Mean Low Water Research Articles

TIDES IN HOOGHLY RIVER

Summary The Hooghly is a tidal river and Calcutta one of the most important ports of India is situated on it. The tidal effect stretches to over 175 miles length up to Nabadwip where two nonperennial rivers Bhagirathi and Jalangi, both taking off at different sites from the Gangesmeet and discharge their rain water (freshets) into the Hoogly all through the summer months. Other rivers join it also downstream. Annual tide tables are published for three places on the river viz Sagar, Diamond Harbour and Garden Reach. In this paper lunitidal intervals, durations of rise and fall, mean high water, mean low water, mean tide level and mean sea level planes and mean ranges have been shown to go through periodic seasonal changes. It has been shown that different tidal planes have changed differently in the intrior of the river indicating changes in tidal regimes and in the river bed. Whereas variations in yearly sea levels since 1882 have not been appreciable at Sagar, these at Garden Reach have changed considerable at indicating sometimes an improvement in the channel, other times worsening of the channel. Four 19 yearly cycles of mean sea-level at Garden Reach have been analysed to give phaselags different from Zero and large variations in amplitudes. To carry this study further one period of 19 years each for Sagar, Madras and Vishakhapatnam on East Coast and 4 periods each for Bombay and Aden in the Arabian Sea have also been analysed to see the possibility of nodal variations being constant in amplitude and phase over large areas of the ocean. 19-yearly cycles in the differences between MTL & MSL have been examined for Bombay, Madras and Garden Reach. The effects of freshets on various planes have been analysed and the curves of annual freshets and MTLs at Garden Reach are found to run closely parallel. The variations in yearly high water and law water planes above MTLs of the corresponding years after corrections for the longitude of the moons' node have been found to be inappreciable. Theoretical extreme high water and low water planes have been found to be more extreme than actually recorded planes which are very near M.H.W.S. and M.L.W.S. planes indicating there are no predominant effects of winds and storms on the tides in the river. The mean ranges at Garden Reach have been found to be steadily increasing. Theoretical effects of increase in range and lowering of MSL on MHW and MLW plane has been found to agree with actual values. Monthly average temperatures and salinities show distinct annual cycles. High temperatures occur at the same times as low salinities and high mean sea levels. Vertical density structure may be responsible for a large part of annual variation in the sea level at Sagar which is a region of particular interest on account of opposite influences of seasonal monsoons, drainage of rivers and oceanic currents. Seasonal variations in average monthly pressure have been related to variations in mean sea levels and it is found that as the pressures decrease, the height of MSL increases. Tide in Hooghly has been found to be progressive type of wave. Rates of travel of tidal streams outside Sagar and rates of streams in the river have been given also, stating the effects of freshets on tidal streams. Bores in Hooghly have been examined. Shapes of tidal curves and profile of the bore at Garden Reach have been drawn. Rates of propagation of the bore from Doodsons' formulae have been compared with actual values and a remarkable agreement has been found. The rise of tide in 10 minutes and 30 minutes which is the time taken for the steep rise to disappear has been correlated with range of tide and a useful table has been included. Tides in Hooghly are predicted by applying harmonic shallow water corrections to open sea primary predictions at Sagar. As the freshets are unpredictable an approximate relationship has been worked out between the departures of actual freshets from num freshets of the years of analyses and departures of actual from predicted tides. From a knowledge of actual freshets the predictions can be corrected almost, daily. A large number of tables and only the essential graphs have been included to illustrate the contents.

