The horizontal component of land subsidence is typically assumed to be negligible, although recently, theoretical simulations have shown that horizontal strain is significant. A field based investigation in Mesquite, NV, was undertaken from May to July, 2003, for the purpose of evaluating the significance of horizontal strain during an aquifer test. The hydraulic heads in the aquifer were monitored within a meter of the municipal pumping well used for the aquifer test and also at a distance of approximately 1,470 meters from the pumping well. Aquifer deformation in the horizontal and vertical directions were measured using GPS for the first 22 days of pumping in 10 different locations at radial distances from the well varying from 100 meters to 2500 meters. From 22 to 60 days of the aquifer test, the number of GPS stations monitoring deformation was reduced to five. Radial displacement was measured at all monitoring stations during the aquifer test, indicating that the aquifer is moving closer to the pumping well. The greatest magnitude displacement measured 140 m from the well was approximately 10 mm at the land surface. A zone of radial compression occurred between the pumping well and the first monitoring station 140 m away from the pumping well. Vertical displacement was measured in decreasing magnitude with increasing distance from the well. Because GPS is not as precise a tool in the vertical direction as it is in the horizontal, the vertical signal of displacement is not as accurate. Numerical simulations using the BIOT and IBS codes were performed to reproduce the aquifer test and land deformation. The model included six layers representing three hydrogeologic units: a bottom aquifer (four layers) in which pumping occurred , a top aquifer (one layer) in which the monitoring well was screened, and a semi-confining bed (one layer) between the two aquifers that represented an equivalent thickness of interbeds and clays layers. The Biot code was used to simulate radial and vertical movements in an axisymmetrical simulation, while the IBS code was used to simulate only vertical displacement but also provided for the simulation of elastic and inelastic storage and compression. The vertical distribution of radial displacement was simulated using the BIOT code. At the onset of pumping, the greatest radial displacement occurred in the bottom aquifer in which pumping occurred. At a distance of 2,000 m from the well, the radial displacement was uniform over all depths indicating that the differences in hydraulic diffusivity are not as important a factor at distance from the well. The change in porosity that occurred as a result of horizontal strain was greatest in the bottom aquifer. Using the strain calculated directly from the GPS measurements at the land surface, vertical strain comprised almost 99% of the volume strain at the land surface. However, when the strain was simulated over the entire aquifer system, the radial and hoop strain contributed more than vertical strain in the bottom aquifer at a radius of 100 m from the pumping well at the onset of pumping until the aquifer reached near equilibrium, at which time vertical strain again dominated. / Master of Science

The first part of this thesis aims at defining the conditions triggering muddy floods in the Belgian loess belt. On average, each municipality is confronted with 3.6 muddy floods each year. Annual costs associated with their off-site impacts are estimated at € 16-172 millions for the entire Belgian loess belt. A topographic threshold is derived to predict the source areas of muddy floods. Furthermore, the storms required to produce a flood are, on average, smaller in May and June (25 mm) than between July and September (46 mm). This difference is explained by the variability of soil surface characteristics that determine the runoff potential of cultivated soils (soil cover by crops and residues, soil surface crusting and roughness). Steady state infiltration rates of cropland and grassed areas were characterised in the field using a 0.5 m2-portable rainfall simulator. Overall, grassed areas have a lower infiltration rate (16-23 mm h-1) than croplands (25-52 mm h-1). Muddy floods are mostly observed between May-September because of the coincidence of critical soil surface conditions for runoff generation with the most erosive storms. After an adaptation of its decision rules to the local conditions, the STREAM expert-based model provides satisfactory runoff/erosion predictions at the catchment scale. The second part of the thesis aims at evaluating the effectiveness of measures to control muddy floods. A modelling case-study showed that peak discharge was reduced by more than 40% by installing a grassed waterway and a dam at the outlet of a 300 ha-catchment. Monitoring the same catchment (2002-2007) demonstrated that the grassed waterway as well as three dams prevented any muddy flood in the downstream village despite the occurrence of several extreme storms (with a maximum return period of 150 years). Peak discharge was reduced by 69%. Specific sediment yield dropped from 3.5 t ha-1 yr-1 to a mean of 0.5 t ha-1 yr-1 after the installation of the control measures, thereby reducing drastically sediment transfer to the alluvial plain. Finally, a methodology is provided to implement grassed waterways and earthen dams in other dry valleys in the Belgian loess belt and comparable environments.

