Matthew Wilson

Modeling large‐scale inundation of Amazonian seasonally flooded wetlands

This paper presents the first application and validation of a 2D hydrodynamic model of the Amazon at a large spatial scale. The simulation results suggest that a significantly higher proportion of total flow is routed through the floodplain than previously thought. We use the hydrodynamic model LISFLOOD-FP with topographic data from the Shuttle Radar Topography Mission to predict floodplain inundation for a 240 × 125 km section of the central Amazon floodplain in Brazil and compare our results to satellite-derived estimates of inundation extent, existing gauged data and satellite altimetry. We find that model accuracy is good at high water (72% spatial fit; 0.99 m root mean square error in water stage heights), while accuracy drops at low water (23%; 3.17 m) due to incomplete drainage of the floodplain resulting from errors in topographic data and omission of floodplain hydrologic processes from this initial model.

The use of elevation data in flood inundation modelling: A comparison of ERS interferometric SAR and combined contour and differential GPS data

Abstract Three internationally‐available elevation models were assessed for suitability for use in the prediction of flood inundation. The elevation data were selected because they represent data which may be available in data‐poor developing countries. These were a contour data set, a remotely sensed dataset (interferometric SAR) and a dataset which may be obtained rapidly through a differential global positioning system (DGPS) survey. The latter dataset was known to have much less uncertainty than the contour dataset and was, therefore, accepted as a benchmark against which to test the other two. Each dataset was used to predict flood inundation for an event in the United Kingdom in 1998 using the two‐dimensional model LISFLOOD‐FP. The contour dataset was different in spatial character (overly smooth) to the DGPS dataset and resulted in substantial differences in the timing and extent of flood inundation. The interferometric SAR dataset was also different in spatial character (overly rough) to the DGPS dataset although the differences in the timing and extent of flooding were not as great as for the contour dataset. However, results demonstrate potential problems with the use of satellite remotely sensed topographic data in flood hazard assessment over small areas.

Sensitivity of a flood inundation model to spatially-distributed friction

In this paper, land cover was predicted from Landsat TM imagery and used to generate spatially-distributed friction coefficients. Flood inundation was then predicted using the raster-based model LISFLOOD-FP, based on friction and three different elevation models. Sensitivity of LISFLOOD-FP to spatially-distributed friction was assessed. It was found that effect of friction on the flood wave is small when compared to the underlying elevation, but is greatest during the recession phase of the hydrograph. Hydraulic models of channel and overland flow allow river discharge to be related to flood inundation extent, by simu- lating flooding based on a scenario discharge. An important boundary condition for such models is surface friction. In particular, floodplain land cover is related to friction that affects the movement of the flood wave. However, the selection of appropriate friction coefficients for hydraulic models is difficult and it is recognised that floodplain friction coefficients have considerable uncertainty and sensitivity associated with them (1). Specific problems are (i) a lack of data sources, (ii) the often coarse spatial resolution of data and (iii) the use of stationary models (e.g., use of average friction over the whole catchment). Remote sensing can provide spatially distributed estimates of land cover, allowing a more informative and accurate representation of floodplain friction in flood inundation mod- els. However, hard classification may not provide sufficiently detailed land cover data at the sub-pixel scale. For example, where Landsat Thematic Mapper (TM) (spatial resolution of 30 m) imagery is used and the flood is only several hundred metres across, hard classification may be inappropriate. There- fore, in this paper, soft classification was used to estimate friction coefficients on a continuous scale for each cell on the floodplain. The objective was then to assess the sensitivity of a flood inundation model to uncertainty in these coefficients.

Sustainable management of tropical small island ecosystems for the optimization of soil natural capital and ecosystem services: a case of a Caribbean soil ecosystem—Aripo savannas Trinidad

PurposeThe unsustainable use of soil natural capital and ecosystem services is of global concern due to damage and losses on a worldwide scale. This situation is further compounded in small island developing states (SIDS), such as the Caribbean, where rapid population growth coupled with limited land space accelerates the rate of degradation of soil natural capital. The Aripo savanna is the largest surviving natural savanna in Trinidad with economic and scientific importance. Presently, there are many different land uses and land covers competing for space to the detriment of soil ecosystem services in this savanna. An ecosystem framework approach is needed to guide the development of adaptation strategies to improve the resilience of soil ecosystem for the provisioning of services, especially in the face of climate change.Materials and methodsWe reviewed the existing literature on soil ecosystem management in SIDS with particular emphasis on Aripo savanna and attempted to provide a better understanding of soil processes by developing frameworks for assessing tropical small island soil ecosystem services and soil health.Results and discussionIn tropical island states, poor soil quality has been associated with indiscriminant land use, creating short-term economic viability. Short-term economic viability is characterized by poor practices, negatively impacting on soil and thus limiting its ability to perform ecosystem services. To improve the resilience of a society, an ecosystem-framework approach becomes necessary. Soil ecosystem health, however, cannot be represented solely by specific land use(s)/land cover(s) (LULC) but by critical descriptors that influence soil quality.ConclusionsThis review highlights the importance of an ecosystem framework approach for the sustainable management and optimization of soil natural capital and ecosystem services in the Caribbean SIDS.

Cusp morphodynamics in a micro-tidal exposed beach

Beach cusps have attracted the focus of several studies due to their effect on sediment transport and their rhythmic presence in the midst of complex nearshore interactions among waves, currents and sediment. In this paper, cusp evolution is investigated to determine the factors which influence them within Maracas Bay, Trinidad, in the micro-tidal environment of the southern Caribbean. Data on beach profiles, beach sediment, coastal processes, and cusp dimensions were collected using standard geomorphological techniques across daily, weekly and seasonal time-scales. Results indicate that beach cusp dimensions are predominantly determined by beach volume and beach angle. These two parameters in turn are influenced by wave energy. In both the wet and dry seasons, periods of lower wave energy promote accretion, leading to the formation of smaller beach cusps; conversely, periods of higher wave energy and the associated increase in erosion result in the formation of larger beach cusps. There was agreement with the self-organization theory since cusps were always present along the beach, constantly changing morphologically but never completely being erased and recreated anew. Beach cusps form an integral part of the total sediment deposited and retained on beaches over tidal and seasonal cycles, with implications for nearshore currents and beach safety. As such, a proper understanding of their dynamics will help support planning and management of beaches as they go through cyclic phases annually.