Barrier‐spit geomorphology and inlet dynamics in absence of tides: evolution of the North Pond system,eastern Lake Ontario,New York State

Barrier systems have received much attention along microtidal oceanic coastlines, where countless studies discuss their evolution in response to Holocene sea‐level rise, storm influence, and anthropogenic impacts. Lacustrine barrier evolution is not as well investigated and little is known about how lake‐specific hydrodynamic processes shape barrier morphology. This study evaluates the evolution of a highly dynamic barrier section along eastern Lake Ontario in the context of varying water levels and winter‐ice covers. Paleoshoreline reconstructions and volumetric analyses of nearshore sedimentation indicate the central portion of the studied North Pond barrier has been breached many times in different locations throughout the last century. Ground‐penetrating radar (GPR) data corroborate mapped locations of former inlets, bound at the surface by recurved spit and dune ridges. Subsurface structural controls on inlet position are inferred from a spatial correlation with buried incised fluvial channels, formed during a Holocene lake‐level lowstand. While subsurface controls caused two separate historical inlets to remain stationary while open, an episode of rapid inlet migration elsewhere along the barrier was facilitated by the prevailing direction of coastal currents and high lake levels, which favored overwash and rapid longshore sediment mobility across a low‐gradient barrier section. Additionally, the sudden closing of an inlet after many decades of operation coincidental with the opening of another suggestively occurred alongside unusually high lake levels. These correlations suggest the degree of coastal inundation, predominantly a function of fluctuating lake levels and antecedent topography, represent strong controls on overall barrier geomorphology over decadal timescales. Copyright © 2016 John Wiley & Sons, Ltd.     

Multi-decadal coastal change in New Zealand: Evidence, mechanisms and implications

Abstract:   Coastal research and monitoring on New Zealand beaches have typically examined seasonal and event-driven (storms) changes in the coast. However, historical records are now of sufficient length to indicate that change occurs at longer timescales. This paper presents examples of multi-decadal change at three case-study locations around New Zealand. Results show that morphological adjustment of the coast occurs at multi-decadal scales and is much larger than short-term dynamics. Physical mechanisms driving changes are ill defined but may be associated with El Niños and La Niña episodes which modulate waves and sea level, as well as changes in sediment supply.     

Facies architecture and depositional processes of the Holocene–Recent accretionary forced regressive Skagen spit system, Denmark

Spit systems are seldom recognized in the pre‐Quaternary sedimentary record compared to their common occurrence along present‐day coasts and in Quaternary successions. This lack of recognition may partly be due to the lack of widely accepted depositional models describing the facies characteristics of spit systems and their subaqueous platforms in particular. The Skagen spit system is a large active system that began to form 7150 yr bp and from 5500 bp to Recent times it has prograded 4 m year^?1 and accumulated 3·5 × 10⁹ m³ of sand. The spit system provides a unique opportunity for establishing a well‐constrained depositional model because uplift and erosion have made large windows into the preserved facies, while active spit‐forming processes can be examined at the young prograding end of the same system. The depositional model presented here thus builds on excellent outcrops, surface morphology, a well‐defined palaeogeography and detailed C¹⁴ age control supplemented with observations from continuous well cores and profiles obtained by ground‐penetrating radar and transient electromagnetic surveys. The factors that have governed the development of the spit system, such as relative sea‐level change, wave and current climate, tidal range, sediment transport and depositional rates are also well‐understood. The sedimentary facies of the spit system are grouped into four principal units consisting from below of thick storm sand beds, dune and bar‐trough deposits, beach deposits and peat beds. These four units form a coarsening and shallowing upward sand‐dominated succession, up to 32 m thick, which overlies offshore silt with a transition zone and is topped by a diastem overlain by young aeolian dune sand. The sedimentary structures and depositional processes are described in detail and integrated into a depositional model, which is compared to other spit systems and linear shoreface models.     

Application of wave transformation models for estimation of morphological changes at Vellar estuary,southeast coast of India

Assessment of the wave climate at near coast is vital for estimation of morphological changes, such as growth of sand spit and associated siltation of tidal inlets. Vellar (bar-built) estuary is one of the prominent estuaries along the southeast coast of India, located at 11°30′N and 79°46′E, less studied in terms of its morphological features. The inlet of Vellar is exposed to high energetic waves, inducing large sediment transport rates and shoreline changes. Local wave characteristics are not accurately defined and the available wave information at near coast is limited (point based observations). In the present study, three decoupled numerical models are employed to derive the monthly nearshore wave climate at Vellar by transforming waves from deep water to nearshore. These models are independently validated with buoy observations in deep water and wave gauge data at nearshore. Based on the nearshore wave data, littoral drift along the coast was estimated and compared with the spit growth at Vellar inlet. The estimated average littoral drift along this coast from February to October is 1.93 × 10⁶ m³ toward north and from November to January it is 1.52 × 10⁶ m³ toward south, resulting in a net northerly drift. Results indicated that increase in the wave energy during the period of July to September is responsible for the maximum growth of the sand spit observed in the field.     