The aim of this study was to develop and examine the use of backscatter data collected with multibeam sonar (MBS) systems for benthic habitat mapping. Backscatter data were collected from six sites around the Australian coastal zone using the Reson SeaBat 8125 MBS system operating at 455 kHz. Benthic habitats surveyed in this study included: seagrass meadows, rhodolith beds, coral reef, rock, gravel, sand, muddy sand, and mixtures of those habitats. Methods for processing MBS backscatter data were developed for the Coastal Water Habitat Mapping (CWHM) project by a team from the Centre for Marine Science and Technology (CMST). The CMST algorithm calculates the seafloor backscatter strength derived from the peak and integral (or average) intensity of backscattered signals for each beam. The seafloor backscatter strength estimated from the mean value of the integral backscatter intensity was shown in this study to provide an accurate measurement of the actual backscatter strength of the seafloor and its angular dependence. However, the seafloor backscatter strength derived from the peak intensity was found to be overestimated when the sonar insonification area is significantly smaller than the footprint of receive beams, which occurs primarily at oblique angles. The angular dependence of the mean backscatter strength showed distinct differences between hard rough substrates (such as rock and coral reef), seagrass, coarse sediments and fine sediments. The highest backscatter strength was observed not only for the hard and rough substrate, but also for marine vegetation, such as rhodolith and seagrass. The main difference in acoustic backscatter from the different habitats was the mean level, or angle-average backscatter strength. However, additional information can also be obtained from the slope of the angular dependence of backscatter strength. / It was shown that the distribution of the backscatter. The shape parameter was shown to relate to the ratio of the insonification area (which can be interpreted as an elementary scattering cell) to the footprint size rather than to the angular dependence of backscatter strength. When this ratio is less than 5, the gamma shape parameter is very similar for different habitats and is nearly linearly proportional to the ratio. Above a ratio of 5, the gamma shape parameter is not significantly dependent on the ratio and there is a noticeable difference in this parameter between different seafloor types. A new approach to producing images of backscatter properties, introduced and referred to as the angle cube method, was developed. The angle cube method uses spatial interpolation to construct a three-dimensional array of backscatter data that is a function of X-Y coordinates and the incidence angle. This allows the spatial visualisation of backscatter properties to be free from artefacts of the angular dependence and provides satisfactory estimates of the backscatter characteristics. / Using the angle-average backscatter strength and slope of the angular dependence, derived by the angle cube method, in addition to seafloor terrain parameters, habitat probability and classification maps were produced to show distributions of sand, marine vegetation (e.g. seagrass and rhodolith) and hard substrate (e.g. coral and bedrock) for five different survey areas. Ultimately, this study demonstrated that the combination of high-resolution bathymetry and backscatter strength data, as collected by MBS, is an efficient and cost-effective tool for benthic habitat mapping in costal zones.

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós–Graduação em Oceanografia Biológica, Instituto de Oceanografia, 2006. / Submitted by Cristiane Gomides (cristiane_gomides@hotmail.com) on 2013-12-16T02:44:18Z No. of bitstreams: 1 PedrodeSa.pdf: 1303104 bytes, checksum: 596561a98d86d6219a45778a049ce092 (MD5) / Approved for entry into archive by Sabrina Andrade (sabrinabeatriz@ibest.com.br) on 2013-12-18T18:16:36Z (GMT) No. of bitstreams: 1 PedrodeSa.pdf: 1303104 bytes, checksum: 596561a98d86d6219a45778a049ce092 (MD5) / Made available in DSpace on 2013-12-18T18:16:36Z (GMT). No. of bitstreams: 1 PedrodeSa.pdf: 1303104 bytes, checksum: 596561a98d86d6219a45778a049ce092 (MD5) Previous issue date: 2006 / Este trabalho objetiva avaliar a estrutura e dinâmica da associação de macroinvertebrados bentônicos da zona entremarés de dois locais com distintas características ambientais da praia do Cassino, RS, Brasil. O local 1 possui características de praia dissipativa extrema, sedimentos finos e baixa hidrodinâmica, enquanto que o local 2 características dissipativas/intermediárias, sedimento mais grosseiros e maior hidrodinâmica. Eventos esporádicos de deposição de lama são observados no local 1. Foi realizado um acompanhamento durante 14 meses (abril/04 até maio/05) com amostragens mensais. Os 2 primeiros meses foram considerados como piloto, sendo seus dados abordados no capítulo III. Em cada local, foram demarcadas três transversais (separadas por 50m) perpendicular a linha d’água, nas quais amostras foram coletadas em triplicata em 4 níveis (separados por 10 m). As transversais se estenderam desde 10m acima do varrido superior, até cerca de 1m de profundidade. No capítulo I, foi considerada a variabilidade temporal da associação. Esta apresentou uma marcada dinâmica, sendo as principais variações ligadas às dinâmicas populacionais e perturbações físicas. Durante o inverno foram observadas baixas densidades, as quais foram relacionadas à ausência de recrutamentos, deposição de lama em abril e embancamentos de baixas intensidades. Na primavera ocorreu explosão populacional de