tank-reservoirs in series with different bases. The process has been simulated using Bernouilli’s law by considering: a Torricelli reservoir, characterized by a linear decrease of discharge; and Darcy’s law and Poiseuille’s law, where discharges are assumed to decrease exponentially with time, giving a straight line in a semi-logarithm plot. The study of this paper may lead readers to consider that an exponential decrease would be only related to a porous cylindrical reservoir or a cylindrical reservoir with a small outlet orifice where friction forces and water viscosity take effect. In fact, an exponential decrease of discharge can also occur in a condition of free-flow discharge, where no energy is lost during the process. Consider a reservoir whose walls are curved as illustrated in Fig. 1: Equation 5 in Fiorillo (2011) is: