Morphodynamic relationships for ebb and flood delta volumes at Florida’s tidal entrances   总被引：1，自引：0，他引：1  

Mark A. Powell  Robert J. Thieke  Ashish J. Mehta 《Ocean Dynamics》2006,56(3-4):295-307

Tidal entrances constitute an important boundary condition for the coastal ocean regime. Based on data from 67 sandy entrances in Florida, morphodynamic relationships between tidal prism, entrance throat area, and ebb and flood delta volumes are revisited. The main source of sand in these deltas is the littoral zone as opposed to the river. It is found that, as a rule of thumb, the volume of a mature ebb delta is equal to one fifth of the prism at the spring range of tide. Data for the coasts of Florida taken together indicate that the volume of mature flood delta varies with one third power of the prism. The Atlantic Coast flood delta volumes by themselves do not show any correlation with the prism, presumably because entrance depths have been altered by dredging. A case study of the closure of a land barrier breach at Matanzas Inlet illustrates the application of the derived morphodynamic relationships between prism, throat area, and ebb delta volume. These relationships are useful for prediction of changes in the throat area and the ebb delta volume when morphologic changes occur over time scales consistent with the reestablishment of equilibrium.Responsible Editor: Alejandro Souza  相似文献   

A water-budget approach to restoring a sedge fen affected by diking and ditching     

Douglas A. Wilcox  Michael J. Sweat  Martha L. Carlson  Kurt P. Kowalski 《Journal of Hydrology》2006,320(3-4):501-517

A vast, ground-water-supported sedge fen in the Upper Peninsula of Michigan, USA was ditched in the early 1900 s in a failed attempt to promote agriculture. Dikes were later constructed to impound seasonal sheet surface flows for waterfowl management. The US Fish and Wildlife Service, which now manages the wetland as part of Seney National Wildlife Refuge, sought to redirect water flows from impounded C-3 Pool to reduce erosion in downstream Walsh Ditch, reduce ground-water losses into the ditch, and restore sheet flows of surface water to the peatland. A water budget was developed for C-3 Pool, which serves as the central receiving and distribution body for water in the affected wetland. Surface-water inflows and outflows were measured in associated ditches and natural creeks, ground-water flows were estimated using a network of wells and piezometers, and precipitation and evaporation/evapotranspiration components were estimated using local meteorological data. Water budgets for the 1999 springtime peak flow period and the 1999 water year were used to estimate required releases of water from C-3 Pool via outlets other than Walsh Ditch and to guide other restoration activities. Refuge managers subsequently used these results to guide restoration efforts, including construction of earthen dams in Walsh Ditch upslope from the pool to stop surface flow, installation of new water-control structures to redirect surface water to sheet flow and natural creek channels, planning seasonal releases from C-3 Pool to avoid erosion in natural channels, stopping flow in downslope Walsh Ditch to reduce erosion, and using constructed earthen dams and natural beaver dams to flood the ditch channel below C-3 Pool. Interactions between ground water and surface water are critical for maintaining ecosystem processes in many wetlands, and management actions directed at restoring either ground- or surface-water flow patterns often affect both of these components of the water budget. This approach could thus prove useful in guiding restoration efforts in many hydrologically altered and managed wetlands worldwide.  相似文献   

A radioisotope tracer investigation to determine the direction of groundwater movement adjacent to a tidal creek during spring and neap tides     

R. I. Acworth  C. E. Hughes  I. L. Turner 《Hydrogeology Journal》2007,15(2):281-296

A radioisotope tracer (⁸²Br) was injected into a sand aquifer adjacent to a tidal creek at Hat Head, New South Wales, Australia. The injection was timed to coincide with the falling limb of a spring tide in August 2001 and was repeated in July 2002 during a period of neap tides. The tracer movement was detected using gamma logging and fixed gamma detectors in a bore 0.9 m from an injection bore and in a line approximately perpendicular to the creek. Movement of the tracer was detected by comparing measured gamma activity with calibrated activities determined under laboratory conditions. Net movement of the tracer indicated approximately 0.001 m/day laterally towards the creek and 0.07 m/day vertically upward during spring tide conditions. This pattern is reversed during neap tide conditions with little net vertical movement but horizontal movement of 0.15 m/day. The measurements indicated an oscillatory motion coinciding with the tide but lagging the tide by approximately 4.5–6.5 h. The vertical flow during spring tides indicates that vertical movement of the saline interface occurs and results in mixing of different water types beneath the banks of the creek.  相似文献   