STUDIES OF THE NIANTIC RIVER, CONNECTICUT WITH SPECIAL REFERENCE TO THE BAY SCALLOP, AEQUIPECTEN IRRADIANS1

The Niantic River is a shallow estuary with a tidal prism equal to half the mean low water volume of the basin, and with a twelve‐hour freshwater inflow of less than 3% of the tidal prism. The tidal waters mix offshore with the waters of eastern Long Island Sound, rich in plankton and nutrients. The estuary functions as an ecological concentrating system as the dense and varied populations of grazers consuming the food of these tidal waters benefit from the resources of offshore mixing in addition to the production endemic to the estuary.The disappearance of the eelgrass, Zostera marina, with the epidemic of the early 1930's permitted better circulation near the river bottom. Apparently this was advantageous to the bay scallop, which thereafter became the predominant sessile grazer with a production calculated at 2.2g C/m2/yr. Anchorage previously offered by eelgrass for the early setting stages of scallops was subsequently available through the abundance of small branching algae.The brief life history of a bay scallop is outlined on its shell as the surface laid down in each successive year appears rougher or more “weathered” than that formed the year before. By following this differentiation of shell surface, annual rings were determined with more certainty than in earlier studies. Though the time of year when the differentiation of shell surface commences may vary with populations and even with year classes, it is probably due to a common cause, seasonal change in growth rate being most likely. The life history interpreted from shells from Indian middens was essentially the same as observed for living scallops.The scallops of the Niantic River spawn from mid‐June through July. The young of a given year reach maturity and are the chief brood stock of the succeeding spawning season. Mortality rates for all sizes are high during all seasons and few individuals survive to the time of second spawning.The estuaries in which the bay scallop occurs have the following hydrographic features: the ratio of tidal volume to river flow is high, thus the salinity remains high; the basin is relatively shallow, with a resulting high ratio of tidal volume to the volume at low water; the circulation is such as to retain the planktonic scallop larvae in sufficient numbers for reseeding and to provide an adequate supply of planktonic food, perhaps in part supplied by offshore waters.

SAND TRANSFER, BEACH CONTROL, AND INLET IMPROVEMENTS, FIRE ISLAND INLET TO JONES BEACH, NEW YORK.

Long Island, New York (Figure 1) extends for about 120 miles in a general east-west direction off the southern portions of the States of New York and Connecticut, from which it is separated by Long Island Sound. The western end of the island contains the Counties of Brooklyn and Queens which are part of New York City. To the east are the Counties of Nassau and Suffolk. The surface geology of Long Island is mostly of glacial origin. That portion of the south shore of Long Island with which this paper is concerned (Figure 2) consists of outwash plains of sand and gravel fringed by barrier beaches from 600 feet to 3,500 feet in width. They rise to about 15 feet above mean sea level, and in their natural condition are more or less protected by sand dunes which may reach an elevation of from 25 feet to 30 feet. The sand along the foreshore is predominantly quartz, averaging about 0.4 mm. at mid-tide level, and becoming somewhat finer offshore. The foreshore slope of the beaches averages about 1 on 10 above the mean low water line and about 1 on 30 immediately offshore. Several hundred feet offshore the slope flattens to about 1 on 250.

Sand By-Passing Plant at Lake Worth Inlet, Florida

Inlet provides access to Port of Palm Beach; channel is 300 ft wide between rubble stone entrance jetties 900 ft apart, concrete capped to elevation 7 ft above mean low water; littoral drift and impoundment effects; replenishment of beaches; 23 by 40 ft monolithic concrete pumphouse is equipped with 12 in. pump of 4000 gpm capacity, handling 15% solids suction line, discharge line and flushing equipment.

SEASONAL GONADAL CHANGES OF ADULT CLAMS, VENUS MERCENARIA (L.)

The literature on Pelecypoda mollusks contains but few accounts of systematic studies of the changes occurring in the gonads of an animal throughout the entire year. This phase of investigation of sexual phenomena in mollusks, though neglected so far, is, however, of considerable importance and interest because, if properly carried out, it could assist greatly in the understanding of the phenomena of change of sex in some forms or add to the knowledge of the alternation of sexual phases in others. Amemiya (1929) reported a very interesting case of sex change in the Japanese oyster, 0. gigas, which was previously considered dioecious. His method consisted of making a hole in the shell of an oyster and removing through it a small piece of gonad for determination of sex. Following this the oysters were placed in cages and returned to the water for a period of one year, at the end of which they were re-examined. Meanwhile, no samples were taken for histological studies to determine what cellular changes precede the reversal of sex. Nelson (1928) gave a more or less detailed description of changes occurring in the gonads of the adult 0. virginica from April until June, but did not continue his studies through the post-spawning time and season of hibernation. In other studies dealing with sexual phenomena of the genus Ostrea, a systematic description of changes occurring in the gonads of adult animals throughout the year is also lacking. This paper deals with the changes occurring in the gonads of adult clams (Venus mercenaria) at different seasons of the annual cycle. The animals were studied for three successive years. Samples for this study were collected at bi-weekly intervals from the clam beds located near Charles Island, Long Island Sound. The depth of the water over the beds was 8-12 feet at mean low water. Since the calendar's new year, occurring in the middle of winter, coincides with the prolonged period of the animal's inactivity, it is thought convenient in this study to consider the beginning of a new year from the ecological point of view, i.e., after the completion of

A Study of the Community Relationships of the Sea Mussel, Mytilus Edulis L.

