Essequibo River - Geography
The Essequibo River rises in the Kamoa Mountains on the Brazilian border and flows north for over 600 miles, to enter the Atlantic Ocean through a large estuary that is filled with islands. The Essequibo River is fed by many tributaries, including the Rupununi, the Potaro, the Mazaruni, the Siparuni, the Kiyuwini, and the Cuyuni. The river's entrance is very silted up, but once over the bar, the river is navigable as far up river as Bartica, which is situated about 50 miles from the mouth. Further south the river is blocked by dangerous cataracts.
The area east of the Essequibo River, where most cultivation takes place, is protected against wave erosion by some form of sea defense, ranging from concrete seawalls to the naturally occurring cheniers. Wetland loss in the foreshore area of this coast would be considerable, and the pressure on manmade sea defense structures would increase even under a low scenario forecast for a 50-cm rise in sea level.
The Essequibo River, which is the largest river in Guyana, rises in the Acarai Mountains, in the S extremity of the country, and flows N for at least 600 miles, traversing the entire length of the country. At about 45 miles from its mouth, it is joined by the Mazaruni River and the Cuyuni River. The port of Bartica stands at the junctions of the rivers and is used by ships of limited draft.
Navigation of the river is, in general, not difficult, but during the rainy season, frequent squalls obscure the river marks and aids. Vessels generally anchor until squalls pass over. The tidal currents at the mouth attain rates of up to 3 knots at springs but decrease from 2.5 to 2 knots outside. The tidal rise at springs is about 2.7m at the mouth and about 2.4m at Bartica. The river level changes with the seasons, being highest in June and lowest in November.
The maximum difference in mean level may amount to over 0.9m. The tidal influence in the river is felt as far as Aritaka, about 17 miles above Bartica. At the entrance to Ship Channel, the main entrance to the river, is a bar with a least depth in the fairway of 2.1m. A ship that can cross the bar can ascend the river to Bartica and the Mazaruni River to D'Urban Island, about 50 miles from the sea and 1 mile below the first rapids.
The estuary of the river is encumbered by a number of islands from which shoals and sand banks extend from the outer islands to the 5m curve, which lies as far as 17 miles seaward. Frequent changes in depths in the river and estuary are liable to occur owing to the shifting nature of the banks.
The sand banks on both sides of Ship Channel are fairly steep-to and must be approached with caution. Sand banks, steep-to on their N sides, are characteristic of that part of the river between Mamarikuru Bank, 10 miles below Bartica, and Lamun Island, just above Bartica. These steep-to edges are almost at right angles to the direction of the tidal currents. Tide rips occur during ebb tide at these steep-to edges.
The main entrance of the river is through Ship Channel, which is entered between Leguan Island and the mainland. The river fairway is marked in places by navigational aids which are changed with the shifting shoals and require local knowledge to clear them. The twin chimneys, located about 5 miles SSE of the NE end of Leguan Island, are good landmarks. West Channel and Middle Channel, both N of Ship Channel, also lead into the Essequibo River. However, the use of West Channel and Middle Channel has been discontinued.
The coasts of Guyana, Suriname and French Guiana are mostly low and forested with mangrove and tropical vegetation. The extensive coastal banks and shoals fronting much of these coasts require that ships along these coasts be well offshore outside the sight of land, except when approaching a port. Much of the charted hydrography is from old and imperfect surveys. This fact, coupled with the estuarial nature of the river ports and continual changing of the bar depths, requires the utmost prudence in navigation. Numerous wrecks exist along the coast and off the entrances to the rivers. Due to the shallowness of the water, almost all are dangerous to navigation.
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