Sand-spit erosion following interruption of longshore sediment transport: Shamrock Island, Texas

 Shamrock Island, located in Corpus Christi Bay, Texas, is a former sand spit that was detached from Mustang Island by navigation channels constructed in the early 1950s. The navigation channels effectively eliminated longshore sediment transport to the island, resulting in severe and ongoing erosion of the island's north shore. This study documents long-term shoreline change, based on analysis of aerial photographs from 1938, 1948, 1950, 1952, 1956, 1967, 1975, 1979, 1985, 1990, and 1995. Shamrock Island grew steadily to the south prior to 1956, while the north shore of the island was relatively stable. After 1956, the north shore eroded rapidly, while the south shore continued to grow, probably because sand eroded from the north was redistributed to the south. By 1995, up to 156 m of retreat had occurred on the north shore. The island was recently acquired by the Nature Conservancy of Texas for use as a nature preserve. Erosion now threatens to breach the island, which may result in degradation of an interior lagoon and loss of valuable wildlife habitats. Therefore, in addition to documenting long-term erosion following interruption of longshore sediment transport, this study also illustrates how human modification of the coastal zone can have important and unforseen ramifications affecting future shoreline uses for many decades. Received: 6 October 1997 · Accepted: 3 February 1998     

Coastline sand waves on a low-energy beach at “El Puntal” spit, Spain

Coastline sand waves have been observed at “El Puntal” spit, located on the north coast of Spain. The spit has been monitored by an Argus video system since 2003 and the formation and destruction of sand waves has been observed. Coastline data from the video images are analyzed by means of principal components analysis, obtaining a mean sand wave length of 125–150 m and a maximum amplitude of ≈ 15 m. It is also observed that sand waves reach their maximum amplitude at about 15 days. No propagation of these sand waves is noticed during the approximately two-month-long events analyzed. Sand wave formation and evolution are examined in relation with the prevailing local wave conditions during that period. Incident waves at the west end of the spit approach from the east–northeast, with a very high angle with respect to the shoreline. Field observations suggest that sand waves may result from an instability in alongshore sediment transport caused by moderate-energy waves with a high-angle incidence.     

雷州半岛灯楼角沙岬的形成

沙岬(沙嘴)是一种海岸动力地貌类型。通过区域地貌背景、海底地貌-浅地层、海洋动力条件、相关的海岸沙坝和现代海滩的分析,认为灯楼角沙岬是来自琼州海峡的东向波浪和来自北部湾的西向波浪两种相向波浪动力平衡、灯楼角东沿岸存在逆时针环流和灯楼角西沿岸存在顺时针环流两者于此辐合,并把带来的砂子沉积下来的结果。     

An examination of the use of scales and fin rays for age determination of brown trout (salmo trutta L.)

Scales and fin rays from brown trout (Salmo trutta L.) of known age were examined. Only 6 out of 29 scales were read correctly by 2 operators. The commonest fault was to read an extra year into the first year's growth. Fin ray sections proved much easier to read than the scales. The author correctly read all of a sample of 22 fin ray sections.     

Total sediment budget of a transgressive barrier-spit,Skallingen, SW Denmark: A review

Average sea-level rise in the northern part of the Danish Wadden Sea has been 1.3 mm a^?1 during the last 100 years but during the last 25 years a rise of 4.2 mm a^?1 was observed. Concurrent with the recent sea-level rise the Skallingen barrier spit has migrated landward by 3–5 m a^?1. Long term sediment budgets for each of the morphological units involved in the migration are reviewed (e.g. onshore in the shore face +90.000 m³ a^?1, longshore -641.000 m³ a^?1, foredunes +65,000 m³ a^?1, overwash fan including shorenormal dunes +11,000 m³ a^?1, spit terminus -96,000 m³ a^?1, tidal flat + 10,000 m³ a^?1 and backbarrier salt marsh +33,000 m³ a^?1) and used to establish the relative importance of sediment transport processes involved in barrier migration. Strong interannual variations exist in the long term budget making evaluation of barrier behaviour based on short term measurements doubtful. In a cross shore sense the barrier spit is accreting in spite of the sea level rise. This is specially pronounced at an active overwash fan. However, due to substantial sediment losses to longshore transport the barrier, gets narrower and shorter during its transgressive behaviour. This may indicate that preservation of barriers in the geological record during rapid sea level rise is promoted when sediment loss to longshore transport is insignificant.     

Stability of a sand spit due to dredging in an adjacent creek

The Jatadharmohan creek lies between Mahanadi and Devi Rivers along the Orissa coast and it is separated from the sea by an elongated sand spit. It was proposed to mine a volume of 15×10⁶ m³ of sand from the creek for land filling, but maintaining the spit intact. For this, the stability of sand spit is studied with different criteria. The results confirm that the creek mouth is a near permanent zone of deposition. The model results obtained for various depth scenarios show that the magnitude of currents would increase considerably when depth is increased by 7.0 m and marginally for further increase in depth by 10.0 m. Accordingly, a dredging scheme has to be designed without affecting the spit stability. Considering the existing hydrodynamics in the creek system, it is recommended that a bed slope of 1:6 (9.5°) be maintained during dredging, which is much less than 13.75°—the evaluated critical slope at the site when seepage flow is parallel to the bed slope. It is observed during monitoring that the creek is very productive, and the sand spit is totally intact.