EcologyVolume 16, Issue 2 p. 234-243 Article A Study of the Community Relationships of the Sea Mussel, Mytilus Edulis L. Curtis L. Newcombe, Curtis L. NewcombeSearch for more papers by this author Curtis L. Newcombe, Curtis L. NewcombeSearch for more papers by this author First published: 01 April 1935 https://doi.org/10.2307/1932430Citations: 17AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume16, Issue2April 1935Pages 234-243 RelatedInformation

The Nature of the Intertidal Zonation of Plants and Animals

1. Church Reef, in Wembury Bay, near Plymouth, was selected for a survey of common intertidal plants and animals.2. Four traverses were accurately levelled relative to Ordnance Datum, and their floras and faunas examined.3. The relation between predicted tide levels and probable actual levels is discussed, and the importance of the “splash zone” is stressed.4. As an outcome of 2 and 3, it appears that on Church Reef the most critical levels on the shore, for the species examined, are: (a) between Mean and Extreme Low Water Springs; (b) between Mean Low Water Neaps and Springs; (c) at Extreme (Lowest) High Water Neaps. The least critical level is Mean Low Water Neaps.5. Two special problems are presented by the upper limits of Littorina saxatilis and L. neritoides, and by the frontiers between Ascophyllum and Fucus spiralis and between F. spiralis and Pelvetia, where the algæ do not overlap.6. The work of previous authors is discussed for comparison with the present paper.7. An important difference is suggested between the nature of the zonation of sedentary animals and plants on the one hand, and that of animals capable of locomotion on the other hand.

STRUCTURE AND DEVELOPMENT OF ZONARIA FARLOWII

Morphological studies in the Dictyotaceae have been confined largely to Dictyota, whose life history has become well known through the work of a number of investigators. Padina has received some critical attention, but the dozen or more other genera have been largely neglected. One of these, Zonaria, is of particular interest because of the peculiarity of certain features of its morphology. For the most part, Zonaria is a tropical genus, its various species being widely distributed. The present investigation is based on Z. Farlowii S. and G., which grows abundantly along the coast of southern California in the vicinity of Laguna Beach. Nearly all of the material used in the present study was collected near Abalone Point, about two miles northwest of the village. A few plants were collected along the coast about midway between San Pedro and Redondo Beach, but the species is much less abundant there. Other Dictyotaceae found at Laguna Beach include Dictyota flabellata (Collins) S. and G., D. Binghamiae J. Ag., and Neurocarpus zonarioides (Farlow) Howe, forms which are also common farther north. Setchell and Gardner (io) give the distribution of Zonaria Farlowii as Santa Barbara to San Diego. In the region where the material for the present study was collected, Zonaria grows attached to rocks in tidepools. It grows where, at the time of the lowest spring tides, it will still be covered with water. Lack of facilities for gathering plants in deep water or at night restricted collecting to times when the lowest tides came during the hours of daylight. The datum used by the U. S. Coast and Geodetic Survey in reckoning tidal heights along the California coast is mean lower low water (ii). It was found that the best collecting could be done when the height of the water was at or below this level, and that little or no material could be obtained when the water was more than 15 cm. above it. During the months of June, July, August, and September the lowest tides occur at night, and consequently daytime collecting in shallow water was further limited to the period of the year from October to May, inclusive, the most favorable spring tides occurring from October to February, the most favorable neap tides during March, April, and May. Since the facilities of a marine laboratory were not available, daily observations could not be made, or culture work carried on under natural conditions. The location of the writer's headquarters sixty miles from Laguna Beach, 23 239