From their beginnings some 4,000 years ago to their decadence around 400 b.c., the Olmec people achieved a high level of sociopolitical complexity and dominated their native geographic territory, the southern Gulf Coast of Mexico. The first Olmec capital of San Lorenzo, Veracruz, was the only site in Mesoamerica that produced imposing monumental stone sculpture and architecture between 1800 and 1000 b.c. These characteristics reflect the capabilities of its centralized political system headed by hereditary rulers with divine legitimation. Key issues regarding the development of San Lorenzo Olmec culture center on subsistence and environment. The present study focuses on a portion of the landscape located immediately north of the first Olmec capital of San Lorenzo, Veracruz, that has been proposed as a key resource area during the development of the first civilization in Mesoamerica. We calculate the surface, volume, and water depth of this area based on archaeological data and a Digital Terrain Model (DTM) derived from an airborne Light Detection and Ranging (LiDAR) survey. The expected minimum and maximum area, local minimum altitude, and the DTM of 5-m spatial resolution provide a basis for inferences regarding the characteristics of the wetland ecosystem during Olmec times. The goal is to quantify and qualify the potential of this resource zone relying on LiDAR topography. Our models validate the observations in the field and, when combined with algorithms, they confirm the archaeological conclusions. We affirm that the northern plain in Olmec times was deeper than it is today and would have been a source of abundant aquatic resources for the primary subsistence of the early Olmec society.

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Abstract. The irregularities of the earth’s surface are quantified by means of roughness measurements using Digital Elevation Models (DEM’s). This article presents a roughness measurement method that is based on the calculation of the difference of altitude existing between a plane passing through the centre of a moving window and the altitude of the DEM surface inside this window. This method differs from the measure of the standard deviation and best fit plane, in the sense that it considers all difference values, positives or negatives. The measurement is done in a 3 × 3 or a 5 × 5 moving window and contemplates inside this window the plane which passes through the centre of the window and the highest pixel located in the border or perimeter of this window. According to the 3D configuration of the DEM surface inside the moving window, the sum of all the differences is positive or negative, allowing to discriminate the local morphology independently of the global roughness. The roughness variable which distinguishes negative and positive values allows to classify accurately landscape units such as watersheds, riverbeds, volcanic assemblages as well as landforms associated with tectonic structures.

In the flood simulation method presented here, different approaches reconstitute at a regional scale flooded areas according to the displaced volume. The developed algorithm creates a flood surface whose slope is calculated according to field observations. The surface thus obtained is superposed on a DEM in order to define the extension of the submerged areas. A concave surface of the flood would correspond to the flux entering in the study region; a convex surface would represent the accumulation or the final stage downstream. On the other hand, slight Gaussian functions are used to simulate local water accumulations and flooding waves related to the sliding motion of the water surface.Such simulations can be used to monitor the areas of potential flood affecting flat coastal plains.

ABSTRACT:This research provides a wave flood simulation using a high resolution LiDAR Digital Terrain Model. The simulation is based on the generation of waves of different amplitudes that modify the river level in such a way that water invades the adjacent areas. The proposed algorithm firstly reconstitutes the original river surface of the studied river section and then defines the percentage of water loss when the wave floods move downstream. This procedure was applied to a gently slope area in the lower basin of Coatzacoalcos river, Veracruz (Mexico) defining the successive areas where lateral flooding occurs on its downstream movement.