Vegetation succession of low estuarine marshes is affected by distance to navigation channel and changes in water level

For an offshore LNG project situated in the estuary of the Rio de la Plata nearby Montevideo, Uruguay, it was required to verify the deterministic design of the protective rubble mound breakwater and the jetty infrastructure with a level three probabilistic design. Therefore, in first instance extreme site conditions were required both in front of and behind the breakwater. To obtain these conditions, the first step is to extrapolate the offshore variables in order to translate them to the breakwater location. All the possible combinations of extreme wind, water level and waves are quantified with a probability of occurrence. A combination of univariate extreme value distributions, copula’s and regression is used to describe the multivariate statistical behaviour of the offshore variables. The main variable is the wind velocity, as in the area of concern extreme wave conditions are wind driven. The secondary variable is water level. Wind velocity and water levels are only correlated for some wind directions. For these directions, wind velocity and water level extreme value distributions are linked through a multivariate Gumbel Copula. The wave height at the model boundaries was taken into account by a regression function with the extreme wind velocity at the offshore location and the wave period by a regression function with the wave height. This way 1515 synthetic events were selected and simulated with the spectral wave model SWAN, each of which a frequency of occurrence is calculated for. However, due to refraction and diffraction effects of the approach channel (in the area of concern water depths are limited to about 7 m and the navigation channel has a depth of about 14 m), the port basin and the breakwater itself, the spectral wave model SWAN is not sufficient to accurately calculate the local wave conditions in the entire area of interest. Therefore a non-linear Boussinesq wave model (i.e. Mike 21 BW) was set up in addition, using input from the spectral model at the boundary and including the navigation channel of more than 12 km long. Combining both models, significant wave heights are obtained on both the seaward side and the leeside of the breakwater with corresponding frequencies of occurrence. This approach allows the determination of conditional return periods and generates the site conditions required for a probabilistic level three design of the breakwater and the jetty infrastructure taking for example the joint probabilities between waves and water levels fully into account as needed for overtopping or failure calculations.

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Factors influencing the number of breeding water birds in Lake Engure, Latvia

Proceedings of the Latvian Academy of Sciences Section B Natural Exact and Applied Sciences ◽

10.2478/v10046-011-0028-y ◽

2011 ◽

Vol 65 (5-6) ◽

pp. 127-137

Author(s):

Jānis Vīksne ◽

Māra Janaus ◽

Aivars Mednis

Keyword(s):

Water Level ◽

Natura 2000 ◽

Vegetation Succession ◽

Natural Food ◽

Lake Area ◽

Nature Protection ◽

Factors Influencing ◽

Water Birds ◽

Indirect Impacts ◽

The Impact

Factors influencing the number of breeding water birds in Lake Engure, Latvia Lake Engure has attracted great interest since the middle of the 19th century when the water level of the lake was lowered by construction of a canal. The lake area decreased from 90 km2to about 45 km2, and favourable conditions were created for development of emergent vegetation (presently covers 58.6% of area). A nature protection regime was established in 1957. The lake was included in the Important Bird Area list in 1994, in the Ramsar lists in 1995, and as part of the Natura 2000 network in 2004. The present paper deals mostly with data collected by the Laboratory of Ornithology, Institute of Biology, in the period 1948-2011. Direct and indirect impacts of climate, human activities, water level, vegetation succession, anthropogenic and natural food and predation on water birds (coot, waders, ducks, larids and grebes), as well as relationships between these water bird groups, were demonstrated. The impact of vegetation succession via overgrowing of meadows with reed and bushes, merging of the mosaic of small stands of emergents into huge reed dominated massives (thus reducing areas of habitats suitable for water birds) is described. The relation of Black-headed Gull population size with availability/unavailability of anthropogenic food and the associated changes in breeding duck numbers, as well as predation structure are discussed.

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Long-Term Study of the Relationship between Precipitation and Aquatic Vegetation Succession in East Taihu Lake, China

Scientifica ◽

10.1155/2017/6345138 ◽

2017 ◽

Vol 2017 ◽

pp. 1-8 ◽

Cited By ~ 5

Author(s):

Yehui Zhang ◽

Na Yang ◽

Jiawei Xu ◽

Yixing Yin

Keyword(s):

