Surveying

Data before you dredge is a vital step.  An unsuccessful dredging project may quickly end because of poor planning and not knowing what to expect below the water surface.  Bathymetric surveying usually refers to mapping the top of the surface below the water surface.  Water depths are an important aspect when planning where to dredge, if a dredge will have enough water to float, or how far to lower the water level.  Hydrographic surveying is a broader term that includes mapping both the water depth and sediment characteristics. Sedimentation surveys will include the location and depth of sediment relative to the water surface and most of the time the hard-pan (original lake bottom) that is typically denser composition material (clay, rock, liner, etc.).  Surveys may include core sampling to determine the density, composition, particle size distribution, and other sediment characteristics by depth.  Depending on the project you may only need a certain set of data to base your dredging project on.  Surveying can also help identify issues common with dredging such as coarse debris, uneven surfaces, stumps/logs, and other anomalies.  River Sand can collect samples using Vibracore, various hand-held sediment samplers, sludge judge, or even an Eckman dredge/sampler.  We have our own soil laboratory and work with several independent laboratories for analysis.

River Sand can provide a professional survey with sub-centimeter accurate data points.  But you may be wondering how I can just get an idea of how much is beneath the surface.  One way to estimate the muck below the water is to use the simple formula for determining any volume – length x width x height.  Generally finding an area of an impacted area can be done using measurements from aerial images with a scale or measurement tool prior to even getting in the water.  An alternative is using a measuring tape (300’ are common most hardware stores) or even better a range finder (common in hunting and golf applications).  Once you determine the area you would like to survey, the next step is to determine the depth of sediment.  There are methods for calculating volume on a grid system but that gets complicated.  Usually, an average depth is best even if you need to break your single areas into multiple areas with differing depths.  To measure the depth, use a probe 1” or less in diameter (wooden handle, rebar, pvc pipe, etc.) and work it into the sediment until you feel a consolidated (hard) bottom.  You can measure the sediment depth by subtracting the difference in the water depth to the top of the sediment.  Remember to convert feet to yards or vice versa before multiplying to get your estimate.

This method can give you an idea of the volume you need to remove and the increase in water depth you may be achieve with dredging.  However, this is not a method for basing a project or a contractual agreement upon.  We have seen a lot of projects not get what they paid for because they lack the information confirming that the agreed upon amount has been removed after dredging is completed.  Surveying or confirmation of some type should always be an important part of your dredging project.

River Sand, inc. can provide mapping, surveying, core sample collection and analysis.  Results can be provided with technical specifications or in a manner for homeowners to view and understand suitable for presentations.  We include much of our mapping and surveying within the dredging project cost.  The quality of our survey results are backed with QA protocols and reviewed by an engineer.  Many surveys may look good on paper but the methods and equipment do not provide suitable restraints for accurate results.  River Sand understands the benefits of a great survey, and uses them to make certain you get what you pay for with your dredging project.

This method can give you an idea of the volume you need to remove and the increase in water depth you may be achieve with dredging.  However, this is not a method for basing a project or a contractual agreement upon.  We have seen a lot of projects not get what they paid for because they lack the information confirming that the agreed upon amount has been removed after dredging is completed.  Surveying or confirmation of some type should always be an important part of your dredging project.