Salhouse Broad is a well-known and favoured destination for recreational boaters and tourists visiting the Norfolk and Suffolk Broads. Downstream along the River Bure from Wroxham, often referred to as “The Capital of the Broads”, Salhouse Broad receives high levels of boating traffic with visitors making use of the public areas along the southern bank.
It is therefore important to monitor the silt levels within Salhouse and access channels for potential hazards to navigation and to inform potential maintenance dredging operations. The Norfolk and Suffolk Broads present a challenging environment in which to conduct bathymetric surveys due to a number of factors including, but not limited to: dense patches of aquatic vegetation, underwater obstacles (E.g. wrecks and fallen trees), signal obscuration from overhanging trees and shallow water depths across much of the National Park.
Blessed with a sunny autumnal day, Exo Environmental performed a bathymetry survey, deploying a dual-frequency Echotrac CV100 echosounder. This equipment performed exceptionally well, successfully and accurately measuring depths as shallow as 0.3m, whilst differentiating between the hard, underlying geology and soft, accumulated surface silts. From mobilization to demobilisation, the survey took ~5 hours to complete, covered an area of ~75,000 m2 and required 4 cups of coffee!
A thorough GIS study of Blakeney Channel was requested to complement a recent aerial and
topographic survey of the site, conducted by Exo Environmental. Comparing previous survey records
with historical aerial photography, provided by the Historic England Archives, this work was to allow
changes to the channel morphology and saltmarsh extent over the last 70 years to be identified.
Using our specialist GIS software, historic saltmarsh extents could be overlain with our recent high
resolution Unmanned Aerial Vehicle (UAV) (drone) survey data, to locate and quantify losses and
gains of this protected habitat. Of particular note, was the growth of approximately 0.5ha of
saltmarsh following the rerouting of a drainage rill in the 1990’s, resulting in significant meandering
of the Channel.
Channel cross-section datasets from previous survey efforts dating back to the early 1980’s were
also digitised from paper drawings supplied, some of which contained limited, erroneous or
inaccurate data. Two methods were employed to correct the historic data using: georeferencing,
distances quoted on hand drawn maps, changes in saltmarsh extent and accurate topographic data
obtained during our survey of the Channel. Utilising these methods allowed us to maximise accuracy
of the digitised datasets and facilitate future comparative studies and long-term management of the
Waterside Marina is situated within a high end riverside residential complex, within Brightlingsea Harbour on the River Colne Estuary in Essex, UK, and provides moorings and shore side facilities for recreational vessels and boat owners. In 2015, 11,000m3 of accumulated sediments were removed during a major dredging campaign, with the arising sediments being dispersed on the ebb tide. Following this work, the Brightlingsea Harbour has taken responsibility for the site, which includes undertaking regular maintenance dredging to prevent the marina from silting up in the future.
To monitor siltation rates and identify target areas to focus maintenance dredging efforts, a survey was undertaken. However as the season was in full swing with high numbers of moored vessels present which limited access throughout the marina, whilst the surrounding sheet piling and high rise residential blocks satellite reception of the bathymetric and topographic GNSS positioning system was not 100%.
To overcome this issue, a combination of bathymetric and topographic survey techniques were employed to achieve the best possible results. An initial bathymetric survey was undertaken from the Exo Surveyor survey vessel in all accessible areas, subject to satellite coverage. To obtain data in areas where satellite reception was available but access was limited, a centimeter accurate GNSS topographic system on a sounding rod was deployed. In areas where both access and satellite reception were limited, a manual measurement using a graduated rod was taken to ensure 100% coverage of the marina.
Blakeney Channel is an important navigation channel that connects Blakeney Harbour to Blakeney
Town and its iconic quayside on the north Norfolk Coast. The area is dynamic and has shown some
significant morphological changes over recent decades, including; shifting sandbars, meandering of
channel centres and both eroding and accreting saltmarsh.
As part of the ongoing monitoring of the Channel and to facilitate the long-term management of
safe navigation channels within Blakeney Harbour, the Blakeney Channel Coastal Community Team
(BCCCT) commissioned Exo Environmental to conduct an aerial and topographic survey, to
compliment and allow direct comparison with historical data sets, to identify changes to the
Channel’s morphology over recent decades.
To achieve this, a photogrammetric survey was undertaken using an aerial drone with a preprogrammed flight path and referenced to a series of ground control points placed over a range of altitudes across the study site. To support the aerial survey, topographic GNSS equipment was used as a quality check and to obtain data from areas submerged at all states of the tide. The combined dataset was used to create an XYZ grid with <1cm accuracy and a resolution of approximately 2cm per pixel. The resolution of the resultant 3D model is far superior to historic aerial and satellite imagery and comparable to that of LIDAR data accessible from the Environment Agency.
A holistic understanding of the environment is critical for the sustainable development and maintenance of infrastructure. With regards to the beneficial use of dredged material (BUDM), particularly its application in habitat creation, restoration and enhancement projects, detailed knowledge of the local topography is fundamental. This allows volume and storage calculations, matching of sources and sinks and facilitating post-works monitoring of processes that typically occur over the medium- to long- term, such as consolidation of material and biological colonisation.
As part of the Brightlingsea Dredging and Restoration project, Exo conducted dual-frequency bathymetric and unmanned aerial vehicle (UAV) (drone) photogrammetric surveys throughout the site, during high and low water spring tides respectively. The high resolution datasets were then merged across the overlapping intertidal zone (an approximate tidal range of 5m) using specialist software, to provide a comprehensive map of levels throughout the Creek.
Applying the clients requested target depths for each dredge area, accurate dredge volumes can be calculated and used to match with the storage volumes of restoration sites selected following the comparison of historic and current saltmarsh extents. In addition to project design, the data obtained also supports project planning through the identification of priority areas, provides baseline data for continued environmental monitoring and assists in the formulation of a long-term management plan for the Brightlingsea Harbour Authority. The combination of these survey techniques provides excellent data coverage for logistically challenging sites located at the landwater boundary such as the intertidal zone.