Quantifying terrain controls on runoff retention and routing in the Northern Prairies

The role of hummocky terrain in governing runoff routing and focussing groundwater recharge in the Northern Prairies of North America is widely recognised. However, most hydrological studies in the region have not effectively utilised information on the surficial geology and associated landforms in large-scale hydrological characterization. The present study uses an automated digital elevation model (DEM) analysis of a 6500-km² area in the Northern Prairies to quantify hydrologically relevant terrain parameters for the common types of terrains in the prairies with different surficial deposits widespread in the prairies, namely, moraines and glaciolacustrine deposits. Runoff retention (and storage) capacity within depressions varies greatly between different surficial deposits and is comparable in magnitude with a typical amount of seasonal snowmelt runoff generation. The terrain constraint on potential runoff retention varies from a few millimetres in areas classified as moraine to tens of millimetres in areas classified as stagnant ice moraine deposits. Fluted moraine and glaciolacustrine deposits have intermediate storage capacity values. The study also identified the probability density function describing a number of immediate upstream neighbours for each depression in a fill-and-spill network. A relationship between depression parameters and surficial deposits, as well as identified depression network structure, allows parametrisation of hydrologic models outside of the high-resolution DEM coverage, which can still account for terrain variation in the Prairies.     

On the testing of fully integrated surface–subsurface hydrological models

Studies employing integrated surface–subsurface hydrological models (ISSHMs) have utilized a variety of test cases to demonstrate model accuracy and consistency between codes. Here, we review the current state of ISSHM testing and evaluate the most popular ISSHM test cases by comparing the hydrodynamic processes simulated in each case to the processes found in well‐characterized, real‐world catchments and by comparing their general attributes to those of successful benchmark problems from other fields of hydrogeology. The review reveals that (1) ISSHM testing and intercode comparison have not adopted specific test cases consistently; (2) despite the wide range of ISSHM metrics available for model testing, only two model performance diagnostics are typically adopted: the catchment outflow hydrograph and the catchment water balance; (3) in intercode comparisons, model performance is usually judged by evaluating only one performance diagnostic: the catchment outflow hydrograph; and (4) ISSHM test cases evaluate a small number of hydrodynamic processes that are largely uniform across the model domain, representing a limited selection of the processes of interest in well‐characterized, real‐world catchments. ISSHM testing would benefit from more intercode comparisons using a consistent set of test cases, aimed at evaluating more catchment processes (e.g. flooding) and using a wider range of simulation diagnostics (e.g. pressure head distributions). To achieve this, a suite of test case variations is required to capture the relevant catchment processes. Finally, there is a need for additional ISSHM test problems that compare model predictions with hydrological observations from intensively monitored field sites and controlled laboratory experiments. Copyright © 2012 John Wiley & Sons, Ltd.     

Delta spots and great flares

Solar Physics - Using eighteen years of observations at Big Bear, we summarize the development of δ spots and the great flares they produce. We find δ groups to develop in three ways:...     

Naked sunspots

Naked sunspots are spots seen in Hα to be devoid of associated plage. In magnetograms and K-line little if any opposite polarity field is found, and in soft X-ray images a blank appears in the region of the spot. In almost all cases studied in which naked spots resulted the spot groups had emerged in unipolar regions of the same polarity as the naked spot. At least half of the naked spots are associated with coronal holes. The naked spots are long-lived and show rotation rates close to the Newton-Nunn curve. Most of the naked spots had bright rims in Hα, and the one spot observed to disappear left no trace in the background magnetic field. These spots may be a means by which separation of p from f magnetic polarity occurs.     

Delta spots and great flares

Using eighteen years of observations at Big Bear, we summarize the development of δ spots and the great flares they produce. We find δ groups to develop in three ways: eruption of a single complex active region formed below the surface, eruption of large satellite spots near (particularly in front of) a large older spot, or collision of spots of opposite polarity from different dipoles. Our sample of twenty-one δ spots shows that once they lock together, they never separate, although rarely an umbra is ejected. The δ spots are already disposed to their final form when they emerge. The driving force for the shear is spot motion, either flux emergence or the forward motion of p spots in an inverted magnetic configuration. We observe the following phenomena preceding great flares:

1. δ spots, preferentially Types 1 and 2.
2. Umbrae obscured by Hα emission.
3. Bright Hα emission marking flux emergence and reconnection.
4. Greatly sheared magnetic configurations, marked by penumbral and Hα fibrils parallel to the inversion line.

