Juan Restrepo - Academia.edu (original) (raw)

Papers by Juan Restrepo

Global and Planetary Change, 2006

The Magdalena, a world-class river, in the top ten in terms of sediment load~150 MT/yr, is the la... more The Magdalena, a world-class river, in the top ten in terms of sediment load~150 MT/yr, is the largest river discharging directly into the Caribbean Sea. Data on water discharge, sediment load, and dissolved load of the Magdalena River is presented as an initial interpretation of coastal ecosystems changes in relation to water discharge and sediment load from the Magdalena. During the 1972-1998 yr-period, the Magdalena River has delivered approximately 4022 MT of sediment to the Caribbean coast. The river reflects high inter-annual variability and delivers large portions of its fluvial discharge and sediment loads in short periods of time. The analysis of annual deviations from the 27-yr mean sediment load indicates that 59% of the total sediment load variability of the Magdalena at Calamar could be attributed to flashy peak events. Further analyses of sediment load anomalies suggest that there was a high discharge period in the Magdalena River between 1985 and 1995 and another one in the Canal del Dique between 1985 and 1992. These increasing trends in sediment load coincide with the overall decline of live coral cover around the Rosario Islands, a 145 km 2 coral reef complex in the Caribbean Sea that constitutes a marine protected area. The comparison of live coral: algae ratios for the 1983-2004 yr-period, also indicates that there has been an associated increase in the percentage of algae cover (i.e., Grande Island 1983 = 5%, 2004 = 59%). Other analyses show that nearly 850 ha of seagrass existing in the Cartagena Bay in the 1930s, only 76 ha remained in 2001, which is less than 8% of the original cover. There has been a mix of multiple stressors (natural and anthropogenic; local, regional and global; temporal and chronic) affecting the coastal ecosystems in the area, but the effect of the Magdalena River runoff has been constant and very prolonged (several decades). The impacts of heavy sediment loads and freshwater discharges from the Canal del Dique to Cartagena Bay have greatly contributed to the partial disappearance of coral formations and also to a considerable reduction in abundance of seagrass beds in the bay and neighboring areas. D

Journal of Geology, 2000

Small rivers draining high-rainfall basins and mountainous terrain west of the Cordilleras in Sou... more Small rivers draining high-rainfall basins and mountainous terrain west of the Cordilleras in South America have disproportionately high water discharge and sediment load. Fifteen rivers in western Colombia discharge a combined 254 km 3 yr Ϫ1 or 8020 m 3 s Ϫ1 of water into the Pacific. Sediment yield is strongly correlated with basin area ( 2 R = ), and sediment load is correlated with water discharge ( ). Rio San Juan occupies a 16,465-km 2 basin with 2 0.97 R = 0.73 a mean annual rainfall of 7277 mm. It has the highest water discharge (2550 m 3 s Ϫ1 ), sediment load ( t yr Ϫ1 ), 6 16 # 10 and basin-wide sediment yield (1150 t km Ϫ2 yr Ϫ1 ) on the entire west coast of South America. Rio Patía drains a 23,700km 2 basin with a mean annual rainfall of 2821 mm. Its water discharge, sediment load, and basin-wide sediment yield are 1291 m 3 s Ϫ1 , 14 t yr Ϫ1 , and 972 t km Ϫ2 yr Ϫ1 , respectively. Rio San Juan and Rio Patía deliver t of 6

Journal of Hydrology, 2006

The Magdalena River, a major fluvial system draining most of the Colombian Andes, has the highest... more The Magdalena River, a major fluvial system draining most of the Colombian Andes, has the highest sediment yield of any mediumsized or large river in South America. We examined sediment yield and its response to control variables in the Magdalena drainage basin based on a multi-year dataset of sediment loads from 32 tributary catchments. Various morphometric, hydrologic, and climatic variables were estimated in order to understand and predict the variation in sediment yield. Sediment yield varies from 128 to 2200 t km K2 yr K1 for catchments ranging from 320 to 59,600 km 2 . The mean sediment yield for 32 sub-basins within the Magdalena basin is w690 t km K2 yr K1 . Mean annual runoff is the dominant control and explains 51% of the observed variance in sediment yield. A multiple regression model, including two control variables, runoff and maximum water discharge, explains 58% of the variance. This model is efficient (MEZ0.89) and is a valuable tool for predicting total sediment yield from tributary catchments in the Magdalena basin. Multiple correlations for those basins corresponding to the upper Magdalena, middle basin, Eastern Cordillera, and catchment areas greater than 2000 km 2 , explain 75, 77, 89, and 78% of the variance in sediment yield, respectively. Although more variance is explained when dataset are grouped into categories, the models are less efficient (ME!0.72). Within the spatially distributed models, six catchment variables predict sediment yield, including runoff, precipitation, precipitation peakedness, mean elevation, mean water discharge, and relief. These estimators are related to the relative importance of climate and weathering, hillslope erosion, and fluvial transport processes. Time series analysis indicates that significant increases in sediment load have occurred over 68% of the catchment area, while 31% have experienced a decreasing trend in sediment load and thus yield. Land use analysis and increasing sediment load trends indicate that erosion within the catchment has increased over the last 10-20 years. q

Physica D-nonlinear Phenomena, 2004

Siam Journal on Scientific Computing, 1998

An application of Pontryagin's maximum principle data assimilation is used to blend possibly inco... more An application of Pontryagin's maximum principle data assimilation is used to blend possibly incomplete or nonuniformly distributed spatio-temporal observational data into geophysical models. Used extensively in engineering control theory applications, data assimilation has been introduced relatively recently into meteorological forecasting, natural-resource recovery modeling, and climate dynamics.

Journal of Fluid Mechanics, 2002

The lift and drag forces on an isolated particle resulting from an oscillating wallbounded flow, ... more The lift and drag forces on an isolated particle resulting from an oscillating wallbounded flow, are approximated using direct numerical simulation and extrapolation techniques. We also confirm the existence of anomalies in the lift force, which arise from the interaction of the vortical field with the particle. Anomalies can also occur for computational reasons and these are discussed as well.

Journal of Computational Physics, 1995

The relative merits of the wavelet-Galerkin solution of hyperbolic partial di erential equations,... more The relative merits of the wavelet-Galerkin solution of hyperbolic partial di erential equations, typical of geophysical problems, are quantitatively and qualitatively compared to traditional nite di erence and Fourier-pseudo-spectral methods. The wavelet-Galerkin solution presented here is found to be a viable alternative to the two conventional techniques.

Physica D-nonlinear Phenomena, 2004

Siam Journal on Scientific Computing, 1998

International Journal for Numerical Methods in Engineering, 1997

Inner products of wavelets and their derivatives are presently known as connection coe cients. Th... more Inner products of wavelets and their derivatives are presently known as connection coe cients. The numerical calculation of inner products of periodized Daubechies wavelets and their derivatives is reviewed, with the aim at providing potential users of the publicly-available numerical scheme, details of its operation. The numerical scheme for the calculation of connection coe cients is evaluated in the context of approximating di erential operators, information which is useful in the solution of partial di erential equations using wavelet-Galerkin techniques. Speci c details of the periodization of inner products in the solution di erential equations are included in the presentation.