Effects of tides on a sloping shore: groundwater dynamics and propagation of the tidal wave     

A. Vandenbohede  L. Lebbe 《Hydrogeology Journal》2007,15(4):645-658

The influences of tides on a coastal environment with a sloping shore are investigated by means of field observations and groundwater flow modelling. The Belgian western coastal plain consists of a wide shore, dunes and polders where diurnal tides with large amplitude occur. The effects of tides on the groundwater flow are studied using the MOCDENS3D code. First, MOCDENS3D is validated to accurately simulate the propagation, attenuation and lag of a tidal wave in an aquifer. Then groundwater flow and influences of tides are modelled for a cross-section along the French–Belgian border. This gives an exhaustive insight into the spatial and temporal varying groundwater flow and propagation of the tidal wave in the aquifer. Simulation shows that there are two interfering flow cycles. The first is a shallow tidally fluctuating flow cycle on the shore due to the interaction of the gently sloping shore and the tidally oscillating sea level. The second is a deeper flow cycle from the dunes towards the sea. Further, it is indicated that the propagation and attenuation of the tidal wave follows a complex pattern with lateral as well as vertical components. The interaction between tides and shore topography also influences the salinity distribution.  相似文献   

A new hazard zonation methodology applied to residentially developed sea-cliffs with very low erosion rates,East Coast Bays,Auckland, New Zealand     

R. Jongens  J. Gibb  B. V. Alloway 《Natural Hazards》2007,40(1):223-244

A new hazard zonation methodology is applied to the East Coast Bays area of North Shore City, one of the most residentially developed cliffed shorelines in New Zealand. It is based on a series of geotechnical cliff profiles from three pilot study areas (George Gair Lookout, Rahopara Reserve–Kennedy Memorial Park, and Mairangi Bay–Rothesay Bay) which detail many of the variables that influence overall cliff stability. The methodology requires calculation of a Coastal Landslide Hazard Zone (CLHZ) width for each geotechnical profile and is derived by quantifying three factors: the rate of long-term sea-cliff retreat; the amount of horizontal retreat expected from either joint block fall, fault plane failure, or bedding plane failure, coupled with the amount of horizontal retreat resulting from slumping of the top weathered layer; and a safety factor. The rate of long-term sea-cliff retreat is multiplied by a hazard assessment period of 100 years, which is then added with the two other factors to derive a CLHZ width. Finally, the widths are entered into a Geographic Information System (GIS) to delineate a hazard zone. Owing to the very low rates (< 0.1 m a⁻¹) of sea-cliff retreat in the East Coast Bays area, the long-term rate of sea-cliff retreat at each profile location could not be quantified by conventional survey techniques. Instead, a Sea-cliff Vulnerability Index (SVI) was employed to quantify the long-term rate. Weighted variables considered in the SVI include the bedding dip direction, the occurrence of faults and their orientation, sea-cliff aspect, cliff-toe and cliff-face lithology, cliff-top height, and the presence of groundwater seepage. Calculated CLHZ widths along East Coast Bays range between 13 m and 34 m inland of a reference cliff-line in response to spatial variations of the sea-cliff geology and morphology. The widths reflect the estimated degree of risk over the next 100 years from coastal erosion and landslips.  相似文献   

湿地生态旅游开发的关注视角——以扎龙自然保护区为例     

张春丽  刘继斌  佟连军 《湿地科学》2007,5(2):117-123

生态旅游以其生态和环保特性成为湿地资源的一种有效的开发方式。在分析湿地生态旅游研究概况和中国湿地生态旅游发展的基础上,提出了开展湿地生态旅游的关注视角:关注湿地价值构成;关注湿地生态旅游受益群体;关注湿地生态旅游开发规模;关注湿地生态旅游管理模式。对扎龙湿地生态旅游开发进行了实证研究。  相似文献   

