Design & Permitting
Erosion Control Structures
Shore Protection Structures
The causes of erosion must be understood in order to proceed with design of a beach fill project. Erosion analysis provides information that can be used by the project sponsor to set project goals and objectives, and it provides the H&M Engineers with technical information to establish design criteria.
Modeling of Beach Fill
Computer Modeling of beach fill alternative designs provides H&M Engineers with a means of optimizing the design to improve the project
Sand Source Definition
The economics of beach nourishment is, to a significant extent, determined by the availability of a suitable sand source. H&M Engineers search for offshore sand sources from which sand can be delivered to the project area by hydraulic dredge. If a suitable offshore sand source can be identified, hydraulically pumping a slurry of sand and water through a pipeline is the quickest and most cost effective way to deliver large quantities of sand to a beach nourishment project.
The procedure for finding a suitable offshore sand source may vary considerably from one project to the next depending on site-specific information. A typical search begins with examination of hydrographic data to identify offshore geological features that may contain sand deposits. Likely areas may be explored by probing to identify the character of material to economically narrow the search area for more costly investigations to follow, including sub bottom seismic profiling leading to collection of undisturbed samples by vibracore, and ultimately conducting an investigation of natural resources and historic cultural resources that may be in the vicinity of potential dredging areas.
For Engineering design purposes as well as meeting agency requirements, samples from potential sand sources must be analyzed for characteristics such as the grain size distribution, mineral composition, and color, to be compared with the same characteristics of native sand on the project beach. H&M Engineers uses technical analytic procedures to determine the compatibility of the sand source material because the similarity has implications regarding the stability and success of the project, the quantity of fill that will need to be dredged, as well as environmental implications for the suitability of the beach as habitat, particularly for nesting sea turtles.
H&M staff includes Professional Engineers who have worked within the dredging industry. This unique experience, plus the firm’s experience of over 20 years in working with Dredging Contractors on the maintenance dredging of inlets, the Intracoastal Waterway, and dredging for Beach Restoration, which is often coupled with maintenance dredging of inlets, provides the expertise for H&M to plan and design dredging projects that can be completed as quickly and
efficiently as possible with consideration of specific project needs to
determine the appropriate equipment that is available within the dredging industry.
It is important to consider the tidal hydrodynamics in the design of inlet channel alignments. Giving careful consideration to how the inlet will respond to dredging can provide significant benefits. H&M has the capability, through numerical Modeling, to optimize dredging plans for long term maintenance cost reduction, and reducing potential for environmental impacts, by increasing the interval between maintenance dredging events.
Erosion Control is a term most often used in connection with the use of Erosion Control Structures. H&M Engineers has completed the design, permitting and construction of nine successful Erosion Control Projects in Florida. Erosion Control Structures differ from Shore Protection Structures in that Erosion Control structures modify the wave forces that cause erosion. Breakwaters and T-groins are the most effective Erosion Control structures because they allow coastal processes, sand transport in the littoral zone to continue and avoid impacts to adjacent beaches. H&M projects have successfully reestabli-
shed beaches for recreation, and as sea turtle nesting habitat, in areas where beach had previously disappeared as the result of earlier use of seawalls and other shore protection structures.
life. Modeling results provide some of the criteria for determining beach fill dimensions; determining how much beach compatible sand is needed and how it should be distributed along the shoreline.
Storm Protection Benefit Analysis
Shore Protection Structures stop shoreline recession for the protection of upland. Seawalls and Rock Revetments are commonly used for this purpose. H&M Engineers recommends limited use of Shore Protection Structures only in certain specific situations, because erosion control structures interact with natural coastal processes in unfavorable ways, often transferring the erosion problem to adjacent beaches. Many shorelines along which seawalls have been constructed no longer have any beach at all.
Studies have shown that development landward of shorelines with healthy wide beaches incur much less damage from storms than shorelines with narrow beaches, or no beach at all. H&M Engineers takes this into consideration in the design of Beach Nourishment Projects. H&M works with beach economists to quantify both storm protection and recreational benefits. The results of these studies are often used by project sponsors in making funding decisions, including as criteria to determine assessment levels for special Beach Management Erosion Control Taxing Districts.
Expertise with both navigation projects and hydrodynamic modeling has enabled H&M Engineers to design award-winning Marina projects in Florida. Marina design typically requires Tidal Hydrodynamic Modeling to develop a marina basin configuration that will have sufficient natural circulation that may cause water quality problems in dead-end canals or basins with restricted water flow. The navigation requirements of Marina Design not only requires dredging, but also design considerations that include criteria that determine the vessel size and fleet mix that a Marina can accommodate, based on characteristics of the waterways that provide ingress and egress to the
project site as well as consideration of proprietary rights of sovereign submerged lands which represent an essential element of regulatory approvals. H&M’s experience includes design and permitting of residential facilities as well as Marinas that include fueling facilities and ships store.
Dune restoration is often a component of beach nourishment projects because dunes enhance storm protection as well as natural beach habitat consisting of sea oats and other native beach vegetation. Dunes are therefore a practical component of technical design, and also have aesthetic value. H&M works with project sponsors in planning projects and developing criteria for determining dune requirements of nourishment projects, as well as in reconstruction of dunes to repair damage caused by storms. H&M Engineers also provide dune erosion modeling to coastal property owners, as is required by regulatory agencies for projects involving upland improvements in the zone that is regulated by Agencies for the purpose of reducing storm impacts.