Mild Slope Research Articles

A 2DH nonlinear Boussinesq-type wave model of improved dispersion, shoaling, and wave generation characteristics

A modified Boussinesq-type model is derived to account for the propagation of either regular or irregular waves in two horizontal dimensions. An improvement of the dispersion and shoaling characteristics of the model is obtained by optimizing the coefficients of each term in the momentum equation, expanding in this way its applicability in very deep waters and thus overcoming a shortcoming of most models of the same type. The values of the coefficients are obtained by an inverse method in such a way as to satisfy exactly the dispersion relation in terms of both first and second-order analyses matching in parallel the associated shoaling gradient. Furthermore a physically more sound way to approach the evaluation of wave number in irregular wave fields is proposed. A modification of the wave generator boundary condition is also introduced in order to correctly simulate the phase celerity of each input wave component. The modified model is applied to simulate the propagation of breaking and non-breaking, regular and irregular, long and short crested waves in both one and two horizontal dimensions, in a variety of bottom profiles, such as of constant depth, mild slope, and in the presence of submerged obstacles. The simulations are compared with experimental data and analytical results, indicating very good agreement in most cases.

Environmental cues for mass nesting of sea turtles

Mass nesting of Olive Ridley sea turtles at Rushikulya rookery exhibit interannaul variability in population size as well as location of nesting site. This year mass nesting was observed over sand spit (0.25 million) and sporadic nesting (0.05 million) at the rookery and the nesting population surpassed all previous records. The present study examines multiple environmental cues (beach width, volume, shoreline change, foreshore slope, sediment grain size, littoral environmental observation, wind speed and direction) during mass nesting events to assess the factor(s) which favour mass nesting and also the reasons for the record mass nesting over a new site (sand spit). Analysis of results indicates that beach/spit to the north of the river mouth with medium width, mild slope and medium sand grain is a favoured location for mass nesting. Near shore oceanographic conditions conducive for mass nesting are low saline near shore surface water, low energy and relatively longer period south southeasterly waves. Local wind burst with a few days lag/lead of the new/full moon appears as one of the most important factors which trigger mass nesting. Environmental cues for selection of mass nesting site and the factor triggering the mass nesting revealed in the present study are of paramount importance for rookery management and conservation of the vulnerable sea turtles.

Steps of fitting the winter shelter of Hungarian Grey Cattle into the environment in Ipolyvece

Besides creating a living place satisfying the unique demands of Hungarian grey cattle the planning of a winter shelter constructed in Ipolyvece (Ipolyvece Farm) has raised exceptionally diverse tasks as regards of fitting the shelter into the environment. This article introduces the different versions of related demands and answers as well as the finally approved solutions which have been created by using - due to necessity - the „research by planning” methodology. The facility has been constructed for the winter housing of those cattle and their offsprings that live in and around the municipal area of Ipolyvece, i.e. in the alluvial pastures of the Ipoly river during the growing season (from April until the end of October). The area involved in the planning process includes some plots and buildings of an animal husbandry facility built in the early 1960s. These real estates have been detached from the other parts of the farm and given to the current operator as a result of the privatisation process of the early 1990s. The installations are situated in the mild North-western slope of Börzsöny mountains. This slope is bounded by a railroad embankment running around the built-up area of the settlement. The embankment is perpendicular to the slope thus creating a valley where the runoff of water is not ensured. A particularly sensitive groundwater supply can be found below the area; this fact makes special protective measures necessary in order to restrain the utilisation and environmental impact of the surface area.

Numerical simulations of comminution slurries over complex topographies: Putting together CFD and pipeline integrity

The use of computational fluid dynamics gives new and interesting insights for risk analysis of cross-country ore hydraulic transport operations. In particular, they offer the possibility to predict, with reasonable accuracy, the progression and final condition of spills driven by pipeline leaks at selected locations, at a relatively modest computational cost. In this work, a depth-averaged, two-dimensional numerical model is used to simulate an ore concentrate pipeline rupture and subsequent spill, reproduced as a constant flow condition at the leak point. Although the model is well suited to solve the governing flow equations on arbitrary topographies by means of digital elevation models, two specific locations featuring relatively mild and steep slopes, are analysed with regard to their implications on the potential requirements for emergency team response. Results, obtained using different slurry rheologies, are compared with those obtained using a simpler, common flow resistance model derived for water flowing over rough surfaces.

