Rivers: Vegetation |
Back to Applications index |
|
Submerged vegetation is an important component of the riverine habitat. Substrate is intimately linked to flow, sedimentation, invertebrate and vertebrate composition and submersed vegetation.
Analysis of acoustic response of submerged aquatic vegetation (SAV) enables reporting of plant presence and absence, bottom coverage, and plant height. SAV data can be collected simultaneously along with that for bathymetry, fish, and bottom substrate classification.
|
Case Studies
|
Comparison of Acoustic and Aerial Photographic Methods for Quantifying the Distribution of Submersed Aquatic Vegetation in Sagamore Creek, NH |
|
Maintenance dredging in the Black Channel portion of the Portsmouth Harbor and Piscatiqua River Federal Navigation Project in Portsmouth (commonly referred to as Sagamore Creek) occurs in close proximity to submersed aquatic vegetation (SAV). Species, density, and spatial distribution are of concern to resource agencies given the potential impacts associated with dredging activities including the physical removal of vegetation as well as increases in turbidity and/or siltation. A variety of techniques are available for determining these attributes, including manual sampling, aerial photographic surveys, and acoustic-based surveys. Aerial photography is a standard technique for characterizing SAV distribution and, under some conditions, distinguishing species. It may underestimate SAV coverage if water clarity is low or there is poor contrast between SAV and adjoining bottom material. Acoustic surveys employ the acoustic reflectivity of the SAV for detection and for determining canopy geometric characteristics. Although acoustic techniques are not limited by water clarity, they are typically unable to distinguish species. Both photographic and acoustic techniques require some physical ground-truth sampling to verify interpretation and output. In preparation for scheduled maintenance dredging in Sagamore Creek, near Little Harbor, NH, SAV surveys were scheduled. During coordination meetings to plan these surveys, the validity of the height-based rule for distinguishing eelgrass from marine macroalgae was questioned. Accordingly, a study was planned to compare an acoustic-based estimate of eelgrass distribution with that from aerial photography. In particular, the effect of the acoustic-based plant height discriminant for estimating eelgrass coverage was to be evaluated in this study. |
|
Document Links:
Comparison of Acoustic and Aerial Photographic Methods for Quantifying the Distribution of Submersed Aquatic Vegetation in Sagamore Creek, NH
|
Product Link:
DT-X
|
|
Developing Plans for Managing Invasive Aquatic Plants in Mississippi Water Resources |
|
Invasive aquatic plants are an ever-growing nuisance to water resources in Mississippi and the
rest of the United States. These plants are generally introduced from other parts of the world,
some for beneficial or horticultural uses. Once introduced, they can interfere with navigation,
impede water flow, increase flood risk, reduce hydropower generation, and increase
evapotranspirational losses from surface waters. Invasive species also pose direct threats to
ecosystems processes and biodiversity. All agencies and individuals responsible for water
resources in Mississippi should be prepared for invasive aquatic plants through developing an
aquatic plant management plan. Components of a plan include: Prevention, Problem
Assessment, Project Management, Education, Monitoring, Site- or problem-specific management
goals, and Evaluation. |
|
Document Links:
Developing Plans for Managing Invasive Aquatic Plants in Mississippi Water Resources
|
Product Link:
DT-X
|
|
Developing Plans for Managing Invasive Aquatic Plants in Mississippi Water Resources |
|
Invasive aquatic plants are an ever-growing nuisance to water resources in Mississippi and the
rest of the United States. These plants are generally introduced from other parts of the world,
some for beneficial or horticultural uses. Once introduced, they can interfere with navigation,
impede water flow, increase flood risk, reduce hydropower generation, and increase
evapotranspirational losses from surface waters. Invasive species also pose direct threats to
ecosystems processes and biodiversity. All agencies and individuals responsible for water
resources in Mississippi should be prepared for invasive aquatic plants through developing an
aquatic plant management plan. Components of a plan include: Prevention, Problem
Assessment, Project Management, Education, Monitoring, Site- or problem-specific management
goals, and Evaluation. |
|
Document Links:
Developing Plans for Managing Invasive Aquatic Plants in Mississippi Water Resources
|
|
|
Innovative Techniques for Improved Hydroacoustic Bottom Tracking in Dense Aquatic Vegetation |
|
The basis for acoustical bathymetric surveys is detecting and timing the echo from a short, vertically oriented pulse. The exact detection process may vary from system to system but is usually based on exceedence of some minimum threshold intensity and peak width. For bathymetric surveys of navigation channels, this approach usually works well. A typical navigation channel consists of open water above a distinct sediment interface, leading to no ambiguity in relating the time of the echoed pulse to the exact depth of the sediment interface. A decided exception to this occurs when the bottom is colonized with submersed aquatic vegetation. Under these conditions, the acoustical reflectivity of the gas-filled plant stems or blades generates an echo that arrives at the receiver before the true bottom echo. Depending on plant type, height, and density, these plant-generated returns may pass the test for the detected bottom and be declared as the bottom, underestimating the true depth. If undetected, this condition can lead to erroneous surveys of channel depth and overestimates of dredging quantities required to keep the channel at its authorized depth. |
