El medio físico en la planificación y gestión del territorio. Algunos ejemplos

Physical environment has exerted a noteworthy influence on the location of human settlements. Modern cities have deeply changed their environment, often with negative a impact. The inclusion of the physical environment analysis into land-use planning can be justified by its restrictions on the urban growth, the necessity of minimizing the changes on the dynamics of natural systems, and the efficiency in the natural ressources management. According to their objectives, physical environment studies can be classified in land-use planning and environmental impact studies. The Besos river delta is shown as an example of conflictive physical environment management. Last decades pumping sites in the delta shifted and changed the groundwater levels. Basements built while levels were low, were drawn after the abandonment of the wells. To solve this problem, intensive pumping was decided in some cases to withdraw the water table. This solution along with new wells performed, induced the marine water to penetrate into the delta, forcing tlie abandonment of some water supply wells. Decission-makers hardly perceive the consequences of their decissions on the environment because of the natural processes time-scale. This is especially important in complex natural systems. In the Ebro river basin, headwater corrective works and water schemes are responsible for the present instability and regression at the delta front. We conclude that only a global management that takes into account the dynamics of natural systems would be able to give an answer to the problems created

Comparing rockfall scar volumes and kinematically detachable rock masses

Scenario-based risk assessment for rockfalls, requires assumptions for different scenarios of magnitude (volume). The magnitude of such instabilities is related to the properties of the jointed rock mass, with the characteristics of the existing unfavourably dipping joint sets playing a major role. The critical factors for the determination of the maximum credible rockfall volume in a study site, the Forat Negre in Andorra, are investigated. The results from two previous analyses for the rockfall size distribution at this site are discussed. The first analysis provides the observed size distribution of the rockfall scars, and it is an empirical evidence of past rockfalls. The second one, calculates the kinematically detachable rock masses, indicating hypothetical rockfalls that might occur in the future. The later gives a maximum rockfall volume, which is one order of magnitude higher, because the persistence of the basal planes is overestimated. The tension cracks and lateral planes interrupt systematically the basal planes, exerting a control over their persistence, and restricting the formation of extensive planes and large rockfall failures. Nonetheless, the formation of basal planes across more than one spacings of tension cracks is possible and small step-path failures have been observed too. Concluding, the key factor for the determination of the maximum credible volume at the study-site is the maximum realistic length of the basal planes, penetrating into the rock mass, their spacing, and, if applied, the contribution of the rock bridges to the overall rock mass resistance.Peer ReviewedPostprint (author's final draft

Evaluation of maximum rockfall dimensions based on probabilistic assessment of the penetration of the sliding planes into the slope

There is intrinsic difficulty in the investigation of the largest volume of rockfalls that is expected in an area, which lies in the small number of large events, in registrable times. The maximum credible rockfall size has been associated with the properties of the rock mass discontinuities, as they delimit detachable rock blocks, and in particular with the penetration of those discontinuities that comprise rockfall sliding planes. In highly fractured rock masses, the evaluation of the penetration remains an issue. A probabilistic methodology is proposed, to measure the penetration of potential sliding planes into the interior of a rocky slope. The main hypothesis of the method is that the sliding plane persistence is interrupted along its two directions, at the intersection with two lateral discontinuity sets, as the latter displaces the former. Due to the displacement, the sliding planes are formed by quasi-planes that contain a maximum number of spacings of the intersecting joints, hence their size is restricted. The methodology requires as an input the spacing of the intersecting joint sets. Its application to a granodiorite slope confirms that for the study site, there is a maximum volume of rockfalls, excluding the possibility of large stepped failures and rupture of rock bridges. The maximum calculated persistence for the two existing sliding planes in the study site is, respectively, 28.0 m and 48.5 m. The maximum calculated sliding plane surfaces are, accordingly, 282.5 m2 and 289.3 m2. These results are compared against the observed scar dimensions at the study site, which have been retrieved alternatively, by processing a LiDAR point cloud. The results from the two alternative sources are similar, indicating that the methodology can be efficiently used to assess the sliding plane persistence and the expected maximum rockfall magnitude at the study site.Peer ReviewedPostprint (published version