Intermediate-scale analysis of landscape characteristics affecting edge formation in burned forests in Samcheok, Korea

Compared to burn interiors, edges exhibit distinct biotic and abiotic conditions that include microclimate, wind speed, sunlight levels, soil composition, moisture content, nutrient availability, population density, and species diversity. This study characterized the landscapes in which burned forest edges formed in Samcheok, Korea. Over the study area, 500-m2 grid cells were generated to capture landscape characteristics. Grid cells intersecting burn boundary lines were designated as edge, while cells without these lines were classified as the interior of burned areas. Topographic variables including slope, elevation, topographic wetness index, solar radiation index, and proportions of fuel and land use types within grid cells were computed in a geographical information system (GIS). Correlation analysis with modified t-test and regression tree analysis were performed to explore the influences of landscape variables on edge formation with avoiding spatial autocorrelation problems. The results indicated that edges formed at low elevations with mild slopes, high topographic wetness, and low solar radiation. Edges were unlikely to form in areas dominated by Japanese red pines at low elevations. Moreover, heterogeneous land use/cover types contributed significantly to edge formation. Different forest management strategies for different landscape conditions can be more effective for enhancing resilience of forests to fire. Reducing susceptible fuel types might be effective at low elevations, while enhancing forest heterogeneity might be more effective at high elevations.

A Numerical Implementation of a Nonlinear Mild Slope Model for Shoaling Directional Waves

We describe the numerical implementation of a phase-resolving, nonlinear spectral model for shoaling directional waves over a mild sloping beach with straight parallel isobaths. The model accounts for non-linear, quadratic (triad) wave interactions as well as shoaling and refraction. The model integrates the coupled, nonlinear hyperbolic evolution equations that describe the transformation of the complex Fourier amplitudes of the deep-water directional wave field. Because typical directional wave spectra (observed or produced by deep-water forecasting models such as WAVEWATCH III™) do not contain phase information, individual realizations are generated by associating a random phase to each Fourier mode. The approach provides a natural extension to the deep-water spectral wave models, and has the advantage of fully describing the shoaling wave stochastic process, i.e., the evolution of both the variance and higher order statistics (phase correlations), the latter related to the evolution of the wave shape. The numerical implementation (a Fortran 95/2003 code) includes unidirectional (shore-perpendicular) propagation as a special case. Interoperability, both with post-processing programs (e.g., MATLAB/Tecplot 360) and future model coupling (e.g., offshore wave conditions from WAVEWATCH III™), is promoted by using NetCDF-4/HD5 formatted output files. The capabilities of the model are demonstrated using a JONSWAP spectrum with a cos2s directional distribution, for shore-perpendicular and oblique propagation. The simulated wave transformation under combined shoaling, refraction and nonlinear interactions shows the expected generation of directional harmonics of the spectral peak and of infragravity (frequency <0.05 Hz) waves. Current development efforts focus on analytic testing, development of additional physics modules essential for applications and validation with laboratory and field observations.

Go with the flow: geospatial analytics to quantify hydrologic landscape connectivity for passively dispersed microorganisms

Understanding the diverse ways that landscape connectivity influences the distribution of microbial species is central to managing the spread and persistence of numerous biological invasions. Here, we use geospatial analytics to examine the degree to which the hydrologic connectivity of landscapes influences the transport of passively dispersed microbes, using the invasive plant pathogen Phytophthora ramorum as a case study. Pathogen occurrence was analyzed at 280 stream baiting stations across a range of watersheds – exposed to variable inoculum pressure – in California over a 7-year period (2004–2010). Using logistic regression, we modeled the probability of pathogen occurrence at a baiting station based on nine environmental variables. We developed a novel geospatial approach to quantify the hydrologic connectivity of host vegetation and inoculum pressure derived from least cost distance analyses in each watershed. We also examined the influence of local environmental conditions within the immediate neighborhood of a baiting station. Over the course of the sampling period, the pathogen was detected at 67 baiting stations associated with coastal watersheds with mild climate conditions, steep slopes, and higher levels of inoculum pressure. At the watershed scale, hydrologic landscape connectivity was a key predictor of pathogen occurrence in streams after accounting for variation in climate and exposure to inoculum. This study illustrates a geospatial approach to modeling the degree to which hydrologic systems play a role in shaping landscape structures conducive for the transport of passively dispersed microbes in heterogeneous watersheds.