Suffer a Sea Change? Contrasting perspectives towards urban policy and migration in coastal Australia     

Nicole Gurran  Ed Blakely 《The Australian geographer》2007,38(1):113-131

Has the notion of ‘sea change’ and its considerable implications for non-metropolitan coastal Australia been exaggerated? In this article alternative perspectives of ‘sea change’ in Australia are reviewed, and the policy implications of each assessed. One perspective regards migration to coastal areas beyond the capital cities as incidental to continued metropolitan primacy and unlikely to affect or change Australia's overall urban or economic structure. The other considers the movement as a significant and enduring process with major environmental and socio-economic repercussions. With reference to research conducted for the National Sea Change Taskforce, the article finds partial support for both positions, leading to a more revealing understanding of ‘sea change’ in Australia. A set of policy responses, sensitive to the particular qualities of Australian coastal environments and communities, are proposed for consideration by all three tiers of government.  相似文献   

潮间带盐沼植物对海岸沉积动力过程影响的研究进展   总被引：11，自引：1，他引：11  

李华  杨世伦 《地球科学进展》2007,22(6):583-591

根据已有文献归纳出盐沼植物对水动力、悬沙运动、沉积、地貌影响研究已取得的进展，包括：①单位距离盐沼中波能的损失可为相邻光滩的数倍至数十倍；波浪传入互花米草盐沼20~30 m后，波能可全部损失；②盐沼植物可使潮流流速降低一个数量级；当植冠被淹没后，垂向流速剖面在植冠附近出现转折；③当植冠被淹没后，垂向上植冠层内的紊动强度趋于一致且明显低于植冠层以上；互花米草盐沼中的紊动强度可比相邻光滩低1~2个数量级；④盐沼植物通过2种机制影响悬沙的运动：其一是降低水体紊动，从而促进悬沙的沉降并遏制滩面沉积物再悬浮；其二是茎叶对悬沙的直接黏附。这两种机制可使盐沼中的悬沙浓度比相邻光滩低一半以上；⑤植物对细颗粒悬沙的促淤作用导致盐沼中的底床滩面沉积物细化；⑥盐沼中的垂向沉积速率可比光滩高7~8倍；盐沼中波痕和侵蚀坑等微地貌不易发育，滩面平整化；与光滩上频繁发生的冲淤交替相比，盐沼中通常只淤不冲，滩面稳定性较高；⑦植物对上述沉积动力过程的影响程度与植物的高度、密度、盖度等生态参数密切相关，因此，不同的植物种类对沉积动力过程的影响往往存在显著差异。在此基础上，展望了今后该领域研究进一步加强的几个方面。 [HT5H]关〓键〓词：[HT5K] [HT5H]中图分类号:〓〓〓文献标识码：A[HT5SS][HK]  相似文献   

浅谈宿鸭湖湿地管理与保护对策   总被引：1，自引：0，他引：1  

徐军用  刘书旺  万永程  梁志刚 《地下水》2007,29(5):124-126

宿鸭湖湿地是河南省最大的湿地自然保护区,拥有丰富的生物资源,具有巨大的环境功能和效益.因此,加强对湿地的管理与保护势在必行.根据湿地保护区的自然条件,分析保护和管理现状,从而提出了切实有效的管理对策.  相似文献   

The groundwater discharge in the Mediterranean karst coastal zones and freshwater tapping: set problems and adopted solutions. Case studies   总被引：1，自引：0，他引：1  

Borivoje Mijatović 《Environmental Geology》2007,51(5):737-742

In the karstic regions of the Mediterranean coastal zones the groundwater discharge and its outcrops—the coastal and submarine springs—represent the most typical natural phenomena of littoral karst, the economic potential of which is significant. The case studies discussed in this paper concern the problems of freshwater tapping in karst coastal zones along the Mediterranean littoral. Owing to the geological and hydrogeological approach, the set problems and adopted solutions involve two most important tasks: (1) the regulation of groundwater flow in the tapping facilities and (2) the control system of saltwater encroachment in a larger protection zone, between the coast and the site of tapping facilities.  相似文献