A fractal fragmentation model for rockfalls

The final publication is available at Springer via http://dx.doi.org/10.1007/s10346-016-0773-8The impact-induced rock mass fragmentation in a rockfall is analyzed by comparing the in situ block size distribution (IBSD) of the rock mass detached from the cliff face and the resultant rockfall block size distribution (RBSD) of the rockfall fragments on the slope. The analysis of several inventoried rockfall events suggests that the volumes of the rockfall fragments can be characterized by a power law distribution. We propose the application of a three-parameter rockfall fractal fragmentation model (RFFM) for the transformation of the IBSD into the RBSD. A discrete fracture network model is used to simulate the discontinuity pattern of the detached rock mass and to generate the IBSD. Each block of the IBSD of the detached rock mass is an initiator. A survival rate is included to express the proportion of the unbroken blocks after the impact on the ground surface. The model was calibrated using the volume distribution of a rockfall event in Vilanova de Banat in the Cadí Sierra, Eastern Pyrenees, Spain. The RBSD was obtained directly in the field, by measuring the rock block fragments deposited on the slope. The IBSD and the RBSD were fitted by exponential and power law functions, respectively. The results show that the proposed fractal model can successfully generate the RBSD from the IBSD and indicate the model parameter values for the case study.Peer ReviewedPostprint (author's final draft

Some Formal Considerations on the Generation of Hierarchically Structured Expressions

In this note we define a machine that generates nests. The basic relations commonly attributed to linguistic expressions in configurational syntactic models as well as the device of chains postulated in current transformational grammar to represent distance relations can be naturally derived from the assumption that the combinatorial syntactic procedure is a nesting machine. Accordingly, the core of the transformational generative syntactic theory of language can be solidly constructed on the basis of nests, in the same terms as the general theory of order, an important methodological step that provides a rigorization of Chomsky's minimalist intuition that the simplest way to generate hierarchically organized linguistic expressions is by postulating a combinatorial operation called Merge, which can be internal or external. Importantly, there is reason to think that nests are a useful representative tool in other domains besides language where either some recursive algorithm or evolutionary process is at work, which suggests the unifying force of the mathematical abstraction this note is based on

Postglacial deformation history of sackungen on the northern slope of Pic d'Encampadana, Andorra

Slopes undergoing deep-seated gravitational deformation create surface landforms that, if trenched and dated, yield critical data on slope kinematics. The northern slope of Pic d'Encampadana descends steeply 800 m down into the glaciated Valira d'Orient of Andorra and has long been known for its numerous antislope scarps (sackungen), indicative of deep-seated gravitational slope deformation (DSGSD). We excavated three trenches across antislope scarps and their adjacent troughs to date the deformation structures and to infer slope kinematics. Trough deposits have been disrupted by normal and reverse faulting, with the largest fault zone underlying the antislope scarp and dipping into the slope at 40°-80°. Trenches in the troughs expose fining-upward sequences of strata from which we interpret several cycles of: (1) episodic downdropping along graben faults and deepening of the topographic trough, (2) filling the trough with marginal colluvial and axial sag-pond sediments, followed by (3) a hiatus of soil profile development. The average time between deformation events in any one trench in the past 12–15 ka is about 3–3.5 ka. Deformation seems to have begun first in the lower part of the northern slope (1935 m elevation) about 15.3 ka, and had spread to the upper parts of the slope (2320 m) by 11.6 ka. Deformation in the lower slope ceased after 5.5 ka, but continued higher on the slope into the mid-late Holocene. The youngest deformation dated (1.4–1.6 ka) occurred in the highest trench on the slope. This pattern of younger deformation with increasing elevation has been documented at several other sites and has been ascribed to an upslope-migrating extensional stress field which originated at the base of the slope from glacial oversteepening and end-glacial debuttressing.Peer ReviewedPostprint (author's final draft