Effects of tillage practices on nutrient loss and soybean growth in red-soil slope farmland

Field experiments were conducted to examine the effect of tillage practices on sediment and nutrient loss and soybean growth under natural rainfall conditions. Three tillage practices were applied: downslope ridge (check) ,downslope ridge + contour living hedgerow,and cross ridge. Cross ridge tillage reduced surface runoff by 69% and sediment yield by 86% ,compared to the check treatment. The downslope ridge with a contour living hedgerow reduced surface runoff by 24% and sediment yield by 53% . Additionally,compared to the check plot ,nutrient losses carried by runoff were reduced by over 68% and that carried in the sediment was reduced more than 85% in the cross ridge plot. Nutrient losses in runoff were reduced by 20% to 30% in the downslope ridge and contour living hedgerow plot and those carried in the sediment were reduced by 44% to 57% . Cross ridge tillage soybean yields exceeded those of the downslope ridge and downslope ridge + contour living hedgerow treatments by 16% – 18% . Cross ridge tillage could contribute to the prevention sediment and nutrient loss and could improve crop yield, and thus it is recommended to be applied to mild slopes in the red soil region.

Experimental Study on Backwater in Cavity of Aerator on Chute with Mild Slope

Aerator is often used in the spillways or tunnels to protect these discharge release works from cavitation damage. But for the flow chutes with mild bottom slope, the backwater may occur easily in the aerators cavity. There are a lot of factors to influence the backwater in the cavity. Based on the model experiments and analysis, the backwater in the bottom aerators cavity on the chutes with mild bottom slope and some influence factor to the backwater are investigated. The research presented in this paper provides some laws of how backwater exists in the aerators cavity and how to reduce backwater in the cavity. Results show, in the case of other conditions remain unchanged, flow discharge is inversely proportion to the depth of backwater, and the takeoff angle of aerator affects the depth of backwater larger than the slope of chute; the greater the flow discharge is, the lower the depth of backwater. And the depth of backwater increases with aerator height. More attention should be paid to the backwater in the cavity for the chute with small bottom slope.

Application of a Nonlinear Elliptic Mild Slope Equation in Rizhao Harbor

A nonlinear elliptic mild slope equation was used to simulate the wave transformation in the water of Rizhao harbor. The model is well suited to complex domain, and fits the irregular boundary conveniently. When the incident direction of wave is E, the mooring condition of harbor entrance is poor, and when the incident direction is SE, the wave hights are relatively great in the inside harbor basin. In wave numerical simulation, the physical phenomenon of wave transformation including wave diffraction, refraction and reflection can be shown obviously. The results show that the model could be used on relative large region and get ideal results.

Numerical simulation of wave-induced morphology evolution

This paper presents an integrated coastal engineering numerical model. The model simulates the linear wave propagation, wave-induced circulation, sediment transport and bed morphology evolution. The model consists of three main modules: Wave-LS, Wave-L and Coast. The large-scale module Wave-LS is based on the numerical solution of the directional wave energy balance equation. The near-shore wave transformation module Wave-L is based on the hyperbolic-type mild slope equation and is valid for a compound wave field near coastal structures where the waves are subjected to the combined effects of shoaling, refraction, diffraction, reflection (total and partial) and breaking. Radiation stress components (estimated from the large-scale module as well as from the hyperbolic wave module) drive the depth-averaged circulation module Coast for the description of the near-shore currents and sediment transport in the surf and swash zone. The module Coast is coupled with a three-dimensional bed evolution module to predict coastal bathymetry changes.

