ESTIMATION OF TIDAL EXCURSION LENGTH ALONG THE SHATT AL-ARAB ESTUARY, SOUTHERN IRAQ

The tidal excursion length along the Shatt Al-Arab estuary was estimated based on the mathematical relation proposed by Parsa and Shahidi (2010). The field measurements of water level, bathymetry, and discharges were conducted to fulfill the objective of the study. The results revealed that the tidal excursion length is site-specific and depends on the characteristics of location which include tidal phases, bathymetry, and geometry. However, the results indicated that there are pronounced differences in tidal excursions lengths between the spring and neap tide phases in all studies stations. The spring tide coincided with the maximum tidal excursion lengths in Shatt Al-Arab estuary with 16.537, 16.187, 11.122, and 9.139 km in the estuary mouth, Faw, Siba, and Abo Flous stations respectively. While the neap tidal excursion lengths were 12.298, 9.254, and 7.269 km in Faw, Siba, and Abo Flous stations respectively.

Estuarine Exchange Flow Quantified with Isohaline Coordinates: Contrasting Long and Short Estuaries

Isohaline coordinate analysis is used to compare the exchange flow in two contrasting estuaries, the long (with respect to tidal excursion) Hudson River and the short Merrimack River, using validated numerical models. The isohaline analysis averages fluxes in salinity space rather than in physical space, yielding the isohaline exchange flow that incorporates both subtidal and tidal fluxes and precisely satisfies the Knudsen relation. The isohaline analysis can be consistently applied to both subtidally and tidally dominated estuaries. In the Hudson, the isohaline exchange flow is similar to results from the Eulerian analysis, and the conventional estuarine theory can be used to quantify the salt transport based on scaling with the baroclinic pressure gradient. In the Merrimack, the isohaline exchange flow is much larger than the Eulerian quantity, indicating the dominance of tidal salt flux. The exchange flow does not scale with the baroclinic pressure gradient but rather with tidal volume flux. This tidal exchange is driven by tidal pumping due to the jet–sink flow at the mouth constriction, leading to a linear dependence of exchange flow on tidal volume flux. Finally, a tidal conversion parameter Qin/Qprism, measuring the fraction of tidal inflow Qprism that is converted into net exchange Qin, is proposed to characterize the exchange processes among different systems. It is found that the length scale ratio between tidal excursion and salinity intrusion provides a characteristic to distinguish estuarine regimes.

A SAND BYPASSING SYSTEM USING A JET PUMP

All harbors and tidal inlets that are located in coastal areas have one characteristic in common—the need to bypass littoral materials that collect nearby. If natural harbors and tidal inlets are left unattended, bypassing will often occur naturally, but in the process, the harbor or inlet is usually rendered unfit for commercial or navigation purposes. Quite often, the inattention results in the total closure of the inlet. Therefore, at almost all harbor entrances and controlled tidal inlets, the natural bypassing must be augmented by secondary, usually mechanical, means. The customary technique for bypassing sand and maintaining harbors and inlets is the use of floating dredge equipment. This equipment is rugged, reliable, has been proved over and over, and appears to be irreplacable for many applications and locations. However, there are many locations and situations for which this floating equipment is not suitable and may, in fact, be detrimental or prohibitively costly. Waves of even moderate height, moderateto- high tidal excursion and currents, draft limitations, limited maneuvering area, and interference with normal navigation operations are examples of conditions which decrease the desirability and application of floating dredge equipment. Small volumes of material to be bypassed are an economic liability for the floating plant since mobilization and demobilization costs contribute extraordinarily to the unit cost for bypassing work.

The Exchanges of Fresh and Salt Waters in the Bay of Fundy and in Passamaquoddy Bay

The results of 385 previously published hydrographic stations in the Bay of Fundy are summarized, and the average distribution of salinity at various depths is derived from these data.The total quantity of river water accumulated within the Bay of Fundy is equivalent to the quantity introduced by the rivers during a period of about 76 days.The exchange ratios for tidal excursion segments of the Bay of Fundy range from 0.17 in the neighborhood of Cape Chignecto to 0.056 in the segment immediately south of Grand Manan. In the upper tidal reaches of the Petitcodiac River and of Minas Basin the exchange ratios are about 0.95.The estuary of the St. Croix River has been studied and calculations indicate that about 15 tides, or 8 days are required on the average to replace one day's river flow. The exchange ration in this case range from 0.905 to 0.30.From a summary of existing data in Passamaquoddy Bay it is calculated that the total accumulation of river water is equal to the quantity introduced by the rivers in a period of about 16 days.