Dredging Terms and Explanations

• Hydraulic Dredging
• Dredge Configurations
• Hydrographic Survey
• Material Classification
• Angle of Repose
• Side Slopes
• Over Dredging
• Spoil Areas

1. Dredging (hydraulic): is the removal of sand, sediments, silts, fines and sludge from the bottom of ponds, lakes, rivers or any other contained waterborne environment. The material is removed via the dredge and pumped to a material disposal site through pipelines.
2. Dredge configurations: hydraulic dredges come in several different types and varying sizes. The size is designated by the pump discharge diameter and the configuration is determined by how it operates. Bull dredging operates 8” cutter suction and auger type dredges. Our equipment moves throughout the dredging area either via a cable and harness system or independently with a travel spud system.
   1. Bull Dredging asses each project site and utilizes the type dredge that is most suited to complete the project in a cost effective, efficient and timely manner.
3. Hydrographic survey: defined as a valid and reliable means to measure and record the bottom depth of a specific area in a waterborne environment. Several differing survey methods are employed and accepted within the industry. They range from electronic depth sounding instruments to sounding poles “measured in feet and tenths” to sounding chains. Positioning methods also vary and range from electronic global positioning systems “GPS ” to setting up and using a base line and range grid, within the dredge area.
   1. Pre, interim and post hydrographic surveys determine the actual depth of bottom and provide figures to quantify the number of cubic (Y3) removed during operations. Interim surveys also provide the dredge operator valuable information relative to vertical and horizontal excavation quality control.
   2. Depending on the size of the area to be surveyed, the type and complexity of the equipment desired and the funding available, you may choose between hiring an independent hydrographic survey company or doing the surveys internally in conjunction with our operations. Which ever survey method is chosen, it is best to stay consistent throughout the project. Bull Dredging is well versed in hydrographic survey methodology and can discuss your options with you.
   3. For validity, the closer to the date of actual dredge commencement that a pre-hydrographic survey is to run, the better. Bottom conditions can and do change frequently depending on the type waterborne environment present.
4. Material Classification: Dredge materials are classified by the composition of their makeup. It is important for a contactor to know the composition of the material because it effects the degree of pumping difficulty, pumping distance attainable without utilizing a booster pump, size of spoil area required and the percent of solids that can be pumped at any one time. The following is an outline of common materials.
   1. Sand: Hard packed or loose and denoted by gain size
   2. Shell: Loose or attached to the bottom and denoted by size
   3. Silts: Muddy material that can be organic or non-organic in composition
   4. Clay: wide varity of clays composed of differing material, generaly considered more difficult to cut
   5. Fines: Byproduct of mining operations
   6. Sludge: Byproduct of industrial or water/sewer treatment facilities
   The list provided are general categories and is not meant as a complete text. Part of a project investigation is to identify and substantially classify the material to be dredged. The material designation affects all other components of the job.
5. Angle of Repose: denotes the degree of slope angle and contour that the remaining bottom material will ultimately assume once the dredging cut is completed. The bottom material angle of repose characteristics, directly affect the side slopes of a dredge cut. Some material such as clay has a tendency to stand up well, leaving the shape of the bottom cut relatively intact over time. Material such as light slit may take a radical angle of repose thus flattening the dredge cut relativity quickly. Although many variables go into determining specific angles of repose Bull Dredging will work with you in providing a guideline for the type material to be excavated from your project.
6. Side Slopes: this term is used when discussing the width and depth that a dredge cut ideally should be, to maintain the projects desired results. A side slope is specifically the amount of material that is displaced outside of the dredge cut after the intended material has been excavated. The specific angle of repose assumed by the material will effect the side slope displacement, as will currents, tides, wave action, etc.
7. Over Dredging: This term applies to the amount of material that is excavated during operations that is over and above the contracted cubic yards (Y3). It is usual and customary to allow and “permit for” a specific amount of over dredging depth to assure contract compliance. In most cases between one half and one foot of over dredging depth is allowable and the cubic yard (Y3) price for the over dredged material is determined at contract signing.
8. Spoil Areas: This is the area in which the dredged material is pumped to and allowed to de-cant. Spoil areas are generally earthen impoundments constructed using dikes. A weir structure / flash board raiser or pumps are used to drain the return water (supernatant) from the impoundment. Spoil areas are also referred to as de-watering areas. The size of the area is necessitated by the amount and type of material that is going to be placed within it.
   1. If your project site does not have suitable land to place a spoil area, several alternative methods of material disposal are available. Tankering overland or barging to an off-site disposal zone are options as are the use of frac tanks, geo-textile tubs, hydro-cyclone, and dry pressing. (Contact our office for further information regarding alternative spoil material disposal.)
   2. Advisory - The proper planning, placement and construction of a spoil area or its alternative is paramount to a successful project and requires a level of expertise. Bull Dredging’s staff will gladly discuss the options with you to avoid pitfalls during your dredging project.
   3. Helpful hint for residential canal neighborhoods and marinas - We are all aware that the value of natural waterfront property is increasing. As they say, they are not making anymore! A dedicated spoil area site will pay for itself many times over in the long run, as your waterways can be dredged economically and maintained in pristine condition. Consider using your spoil area site as a park or parking facility when not in use for dredging operations. Furthermore, the dredge fill material can often be used for landscaping.