New Physical Insights and Design Formulas on Wave Overtopping at Sloping and Vertical Structures

Mean wave overtopping discharge is a key design parameter for many coastal structures, typically designed to limit overtopping discharge to below a chosen admissible value. Dutch, German, and British design guidance from the 1990s was updated using results of research projects supported by the European Commission, and subsequently unified with the publication of the European Manual for the Assessment of Wave Overtopping, or EurOtop [EurOtop. (2007). European Manual for the Assessment of Wave Overtopping, T. Pullen, et al., eds.], now used all over the world. This paper explores five technical issues that were not well covered in the unified manual. (1) For sloping structures, overtopping at low and zero freeboard conditions: new analysis brings together the conventional exponential formulas with the few reliable datasets including very low and zero freeboard. In doing so, early Dutch work from the 1970s was revisited. Weibull-type formulas are proposed, describing wave overtopping at slopes for the whole range Rc/Hm0≥0. (2) For vertical walls, the manual distinguishes overtopping responses depending upon whether wave breaking occurs, with nonbreaking and breaking conditions described by exponential and power law formulas, respectively. Here, the governing equations are manipulated in such a way as to reunify the methods, enabling direct and intuitive comparison. (3) For overtopping at vertical walls under nonimpulsive conditions, early Italian/Dutch and British formulas of the 1990s diverge significantly for higher freeboards. This paper explores why these two reliable studies arrived at two such different predictors. By reanalysis of the original datasets augmented by further data drawn from the international database on wave overtopping, a physical distinction based on the nature of the foreshore is proposed and tested. (4) The prediction method for overtopping at composite vertical structures is reworked to enable the influence of the mound to be apparent and to align with plain vertical wall formulas for smaller mounds. A new scheme is proposed that treats composite structures via a small adjustment to the new vertical wall approach proposed earlier. (5) There is vast literature on overtopping response at mildly sloping structures and substantial literature on vertical walls, but in the intervening range (approximately 1V:1.5H to 5V:1H), there is a paucity of reported tests. Recently published Belgian data have enabled the development of a continuous prediction scheme spanning mild slopes, steep slopes, and vertical structures without foreshore.

Dispersion of desalination plant brine discharge under varied hydrodynamic conditions in the south of Gran Canaria

Brine discharged directly into the sea from desalination processes, forms a very dense plume that spreads out over the sea floor following the steepest slope due to its greater density than ambient sea water. Because the large difference in density slows down brine dilution processes in ambient sea water, hypersaline plumes spread out over broad areas and affect the benthic communities in their path. The Maspalomas II desalination plant, in the south of the island of Gran Canaria (Canary Islands-Spain), discharges brine through an underwater outfall over a wide sandy bottom with a mild slope. The behavior of this brine discharge was characterized under various hydrodynamic conditions. A higher degree of hydrodynamic exposure favored dilution of the outer edges of the plume, helping to reduce the area of influence.