Water Level ◽

Aquatic Plants ◽

Aquatic Vegetation ◽

Taihu Lake ◽

Vegetation Succession ◽

Annual Rainfall ◽

Dry Period ◽

Long Term Study ◽

The Relationship

Based on long-term rainfall measurements (1956–2012), water level records (1956–2006), and aquatic plants field survey data (1960–2014), the relationship between precipitation and aquatic vegetation succession in east Taihu Lake, China, is studied. Neither abrupt changes nor any trends were found in the annual rainfall series in Taihu Lake during the studied period (1956–2012). However, for seasonal variations, statistically significant decreases are found in spring and autumn, while the rainfall in winter exhibits statistically significant increase. No significant trend was obtained in summer. A “dry” period was detected in our studied period (1963/1964~1978/1979). Total annual rainfall was significantly positively correlated to the number of rain-days (r=0.59) and the water level (r=0.84). Our results indicate that the variations of rainfall and water level may have an impact on the aquatic plants in Taihu Lake. The dry period may be not suitable for the growth of the aquatic plants. All aquatic plants in Taihu Lake were dramatically reduced in the dry period, especially for submerged macrophytes and floating-leaf macrophytes. Our results may be helpful for the aquatic restoration in the future.

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Underkeel Clearance Reliability Model for Dredged Navigation Channels

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/2611-05 ◽

2017 ◽

Vol 2611 (1) ◽

pp. 41-49 ◽

Cited By ~ 3

Author(s):

Brandan M. Scully ◽

Kenneth Ned Mitchell

Keyword(s):

South Carolina ◽

Water Level ◽

Resource Constraints ◽

Potential Method ◽

Maintenance Cost ◽

Automatic Identification ◽

Identification System ◽

Army Corps ◽

Navigation Channel ◽

Channel Maintenance

This paper presents a reliability measure for selecting marine navigation channel maintenance depth. Resource constraints have resulted in dredging requirements outpacing the funds available to the U.S. Army Corps of Engineers to perform navigation channel maintenance dredging, but navigation managers lack a method to objectively select maintenance depth alternatives to authorized project depths. The reliability of a navigation channel can be determined as the probability that a vessel's net underkeel clearance is greater than or equal to 0. Net underkeel clearance was hindcast from underkeel clearance contributors that include sailing draft, water level, bathymetric elevation, vessel squat, and wave response. This method was tested in Charleston Harbor, South Carolina, with an authorized depth of 45 ft (13.7 m). The harbor includes two-way container, tanker, roll on–roll off, and passenger traffic with maximum drafts exceeding design depth. Vessel squat in transit is calculated on the basis of vessel speed, obtained from Automatic Identification System (AIS) data and a representative block coefficient based on vessel size and type. This study used archival AIS data, bathymetric surveys, observed water level elevations, and information collected by vessel pilots to calculate net underkeel clearance of vessel transits through each dredged location within the harbor in 2011. It was determined that channel reliability ranged from 98.7% to 100%. Channels with 100% reliability had minimum net underkeel clearance between 1.0 ft (0.3 m) and 8.3 ft (2.5 m). The approach provides a potential method to select maintenance depth alternatives to authorized channel depths that may result in maintenance cost savings that arise from avoided dredging and associated material management costs.

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Stable cross-sectional dimensions for navigation channel in the estuary of Sangatta River, Indonesia

E3S Web of Conferences ◽

10.1051/e3sconf/202132505003 ◽

2021 ◽

Vol 325 ◽

pp. 05003

Author(s):

Tommy Sutarto

Keyword(s):

Water Level ◽

Cross Sections ◽

Critical Condition ◽

River Flow ◽

Sea Water ◽

River Estuary ◽

Hydraulic Analysis ◽

Cross Sectional ◽

Depth Profiles ◽

Navigation Channel

The objectives of this study are: 1) to capture the existing condition of the river channel in Sangatta River estuary, including the bathymetry of the river bed, and the cross-sectional dimensions of the river, 2) to design a stable navigation channel in Sangatta River estuary that allows less maintenance dredging and improves navigability of the channel during a critical condition when the water level is at the lowest, and 3) to test the effectiveness of the stable cross section in term of the availability of navigable depth. This research is divided into five stages, namely: 1) preparatory stage and preliminary survey, 2) main surveys, 3) hydrological and hydraulic analysis, 4) waterway design, and 5) dredging plan. The hydraulic analysis also includes determining the water level and depth profiles before and after dredging. HEC-RAS software is used to simulate, for each month, the water level and depth profiles in the channel at a critical condition when the sea water level is at low water spring (LWS) coincides with the river flow of 50% probability of occurrence, Q50. A stable channel for Sangatta River estuary is characterized with a bed slope, S = 0.00015, a flow depth, D = 3.6 m, a bed width, b = 76.3 m and a sidewall slope, m = 1.5. The simulation results show that the stable cross sections of the river provide sufficient water depth for navigation, even during the critical condition.

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