Permeability of Parkia gigantocarpa as affected by wood anatomy

This study evaluated Parkia gigantocarpa wood from the Amazon rainforest for its permeability to air and liquid in the longitudinal direction. The influence of anatomical characteristics on the permeability of wood was characterized. Three trees were collected in the State of Pará, Brazil. Samples were converted into specimens and subjected to permeability tests and anatomical characterization. Permeability was obtained in the laboratory, and the results were compared with the permeability data estimated by a longitudinal flow model for hardwoods. The air permeability of wood was 140.2 x 10-9 m3.[m.(N.m-2).s]-1 liquid permeability was 3.28 x 10-9 m3.[m.(N.m-2).s]-1. The fiber length and thickness of the cell wall had a direct and positive relationship with the permeability, whereas fiber width presented an inverse relationship with permeability. The vessel frequency and diameter did not influence the permeability of wood from the heartwood of P. gigantocarpa that presented high permeability and potential for easy wood drying and treatment.

NUMERICAL SIMULATION OF MUDFLOW WITH A TWO-DIMENSIONAL DEPTH-AVERAGED MODEL

This study is motivated by the need to mitigate damages caused by mudflow disaster, which is occurring frequently due to intensive forest clearing and uncontrolled land use at highland. Numerical modelling of mudflow is challenging as the propagation speed and rheological behavior of the flow relies on the accuracy of the numerical scheme and choice of rheological model. In this study, a two-dimensional depth-averaged model was developed to simulate a simplified mudflow event. In order to capture shock in mudflow, the finite volume method (FVM) with third order accurate Monotonic Upstream-centered Scheme of Conservation Laws (MUSCL) scheme was adopted in the numerical model and the model was verified against a benchmark partial dam-break problem. By assuming that the mudflow has high amount of fine mud suspension. the rheological model was represented by a simplified Herschel-Bulkley model. Numerical results showed that the Herschel-Bulkley model could reproduce the viscoplastic behavior of mudflow well, especially in the estimation of final longitudinal flow spreading (2% difference compared to experimental value) and depth of peak wave (8.8% maximum difference). The robustness and stability of the model was demonstrated by simulating a simplified mudflow event with obstacles.

Two-dimensional liquid water flow through snow at the plot scale in continental snowpacks: simulations and field data comparisons

Modeling the multidimensional flow of liquid water through snow has been limited in spatial and temporal scales to date. Here, we present simulations using the inverse TOUGH2 (iTOUGH2) model informed by the model SNOWPACK, referred to as SnowTOUGH. We use SnowTOUGH to simulate snow metamorphism, melt/freeze processes, and liquid water movement in two-dimensional snowpacks at the plot scale (20 m) on a sloping ground surface during multi-day observation periods at three field sites in northern Colorado, USA. Model results compare well with sites below the treeline and above the treeline but not at a site near the treeline. Results show the importance of longitudinal intra-snowpack flow paths (i.e., parallel to ground surface in the downslope direction and sometimes referred to as lateral flow), particularly during times when the snow surface (i.e., snow–atmosphere interface) is not actively melting. At our above-treeline site, simulations show that longitudinal flow can occur at rates orders of magnitude greater than vertically downward percolating water flow at a mean ratio of 75:1 as a result of hydraulic barriers that divert flow. Our near-treeline site simulations resulted in slightly less longitudinal flow than vertically percolating water, and the below-treeline site resulted in negligible longitudinal flow of liquid water. These results show the increasing influence of longitudinal intra-snowpack flow paths with elevation, similar to field observations. Results of this study suggest that intra-snowpack longitudinal flow may be an important process for consideration in hydrologic modeling for higher-elevation headwater catchments.

The Response of Lateral Flow to Peak River Discharge in a Macrotidal Estuary

The Ou River, a medium-sized river in southeastern China, is selected to study the lateral flow response to rapidly varied river discharge, i.e., peak river discharge (PRD). A three-dimensional model based on the Finite-Volume Community Ocean Model is validated by in situ measurements from 15 June to 16 July 2005. PRD, which considers the extra buoyancy and longitudinal momentum in a short time, rebuilds the stratification and lateral flow. PRD, compared with low-discharge, generally makes stratification stronger and lateral flow weaker. PRD mainly rebuilds lateral flow by changing lateral advection, lateral Coriolis, and lateral-barotropic pressure gradient terms. After PRD, the salinity recovery time is longer than that of the flow because the impact on buoyancy lasts longer than that on longitudinal flow. Longitudinal flow is mostly affected by the momentum transferred during PRD; therefore, the recovery time is close to the flooding duration. However, the lateral flow is affected by the buoyancy, and its recovery time is generally longer than the flooding duration. The lateral flow recovery time depends on transect width, flow velocity and the variation caused by PRD. PRD occurs widely in global small-/medium-sized river estuaries, and the result of this work can be extended to other estuaries.