Generating MODFLOW grids from boundary representation solid models

Complex stratigraphy can be difficult to simulate in MODFLOW models. MODFLOW uses a structured grid that requires that each grid layer be continuous throughout the model domain. This makes it difficult to explicitly represent common features such as pinchouts and embedded seams in a MODFLOW model. In this paper, we describe a method for automatically generating MODFLOW-compatible grids from boundary-representation solid models. Solid models are data structures developed originally for computer-aided design applications that define the geometry of three-dimensional objects. Solid models can be used to represent arbitrarily complex stratigraphy. The elevations defined by the solids are then extracted from the solids in a manner that preserves the continuous-layer requirement imposed by MODFLOW. Two basic approaches are described: The first method adjusts the MODFLOW grid dimensions (layer elevations) to fit the solid model boundaries, and the second method creates a regular MODFLOW grid and adjusts the material properties to match the changes in stratigraphy. One of the main benefits of using solid models to define stratigraphy for MODFLOW models is that it provides a grid-independent definition of the layer elevations that can be used to immediately re-create the MODFLOW grid geometry after any change to the grid resolution.     

Comparison of TRMM and water district rain rates over New Mexico

This paper compares monthly and seasonal rain rates derived from the Version 5 (V5) and Version 6 (V6) TRMM Precipitation Radar (TPR, TSDIS reference 2A25), TRMM Microwave Imager (TMI, 2A12), TRMM Combined Instrument (TCI, 2B31), TRMM calibrated IR rain estimates (3B42) and TRMM merged gauge and satellite analysis (3B43) algorithms over New Mexico (NM) with rain gauge analyses provided by the New Mexico water districts (WD). The average rain rates over the NM region for 1998–2002 are 0.91mmd?1 for WD and 0.75, 1.38, 1.49, 1.27, and 1.07mmd?1 for V5 3B43, 3B42, TMI, PR and TCA; and 0.74, 1.38, 0.87 and 0.97 mm d?1 for V6 3B43, TMI, TPR and TCA, respectively. Comparison of V5 3B43 with WD rain rates and the daily TRMM mission index (TPR and TMI) suggests that the low bias of V5 3B43 for the wet months (summer to early fall) may be due to the non-inclusion of some rain events in the operational gauge analyses that are used in the production of V5 3B43. Correlation analyses show that the WD rain rates vary in phase, with higher correlation between neighboring WDs. High temporal correlations (>0.8) exist between WD and the combined algorithms (3B42, 3B43 and TCA for both V5 and V6) while satellite instrument algorithms (PR, TMI and TCI) are correlated best among themselves at the monthly scale. Paired t-tests of the monthly time series show that V5 3B42 and TMI are statistically different from the WD rain rates while no significant difference exists between WD and the other products. The agreements between the TRMM satellite and WD gauge estimates are best for the spring and fall and worst for winter and summer. The reduction in V6 TMI (?7.4%) and TPR (?31%) rain rates (compared to V5) results in better agreement between WD estimates and TMI in winter and TPR during summer.     

Modeling the Usefulness of Spatial Correlation Analysis on Karst Systems

Cross-correlation analyses on field data collected in karst aquifer systems can be used to develop a conceptual understanding of the aquifer. This includes the use of many data sets from the same aquifer to develop an understanding of how properties vary spatially. We focus on a method for characterizing the distribution of recharge, which is becoming increasingly important in regions where urban development encroaches on these important sources of water. Spatially varying precipitation data and cross-correlation analysis provide a means of spatially characterizing recharge locations on a karst aquifer. Our work expands on the numerical experiments conducted by Padilla and Pulido-Bosch (1995) using the numerical ground water model MODFLOW to introduce spatially varying parameters. The numerical experiments include conduit-controlled, matrix-controlled, and mixed karst systems with more than one precipitation time series input. The results show that spatially varying parameters can be inferred based on the cross-correlation of precipitation data and spring discharge. Simulations were completed using aquifer parameters derived from studies of the Barton Springs segment of the Edwards Aquifer. The simulations indicate that spatial variability within an aquifer can be inferred using cross-correlation analysis. A field study using these methods is summarized for Barton Springs near Austin, Texas.     

Fatty acid composition of phytoplankton, settling particulate matter and sediments at a sheltered bivalve aquaculture site

Fatty acid biomarkers were used to investigate the biogeochemistry of a former blue mussel (Mytilus edulis) aquaculture site in a shallow, sheltered cove in northeastern Newfoundland. High levels of polyunsaturated fatty acids (PUFA) in net-tow and sediment trap samples indicated a substantial phytoplankton source of organic matter, and fluctuations in specific fatty acid biomarkers reflected the changing abundances of diatoms and dinoflagellates. In comparison, sediments contained very low levels of PUFA (<15%) and were dominated by terrestrial and bacterial markers. In a separate study, blue mussels were grown at this closed site, providing the opportunity to examine the relationship between lipid supply, as recorded by net-tow and trap samples, and bivalve requirements. The average plankton fatty acid composition throughout the year agreed well with that of the adult blue mussels, suggesting that fatty acids were provided in proportions very similar to the bivalves' requirements. The fatty acid composition of the blue mussels was typical of those collected elsewhere, with PUFA proportions near 50%. However, examination of fatty acid data of plankton sampled in other areas revealed that the plankton in the current study may have been unusual in providing fatty acids at levels required by the bivalves.     