공간 자기상관성을 고려한 산불피해지 경계 형성과 경관특성변수들과의 관계

가장자리는 산불 피해 후 산림생태계 변화 및 회복과정에 중요한 역할을 하는 것으로 알려져 있다. 본 연구는 산불피해지의 공간 자기상관성을 고려하여 산불피해지 가장자리 형성과 경관특성변수들과의 관계 분석에 목적을 두고 수행되었다. 연구대상지로는 2000년도에 발생한 삼척 산불피해지를 선정하였으며, 대상지내 경관특성변수 측정을 위하여 산불피해지 전 지역을 포함하도록 500 <TEX>$m^2$</TEX> 격자를 생성하였다. 연구에 사용된 경관 특성 변수들로는 표고, 경사, TWI(Topographic Wetness Index), SRI(Solar Radiation Index)을 사용하였고, 연료유형변수와 토지피복 변수를 포함시켰다. 격자들은 산불피해지 경계선과 교차하는 격자는 가장자리로 그 외의 격자들은 내부지역으로 설정하였다. 공간자기 상관을 보정하기 위하여 경관 변형된 t-검정과 상관분석을 실시하였다. 분석 결과 산불피해지 경계 형성과 양의 관계를 보이는 변수는 TWI, SRI, 물, 전, 답, 개발지, 나대지이며, 음의 관계를 보이는 경관특성변수는 경사, 표고, 그리고 모든 연료 유형 변수들이었다. 특히 TWI은 r=0.437로 경계형성과 강한 양의 관계를 보였다. 따라서 산불 피해지의 경계는 산림과 이질적인 토지피복 혹은 토지이용이 존재하는 경우와 경사가 완만하고 표고는 낮으며, 토양 및 지표면의 상대습도가 높은 지형에서 형성될 가능성이 높은 것으로 나타났다. It has been known that edges of forest fire areas play significant roles in post-fire change of forest ecosystem and recovery process. The purpose of this study was to analyze the relationships between edge formation of burned forests and landscape characteristics with consideration on spatial autocorrelation. Samcheok fire site burned in 2000 was selected as the study area. Seven hundred fifty three of 500 <TEX>$m^2$</TEX> grid cells were generated for measuring landscape characteristics. This study used the topographic variables including slop, elevation, topographic wetness index, solar radiation index and proportions of fuel and land use types. In delineating landscape characteristics correlation analysis with modified t-test were performed for exploring the relationships between edge formation and landscape characteristics. The results indicated that edge formation of burned forests was positively correlated with most variables including TWI, SRI, water, paddy, developed, farm, grass, bare soil, and negatively related with elevation, slope and all fuel types. Especially TWI (r=0.437) showed a strong positive correlation with edge formation. According to the results, edge of burned forests were likely formed when proportions of heterogeneous land use types were high with mild slope and low elevation.

낙동강 하류의 퇴사저감을 위한 하폭축소방법이 홍수위변화 및 하상변동에 미치는 영향 분석

Sediment from the upstream channel has been deposited near the Nakdong River Estuary Barrage (NREB) due to the mild slope and decreased velocity. The annual mechanical dredging to ensure the flood capacity has been performed to remove the deposited sediment. However, the dredging method is not considered as an effective countermeasure due to high cost and long time to operate. Therefore, many methods for sedimentation reduction have been proposed for NREB. Especially, the channel contraction method to mitigate sedimentation problem by changing the channel geometry from 2 km to 3 km upstream of NREB has been recently suggested as an effective countermeasure. However, there is the possibility that the channel contraction method induces flood level increase compared to original condition. Therefore, it is necessary to investigate quantitatively the flood level changes in the upstream and downstream section due to the channel contraction method for NREB. In this study, water level changes by 10% channel contraction of whole width has been evaluated using the HEC-RAS model and simulated with and without channel contraction for various flood discharge. As a result, water level in the section where the channel was contracted was decreased by 0.02 m and flood level at the upstream of channel contracted was increased up to 0.015 m for the 500-year flood.

Water wave propagation equation from expanded form of Leibniz rule

The Leibniz integral rule for the first derivative with variable limits of integration is expanded for the second and the third order derivatives by using the chain rule here. Water wave propagation equation in the x-z plane containing second derivatives is depth-integrated by using the Leibniz rule. The integrated wave equation is then applied to wave transmission and reflection over an inclined step, and the computed reflection coefficients agree well with those from existing theories such as full linear equation, mild slope equation, and modified mild slope equation.

Total load transport in gravel bed and sand bed rivers case study: Chelichay watershed

Field experiments were conducted on total load transport in the Chelichay River Basin, a mountainous catchment (1,400 km2) located in north eastern of Iran, to evaluate total load formulas including four gravel bed rivers and a sand bed river (Qaresoo River). Gravel bed rivers in Chelichay River Basin can be grouped into two types; steep slope rivers with high shear values (Chehelchay River and Khormaloo River) and mild slope rivers with low shear values (Narmab River and Soosara River). Two depth integrating suspended load samplers (DH-48 and D-49), and two bed load samplers (Helley-Smith and BLSH) were used to measure total load. The performance is tested of 8 total load transport formulae including 4 macroscopic and 4 microscopic methods. A systematic and thorough analysis of 59 sets of data collected from sand bed river indicate that Yang and Engelund and Hansen reach to the better results, and from four gravel bed rivers confirmed that the methods of Karim and Kennedy and Engelund and Hansen yields the best results for steep slope rivers, and the methods of Einstein and Bijker are ranked highest in gradual slope rivers.