|
Document Links:
Innovative Techniques for Improved Hydroacoustic Bottom Tracking in Dense Aquatic Vegetation
|
Product Link:
DT-X
|
|
Mapping Submerged Aquatic Vegetation with GIS in the Caloosahatchee Estuary: Evaluation of Different Interpolation Methods |
|
This article evaluates different spatial interpolation methods for mapping submerged aquatic vegetation (SAV) in the Caloosahatchee Estuary, Florida. Data used for interpolation were collected by the Submersed Aquatic Vegetation Early Warning System (SAVEWS). The system consists of hydro-acoustic equipment, which operates from a slow-moving boat and records bottom depth, seagrass height, and seagrass density. This information is coupled with geographic location coordinates from a Global Positioning System (GPS) and stored together in digital files, representing SAV status at points along transect lines. Adequate spatial interpolation is needed to present the SAV information, including density, height, and water depth, as spatially continuous data for mapping and for comparison between seasons and years. Interpolation methods examined in this study include ordinary kriging with five different semivariance models combined with a variable number of neighboring points, the inverse distance weighted (IDW) method with different parameters, and the triangulated irregular network (TIN) method with linear and quintic options. Interpolation results were compared with survey data at selected calibration transects to examine the suitability of different interpolation methods. Suitability was quantified by the determination coefficient (R2) and the root-mean-square error (RMSE) between interpolated and observed values. The most suitable interpolation method was identified as the one yielding the highest R2 value and/or the lowest RMSE value. For different geographic conditions, seasons, and SAV parameters, different interpolation methods were recommended. This study identified that kriging was more suitable than the IDW or TIN method for spatial interpolation of all SAV parameters measured. It also suggested that transect data with irregular spatial distribution patterns such as SAV parameters are sensitive to interpolation methods. An inappropriate interpolation method such as TIN can lead to erroneous spatial representation of the SAV status. With a functional geographic system and adequate computing power, the evaluation and selection of interpolation methods can be automated and quantitative, leading to a more efficient and accurate decision. |
|
Document Links:
Mapping Submerged Aquatic Vegetation with GIS in the Caloosahatchee Estuary: Evaluation of Different Interpolation Methods
|
Product Link:
EcoSAV
|
|
Operating Instructions Manual for the Acoustic-Based Submeresed Aquatic Plant Mapping System |
This brief instruction set is intended to serve as a guide for the use of the ERDC-developed
Submersed Aquatic Vegetation Early Warning System (SAVEWS) embodied in the Biosonics
DT-X sounder with a Leica MX-420 DGPS Navigation System and a Panosonic Toughbook
computer. Instructions are written around the Biosonics Visual Acquisition software (version
5.0.3), Biosonics EcoSAV software (version 1.0) which contains the windows SAVEWS
software, and the Leica MX-420 software (version 1.5). These instructions are not intended to
replace the separate instruction manuals for these components. Rather, the user is encouraged
to study these separate manuals and to use this instruction set as a reminder during field
operations. |
|
Document Links:
Operating Instructions Manual For The Acoustic-Based Submersed Aquatic Plant Mapping System
|
Product Link:
EcoSAV
|
|
Use of Acoustics for Detecting Aquatic Vegetation (7.1) |
Underwater acoustics can be used for monitoring and mapping of ecosystem. Information on bottom substrata and also
on submerged aquatic vegetation is encoded in echo signal. This information can be decoded from survey data as well
as information on fish and plankton distribution and size. BioSonics has developed two sets of algorithms and data
analysis software packages for this purpose: (a) SAVEWS (Submerged Aquatic Vegetation Early Warning System) was
developed under joint research program with USACE and (b) VBT (Seabed Classifier). In both programs we started
with theoretical studies on appropriate method of echo signal processing. The second step was testing of various
processing algorithms by acquiring ground truth (verified) data on submerged plants and bottom categories using digital
echosounders DT series. After testing of processing algorithms we developed user-friendly software packages. Survey
data can be acquired in geographical context and survey maps can be generated. Echo signal processing algorithms are
described (see document link). Detection performance of the system and few case studies in marine environment and also in freshwater are
discussed. |
|
Document Links:
Use of Acoustics for Detecting Aquatic Vegetation
|
Product Link:
EcoSAV
|
|