We assert that with adequate spatial resolution one may predict the occurrence of great flares with these indicators.     

Evaluating the sensitivity of DRASTIC using different data sources,interpretations and mapping approaches

When used in a comprehensive risk assessment framework, aquifer vulnerability maps are a tool to identify the relative susceptibility of the groundwater from sources of contamination at the land surface. The DRASTIC method was designed for use over large areas with a wide variety of geological and hydrogeologic settings as a screening tool in groundwater protection and management. In this study, a series of vulnerability maps were made for the Greater Oliver area, in south central Okanagan, British Columbia, Canada, to test the sensitivity of the methodology to changes in input data type, interpretation, and mapping approaches. The study also illustrates how DRASTIC can be modified for use in areas of limited geological variability, where it may be important for smaller-scale changes in vulnerability to be recognized. Maps were produced using the original DRASTIC rating tables, a set of expanded tables using the original properties but modified ranges to accommodate the variability of data in the valley bottom region, and alternate tables, with modified properties and ranges. Differences in vulnerability rating for the maps using selected combinations and data interpretations are compared to the map using original DRASTIC rating tables using visual and statistical methods. One map was generated using expert hydrological knowledge. The modified tables allowed a greater amount of variability to be expressed in the valley bottom area compared to using the original tables and methods, and could provide a reasonable approach for assessing local scale variability for source water protection planning.     

Comparing approaches for modeling spatially distributed direct recharge in a semi-arid region (Okanagan Basin, Canada)

Spatially distributed recharge is compared at two different scales using three different modeling approaches within the semi-arid Okanagan Basin, British Columbia, Canada. Regional recharge was modeled by mapping results for one-dimensional soil columns from the water-balance code HELP (Hydrologic Evaluation of Landfill Performance, V3.80D). The regional model was then compared to two, independently derived, local-scale models to ensure local trends were captured in the regional model, and to compare modeling methods. Average annual recharge, predicted by the regional model, varied from no recharge to 186 mm/yr. For the north Okanagan (Vernon area), regional estimates were compared to Richards’ equation-based MIKE-SHE (V2007) estimates, which showed a significant difference in average annual recharge: 7 mm/yr (MIKE-SHE) and 109 mm/yr (HELP). In the south Okanagan (Oliver area), regional estimates were compared to high-resolution, local HELP estimates. Similar values of average annual recharge were obtained: 34 mm/yr (local) and 42 mm/yr (regional). A comparison with measured actual evapotranspiration data in the north Okanagan, showed HELP over-predicted recharge compared to MIKE-SHE by under-predicting evapotranspiration during summer months. Thus, the use of HELP in semi-arid areas may be limited if accurate estimates of recharge are needed. However, results may give satisfactory groundwater model calibrations results because of high uncertainty in hydraulic properties.     

Emerging flux in active regions

We have compared the rates at which flux emerges in active and quiet solar regions within the sunspot belts. The emerging flux regions (EFRs) were identified by the appearance of arch filament structures in H. All EFRs in high-resolution films of active regions made at Big Bear in 1978 were counted. The comparable rate of flux emergence in quiet regions was obtained from SGD data and independently from EFRs detected outside the active region perimeter on the same films. The rate of flux emergence is 10 times higher in active regions than in quiet regions. A sample of all active regions in 31 days of 1983 gave a ratio of 7.5. We discuss possible mechanisms which might funnel new magnetic flux to regions of strong magnetic field.     

Boundary integral equation solutions for solitary wave generation, propagation and run-up

The boundary integral equation method (BIEM) is developed as a tool for studying two-dimensional, nonlinear water wave problems, including the phenomena of wave generation, propagation and run-up. The wave motions are described by a potential flow theory. Nonlinear free-surface boundary conditions are incorporated in the numerical formulation. Examples are given for either a solitary wave or two successive solitary waves. Special treatment is developed to trace the run-up and run-down along a shoreline. The accuracy of the present scheme is verified by comparing numerical results with experimental data of maximum run-up.