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• live farthest away from the water of the three, just above the water level that the black mangrove lives in.
• sometimes have pneumatophores but they are usually less common. When pneumatophores are present they are usually less prominent than on the black.
• named “white” because of the whitish appearance of the bark.
• leaves are rounded elliptical, have two small glands at leaf base, and are more yellow-green in color.
• viviparous propagules can survive in salt water for at least 1 month.

Black Mangroves stand apart from the other species of mangroves in that they:

• live in a few inches of salt water, further inland than the Red mangroves. They can withstand higher levels of salt.
• have pneumatophores, straw-like roots that stick out vertically from the mud for gas exchange.
• named “black” because the older sections of the trunk and heartwood are blackish in color.
• leaves are narrow-elliptical and are about 2 to 4 inches long. The leaves have salt crystals formed on the top side; this is an adaption to living in high salt concentrations.
• viviparous propagules can survive in salt water for at least 4 months.

• live in deepest salt-water of the three, going from a few inches to over a foot deep.
• have large prop-roots, often times called “walking roots”, with thick lenticels for gas exchange.
• named “red” because they produce chemicals called tannins that turn the water and mud a rusty color.
• leaves are broadly-elliptical and the largest of the three (about 3 to 5 inches long).
• viviparous propagules can survive in salt water for over a year

Prior to planning a marina development a question surrounding the overall feasibility of the project should be asked.  When developing along the waterfront one of the primary questions that should be asked is “what the local, state, and federal agencies will allow for a marina and waterside development?”  Often times the environmental restrictions will dictate the type and size of marina facility in question.  Just a few of the environmental concerns that may need to be addressed are endangered species, water quality and flushing, and wave climate.

Another question that should be asked is, “what is the current market conditions and will they be able to support a marina facility”.  This is one of the key items that many waterfront developers do properly address is the demographic of the expected user, this is typically called a marina market assessment.  For example there are some locations where fishing is the primary boating activity; therefore the facility should address the types of fishing vessels (inshore or offshore) in the area.  Other locations may primarily be cruising destinations and many of the boaters will have a fairly high net worth.  This scenario may lend itself well to a megayacht marina development accommodating vessel lengths in excess of 100-ft.

The physical constraints of a marina basin are also a driving factor of a marina feasibility analysis.  If the physical constraints are not addressed properly early in the planning process the overall usability of the marina facility may have a basin that is not conducive to a profitable marina.  By understanding the market conditions and marina layout and design guidelines a marina basin can be design to be profitable and compliment the upland development.

There were days past when marinas could be used as a loss leader to sell the upland development.  With the current economic conditions the ability for a marina to turn a profit is more important than ever.  As a marina is planned, the financial and operational aspects should be as integrated into the process as the overall site constraints.   Developing a marina proforma early on in the process can help to obtain financing and demonstrate the long-term financial strength of the waterfront development.

Hans Wilson and Associates takes pride in our approach to marina development.  This process includes an integrated approach that includes market conditions, environmental factors and limitations, physical limitations, operational cohesiveness, and marina financial feasibility.

First off what is vertical datum? A vertical datum is a base measurement point (or set of points) from which all elevations are determined. Without a common datum, surveyors would calculate different elevation values for the same location. Historically, that common set of points has been the National Geodetic Vertical Datum of 1929 (NGVD29). However, as a result of advances in technology, an updated vertical datum has been created and has been officially adopted by the Federal Government as a new basis for measuring heights: The North American Vertical Datum of 1988 (NAVD88).

To develop the vertical datum, scientists measured water levels at 26 tide stations in the United States and Canada. This established the most widely known vertical datum in North America, becoming known as the Sea Level Datum of 1929, and later, known as the National Geodetic Vertical Datum of 1929 (NGVD 29). By decree, mean sea level was held fixed as a 0.00-foot elevation at each of the tide stations, and from them, 106,724 kilometers of survey leveling was run, forming the backbone for most of the elevation surveys performed.

Inherent inaccuracies were uncovered as technology grew and the demand for tighter tolerances and accuracies were required. Scientists learned that localized densities in the earth’s crust affected elevations, and improvements in global positioning satellite (GPS) systems made surveying with great accuracy over large areas economically feasible. New knowledge and technology all highlighted problems with NGVD 29.

In 1991, the North American Vertical Datum of 1988 (NAVD 88) was established by Canada, the United States and Mexico. It holds fixed a single point as the reference point from which all other elevations are measured. The District has completed its preparations to use NAVD 88 as its vertical datum, and is waiting for other agencies to complete their preparations before fully moving all operations to the new vertical datum.

What is MLW or Mean Low Water? MLW is the average of all the low water heights observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch.

A common usage is used when choosing a datum for nautical charts. For safety reasons, a mariner must be able to know the minimum depth of water that could occur at any point. For this reason, depths and tides on a nautical chart are measured relative to chart datum, which is defined to be a level below which tide rarely falls. Exactly how this is chosen depends on the tidal regime in the area being charted and on the policy of the hydrographic office producing the chart in question; a typical definition is Lowest Astronomical Tide (the lowest tide predictable from the effects of gravity), or Mean Lower Low Water (the average lowest tide of each day), although MSL is sometimes used in waters with very low tidal ranges.

Conversely, if a ship is to safely pass under a low bridge or overhead power cable, the mariner must know the minimum clearance between the masthead and the obstruction, which will occur at high tide. Consequently, bridge clearances etc. are given relative to a datum based on high tide, such as Highest Astronomical Tide or Mean High Water Springs.

High Tide

Low Tide