An application of the distributed hydrologic model CASC2D to a tropical montane watershed

Increased stormflow in the Quebrada Estero watershed (2.5 km²), in the northwestern Central Valley tectonic depression of Costa Rica, reportedly has caused flooding of the city of San Ramón in recent decades. Although scientifically untested, urban expansion was deemed the cause and remedial measures were recommended by the Programa de Investigación en Desarrollo Humano Sostenible (ProDUS). CASC2D, a physically-based, spatially explicit hydrologic model, was constructed and calibrated to a June 10th 2002 storm that delivered 110.5 mm of precipitation in 4.5 h visibly exceeded the bankfull stage (0.9 m) of the Quebrada flooding portions of San Ramón. The calibrated hydrograph showed a peak discharge 16.68% (2.5 m³ s⁻¹) higher, an above flood stage duration 20% shorter, and time to peak discharge 11 min later than the same observed discharge hydrograph characteristics. Simulations of changing land cover conditions from 1979 to 1999 showed an increase also in the peak discharge, above flood stage duration, and time to peak discharge. Analysis using a modified location quotient identified increased urbanization in lower portions of the watershed over the time period studied. These results suggest that increased urbanization in the Quebrada Estero watershed have increased flooding peaks, and durations above threshold, confirming the ProDUS report. These results and the CASC2D model offer an easy-to-use, pragmatic planning tool for policymakers in San Ramón to assess future development scenarios and their potential flooding impacts to San Ramón.     

Book Reviews

Books reviewed:
Statistical Methods for Spatial Data Analysis by OLIVER SCHABENBERGER AND CAROL A GOTWAY. Chapman & Hall, Norwell, MA, 2005, 488 pp. ISBN 1-58488-322-7, $89.95.
Fuzzy Modeling with Spatial Information for Geographic Problems , edited by FEDERICK E PETRY, VINCENT B ROBINSON, AND MARIA A COBB. Springer, New York, 2005, 338 pp. ISBN 3-54023713-5, $92.00 (hardcover).
Statistical Analysis of Geographic Information with ArcView GIS® and ArcGIS® (Second Edition) by DAVID W S WONG AND JAY LEE. John Wiley and Sons, New York, 2005. 429 pp. ISBN 0-471-34874-0, $95.00 (cloth).     

Hard X-Ray Emission from the Galaxy Cluster A2256

After the positive detection by BeppoSAX of hard X-ray radiation up to approximately 80 keV in the Coma Cluster spectrum, we present evidence for nonthermal emission from A2256 in excess of thermal emission at a 4.6 sigma confidence level. In addition to this power-law component, a second nonthermal component already detected by ASCA could be present in the X-ray spectrum of the cluster, which is not surprising given the complex radio morphology of the cluster central region. The spectral index of the hard tail detected by the Phoswich Detection System on board BeppoSAX is marginally consistent with that expected for the inverse Compton model. A value of approximately 0.05 μG is derived for the intracluster magnetic field of the extended radio emission in the northern regions of the cluster, while a higher value of approximately 0.5 μG could be present in the central radio halo, which is likely related to the hard tail detected by ASCA.     

Exploring controls of the early and stepped deglaciation on the western margin of the British Irish Ice Sheet

New optically stimulated luminescence dating and Bayesian models integrating all legacy and BRITICE-CHRONO geochronology facilitated exploration of the controls on the deglaciation of two former sectors of the British–Irish Ice Sheet, the Donegal Bay (DBIS) and Malin Sea ice-streams (MSIS). Shelf-edge glaciation occurred ~27 ka, before the global Last Glacial Maximum, and shelf-wide retreat began 26–26.5 ka at a rate of ~18.7–20.7 m a^–1. MSIS grounding zone wedges and DBIS recessional moraines show episodic retreat punctuated by prolonged still-stands. By ~23–22 ka the outer shelf (~25 000 km²) was free of grounded ice. After this time, MSIS retreat was faster (~20 m a^–1 vs. ~2–6 m a^–1 of DBIS). Separation of Irish and Scottish ice sources occurred ~20–19.5 ka, leaving an autonomous Donegal ice dome. Inner Malin shelf deglaciation followed the submarine troughs reaching the Hebridean coast ~19 ka. DBIS retreat formed the extensive complex of moraines in outer Donegal Bay at 20.5–19 ka. DBIS retreated on land by ~17–16 ka. Isolated ice caps in Scotland and Ireland persisted until ~14.5 ka. Early retreat of this marine-terminating margin is best explained by local ice loading increasing water depths and promoting calving ice losses rather than by changes in global temperatures. Topographical controls governed the differences between the ice-stream retreat from mid-shelf to the coast.     

Using tree stems in multi-temporal terrestrial lidar scanning data to monitor landslides on vegetated slopes

Landslides - Terrestrial lidar scanning (TLS) has become a widely accepted expert tool for monitoring geohazards on bare or sparsely vegetated slopes through change detection. While trees can be an...     

Nonlinear behavior simulation of soil-structure interaction system via real-time hybrid testing

Bulletin of Earthquake Engineering - Soil-structure interaction (SSI) can potentially compromise structures that are subjected to seismic excitation. In recent years, real-time hybrid testing...     

GI Expertise

This article concerns the identification of the expertise that GI scientists have in common. Rather than attempt to be exhaustive, the approach is to identify a minimal set of expert topics shared across GI science. In this article, a set of five expert topics is proposed for this purpose: structure, uncertainty, dynamism, language and cognition, and design with geographic information. The article then examines the extent to which the literature lends support for these five topics, using two analyses: first, a qualitative analysis of the papers found in the 2006 Classics from IJGIS; and second a citation analysis investigating the occurrences of keywords related to the proposed expert topics. The results suggest that these five areas of expertise do indeed tend to distinguish research in GI science from that in other fields, and in particular where the expert topics occur in combination. The establishment of an acknowledged core of shared expertise should assist in interdisciplinary research and teaching collaboration, usually founded on a shared understanding of what expertise different partners can contribute.     

The diapcynal nutrient flux and shear-induced diapcynal mixing in the seasonally stratified western Irish Sea

We estimate the diapcynal nitrate flux in the seasonally stratified western Irish Sea using the dissipation method. By comparing the divergence of the reported benthic and diapcynal nitrate fluxes, we are able to explain much of the observed annual summer decline in deep-water nitrate at this location. We then show that the new production, fuelled by the diapcynal nitrate flux, is of a similar magnitude to that associated with the spring bloom. This suggests that the physical processes responsible for the diapcynal nitrate flux will set the limit on new production at this location. High-resolution mid-water column ADCP measurements show an average thermocline gradient Richardson number of 1, thus suggesting episodes of enhanced shear could result in shear instability, and therefore mixing within the thermocline. Bulk shear measurements reveal episodes of enhanced shear in the form of spikes, during which time the bulk shear vector takes the form of a clockwise rotating vector which has a period close to the local inertial period. The episodes of shear spikes are correlated to the wind and are consistent with observations made elsewhere. Estimates of profiles of the rate of dissipation of turbulent kinetic energy, based on microstructure velocity measurements, show that during a shear spike the dissipation rate within the thermocline, and therefore the buoyancy (and nitrate) flux, is enhanced by a factor of 4 when compared to periods with no shear spikes. Intermittent shear spikes are, therefore, an important mechanism for enhancing mixing across the shelf sea seasonal thermocline, and therefore delivery of nitrate to the euphotic zone, at this location.