Scolelepis gaucha, migração de adultos de Mesodesma mactroides do infralitoral para a zona entremarés e um evento de embancamento. Durante o verão foram observados recrutamentos de M. mactroides, Donax hanleyanus e Emerita brasiliensis. O outono foi caracterizado por baixas densidades, exceto pelo recrutamento de D. hanleyanus. O capítulo II abordou a distribuição perpendicular à linha d’água e paralela à linha d’água da fauna em diferentes escalas. O local 2 apresentou maior diversidade do que o local 1. A diversidade foi maior provavelmente devido a presença dos anfípodes Phoxocephalopsis sp. e Plastyschnopidae, os quais estiveram praticamente ausentes no local 1. Verificou-se que praias dissipativas/intermediárias podem suportar maior diversidade da macrofauna bentônica do que as dissipativas extremas, possivelmente, pela capacidade da associação macrozoobentônica de se beneficiar da maior hidrodinâmica na zona de varrido. As diversidades menores no local 1, podem ainda, ser atribuídas as perturbações causadas pelas deposições esporádicas de lama. Através de análises multivariadas foram identificadas 3 zonas: o mesolitoral médio, o superior do varrido e o inferior do varrido juntamente com a arrebentação interna. As espécies características de cada zona variaram com a estação do ano. Foram observadas densidades decrescentes do mesolitoral em direção ao infralitoral. Não foram evidentes padrões de distribuição paralela à linha d’água na escala de dezenas de metros, devido a grande homogeneidade sedimentar registrada nesta escala. No capítulo III foram analisados com maiores detalhes dois eventos: mortalidade pós deposição de lama em abril/04 e embancamento em outubro/05. A recomposição da fauna mostrou-se bastante rápida, em ambos eventos, registrou-se a mesma composição após 3 meses, entretanto as populações foram caracterizadas por organismos juvenis e recém assentados. Sendo que a manutenção de estoques adultos foi afetada. A deposição de lama ocasionou a mortalidade de toda a associação. O evento de embancamento afetou, principalmente, os juvenis+adultos do bivalvo M. mactroides. É provável que esses eventos sejam o principal fator estruturador de longo prazo das associações destes locais. / The present study aims to analyze the structure and dynamics of the intertidal macrobenthic assemblages in two sites with distinct environmental characteristics of Cassino beach, RS, Brazil. Site 1 can be characterized as an extreme dissipative beach, with fine sediments and low hydrodynamics and site 2 is a dissipative/intermediate beach, with coarser sands and high hydrodynamics. Sporadic muddy deposition events occur in site 1. Sampling was conduct monthly from april/2004 to may/2005. Data from the fist two months was considered as a pilot study and was included just in chapter III. In each site, three transect lines, spaced 50 m apart, were defined perpendicular to the shore line, samples were collect in triplicate in 4 levels (10 m apart). Each transect was extend from 10 above de swash limit to 1m deep in the inner surf zone. Chapter I aimed to describe the temporal variability of the intertidal assemblages. A striking dynamics was recognized through samplings times. The mains temporal changes were influenced by the population dynamics of numerically dominants species and physical disturbances. In winter was found a low density and diversity of the assemblages, with were related to absence of recruitments, an event of muddy deposition and stranding events of low effects. In spring was observed a population explosion of the polychaeta Scolelepis gaucha, migration of Mesodesma mactroides adults from the subtidal to the intertidal and a strand event. During summer was observed recruitments of tidal migrant species as M. mactoides, Donax hanleyanus and Emerita brasiliensis. Fall was characterized by low densities, except for an expressive recruitment of D. hanleyanus. Chapter 2 aimed to describe the spatial distribution across shore and along shore in distinct scales. Site 2 showed a higher diversity than site 1. The higher diversity were probably due the presence of amphipods Phoxocephalopsis sp. and Plastyschnopidae in site 2, which were absent in site 1. The results showed that dissipative/intermediate can support higher diversities than extreme dissipative conditions, probably because the assemblage can be beneficiated by the higher hydrodynamics of swash. The low diversities found in site 1, may be also related to sporadic muddy deposition events. The multivariate analyses showed three macrofaunal zones: mesolitoral; the higher swash; the lower swash together with the inner surf zone. The characteristics species of each zone varied according to the season. A decrease of density was verified from mesolitoral zone to the lower levels. No patterns were identified in a smaller scale (50m) of the along shore distribution, probably due the high homogeneity of the morpho-dynamics and sediments in this scale. In Chapter III, the period that occurred two mortality events were analyzed with more detail: muddy deposition in april/2004 and stranding in october/2004. The recuperation of the macrofauna assemblages was extremely fast, in three months they showed the same composition, although the populations were characterized by high densities of recruitments and juvenis. The adult stokes may be heavily impacted by this events. The muddy deposition caused a mortality of all population of the intertidal assemblages. The bivalve M. mactroides juvenis+adults was the organism most affected by the strand event. It’s likely that these events are the main long term factors structuring this assemblage.