Topographical distribution of lipids inside the mandibular fat bodies of odontocetes: remarkable complexity and consistency

Odontocetes possess unusual and specialized mandibular fat bodies in and around their lower jaws. These tissues have been proposed to facilitate sound reception and are composed of unusual endogenously synthesized lipids. Little is known about how the topographical arrangement of the lipid molecules in these tissues influences sound reception. We examined the lipid composition of the mandibular fat bodies, using a fine-scale approach, on six specimens (representing four odontocete families). We show that odontocete jaw lipids exhibit a complex structural three-dimensional topography. Different odontocetes synthesize and deposit slightly different molecules, but the relative arrangement of the lipids within each head showed marked consistency. Mandibular fats of beaked whales were uniquely dominated by isolauric acid (i-12:0). In contrast, the dolphin and porpoise biosynthesized isovaleric acid (i-5:0), while the pygmy sperm whale deposited medium-length (10-14 carbons) straight-chain lipids. In all heads examined, the shortest and branched-chain ("i") fatty acids were concentrated in the center of the jaw fats, which connect intimately with the ears. We hypothesize that in odontocete jaws, this arrangement may serve to channel an incoming sound to the ears because sound travels slower through shorter branched-chain fatty acids than through longer straight-chain fatty acids.     

Making in the City: disjunctures between public discourse and urban policy

Creative cities contribute much to the cultural economies and identities of a nation, shaping imagination and talent, and contributing to the sense of livability and place. Artists, designers, crafters, tinkerers, and even small-scale manufacturers are at the heart of urban rejuvenation in cities such as Brooklyn in New York, and Newcastle and Melbourne in Australia. Increasingly this activity is referred to in the public realm via the media, including social media, through the all-encompassing term ‘making’. Yet in much public policy, this activity is framed through previously held notions: artists, culture, and the precincts associated with this life. I explore this disjuncture by focusing on a case study of Australia’s largest city, Sydney, to interrogate the current schism between public and policy discourse. I share findings about the role of discourse, community consultation, and timing in policy development to argue that valuing making in cities requires commitment to continual community consultation to ensure policy currency, with makers as key stakeholders in this dialogue. Furthermore, the intersection of policy domains is required to prevent isolating making into one policy area. I highlight implications for the imagining of creative cities.     

Transient events in the COBE database simultaneous with gamma ray bursts

We are investigating the COBE DMR data at instances of known -ray bursts (GRBs) when any of the six DMR horn directions was coincident with the direction of a burst. The BATSE instrument on board GRO has detected 207 bursts during the eight-month period of overlap corresponding to the current release of COBE data. The odds of a GRB occurring within the DMR field of view are near one coincidence per year. Here we report on one such serendipitous observation in 1991, GRB 911226, for which a detailed analysis is currently in progress.     

A catchment scale evaluation of the SIBERIA and CAESAR landscape evolution models

Landscape evolution models provide a way to determine erosion rates and landscape stability over times scales from tens to thousands of years. The SIBERIA and CAESAR landscape evolution models both have the capability to simulate catchment–wide erosion and deposition over these time scales. They are both cellular, operate over a digital elevation model of the landscape, and represent fluvial and slope processes. However, they were initially developed to solve research questions at different time and space scales and subsequently the perspective, detail and process representation vary considerably between the models. Notably, CAESAR simulates individual events with a greater emphasis on fluvial processes whereas SIBERIA averages erosion rates across annual time scales. This paper describes how both models are applied to Tin Camp Creek, Northern Territory, Australia, where soil erosion rates have been closely monitored over the last 10 years. Results simulating 10 000 years of erosion are similar, yet also pick up subtle differences that indicate the relative strengths and weaknesses of the two models. The results from both the SIBERIA and CAESAR models compare well with independent field data determined for the site over different time scales. Representative hillslope cross‐sections are very similar between the models. Geomorphologically there was little difference between the modelled catchments after 1000 years but significant differences were revealed at longer simulation times. Importantly, both models show that they are sensitive to input parameters and that hydrology and erosion parameter derivation has long‐term implications for sediment transport prediction. Therefore selection of input parameters is critical. This study also provides a good example of how different models may be better suited to different applications or research questions. Copyright © 2010 John Wiley & Sons, Ltd and Commonwealth of Australia