A breaker-zone wave energy converter

In this work we present a preliminary study on a laboratory model of a breaker zone wave energy converter (WEC). It is a heave-surge point absorber, composed by two distinct elements, a buoy and a paddle, which allows the conversion of the wave energy in near-shore region, just before waves break. The model was tested in an experimental wave flume, on a mild slope beach, with different waves breaking on the beach. We found efficiency ranging from 20 to 40 % with respect to the power of the oncoming wave.

Hybridizable discontinuous Galerkin p‐adaptivity for wave propagation problems

SUMMARYA p‐adaptive hybridizable discontinuous Galerkin method for the solution of wave problems is presented in a challenging engineering problem. Moreover, its performance is compared with a high‐order continuous Galerkin. The hybridization technique allows to reduce the coupled degrees of freedom to only those on the mesh element boundaries, whereas the particular choice of the numerical fluxes opens the path to a superconvergent postprocessed solution. This superconvergent postprocessed solution is used to construct a simple and inexpensive error estimator. The error estimator is employed to obtain solutions with the prescribed accuracy in the area (or areas) of interest and also drives a proposed iterative mesh adaptation procedure. The proposed method is applied to a nonhomogeneous scattering problem in an unbounded domain. This is a challenging problem because, on the one hand, for high frequencies, numerical difficulties are an important issue because of the loss of the ellipticity and the oscillatory behavior of the solution. And on the other hand, it is applied to real harbor agitation problems. That is, the mild slope equation in frequency domain (Helmholtz equation with nonconstant coefficients) is solved on real geometries with the corresponding perfectly matched layer to damp the diffracted waves. The performance of the method is studied on two practical examples. The adaptive hybridizable discontinuous Galerkin method exhibits better efficiency compared with a high‐order continuous Galerkin method using static condensation of the interior nodes. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Performance evaluation of multiple ground based sensors mounted on a commercial wild blueberry harvester to sense plant height, fruit yield and topographic features in real-time

Site-specific crop management can increase profitability and reduce environmental risks of wild blueberry crop having large spatial variation in soil/plant characteristics and topographic features which may affect fruit yield. An integrated automated system comprising of an ultrasonic sensor, a digital color camera, a slope sensor, a real-time kinematics GPS (RTK-GPS), custom software and ruggedized computer was developed. The system was incorporated onto a commercial wild blueberry harvester, to measure plant height, fruit yield, slope and elevation simultaneously while harvesting. Two wild blueberry fields were selected in central Nova Scotia, Canada to evaluate the performance of the system. Field boundaries, bare spots, weeds and grass patches were mapped with a RTK-GPS prior to start the experiment.Linear regression was used to calibrate the actual fruit yield with the percentage of blue pixels (R2=0.91–0.92; P<0.001; n=40) using a 0.91×0.70m quadrat at selected points from both fields. The output voltage of the ultrasonic sensor was significantly correlated with manually measured plant height (R2=0.94; P<0.001; n=13). Comprehensive surveys were conducted in both fields to measure plant height, fruit yield, slope and elevation rapidly in real-time at the same time of harvest. The maps for the measured parameters were developed in ArcGIS 10. Maps showed substantial variability in measured parameters across the fields, suggesting more fruit yield and lower plant height in low lying areas (mild slope) and vice versa. A negative relationship among fruit yield and plant height and the results of zonal statistics in ArcGIS 10 also supported the results identified by the maps. Overall, the results of calibration and mapping indicated that the developed system was an accurate, reliable and efficient to map plant height, fruit yield, slope and elevation in real-time. This information can be used to develop site-specific fertilization, based on easily measured field parameters, to optimize productivity while minimizing the environmental impacts.