THEW BLOG

Surveying and Mapping Procurement Tips for Solar Development Projects

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Due in large part to aggressive renewable energy goals and the push for decarbonization, the solar industry is booming in New York State. Over the past few years, Thew Associates has served as the land surveying consultant for numerous community and utility scale solar developments throughout New York, Massachusetts and Vermont. As with most land development projects, topographic, utility, and boundary retracement surveying and mapping are essential components for the development of a solar project. The following are few items solar developers should consider when procuring professional surveying and mapping services.

  1. Procurement

Some solar developers look to their environmental permitting and/or site/civil consultant to procure the surveying and mapping for a project. While it may seem convenient to have the design professional subcontract with a professional land surveyor, there are strategic advantages for the developer to retain control of the professional land surveyor.

  • Decreased Project Costs: Procuring the surveyor directly eliminates the mark-up (frequently 10%) the design professionals typically include cost for utilizing a subconsultant and management costs to cover the time necessary to manage the surveying subconsultant.
  • More efficient project management: Frequently, the Solar Developer is dealing with real estate issues such as parcel acquisition, creation of lease parcels, subdivisions, access and utility easements, commitments for title insurance. These items typically are legal matters that design professionals do not handle on a routine basis.  Therefore, the design professional simply acts as intermediary conveying information between the Developer and the Surveyor.
  1. Topography

Topographic mapping is required to facilitate site/civil design.  We are frequently asked if publicly available LiDAR can be utilized as a source for topographic information.  Our answer is typically “it depends”.  If a two-foot contour interval is sufficient for site/civil design, then yes, publicly available LiDAR may be suitable.  However, our experience is that LiDAR with a point density of ≤ 2 points per square meter (ppsm) in wooded terrain is not sufficient to meet the accuracy requirements for two-foot contours.  Public LiDAR data sets that have densities greater than 4 ppsm have proven to meet the accuracy standards for two-foot contours.

Public LiDAR data sets acquired prior to 2012, typically don’t meet the accuracy standards, especially in wooded or brushy areas.

Ground truthing and check shots are required to confirm the accuracy of public LiDAR data.

In some instances, the civil/site engineer requires topography with a one-foot contour interval for storm water and access road design, whereby ground surveys can be conducted to collect the required topographic information.

Every Developer and Design Professional should be aware that accurate breaklines and planimetric information (e.g. buildings and structures, headwalls, railroads, paved and unpaved roads, utilities, signs, etc.) cannot be extracted from LiDAR due to the density of the data set.

Depending on the size of the project and the land cover (i.e. woodlands, abandoned agricultural lands, or active agricultural lands), Thew Associates recommends acquiring topographic information suitable for 50 scale (1” = 50’) topographic mapping with a one-foot contour interval utilizing conventional surveying techniques (i.e. ground survey), UAV-mounted LiDAR and aerial photography, or manned aircraft LiDAR and aerial photography.

Ground surveys may be more economical to conduct if a site is relatively small (i.e. less than 30 acres) and is open agricultural lands, while UAV LiDAR data and aerial photography acquisition is most economical for open or wooded sites ranging from 10 to 800 acres.  Acquisition of LiDAR and aerial photography from a manned aircraft is typically more economical for larger projects ranging from 300 to several thousand acres.  The disadvantage of utilizing a manned aircraft is that data must be collected during periods of “leaf-off” without snow cover.  UAV LiDAR can be acquired in “leaf-on” conditions because of the greater point density due to the low altitude and slow speeds the UAV’s operate at.

Watch for our next topics regarding UAV LiDAR and ALTA/NSPS Land Title Surveys for Solar Developments.

UNDERWATER STRUCTURAL ASSESSMENT WITH MULTI-BEAM SONAR

Thew Associates was retained in January of 2019 by an engineering firm providing design services for the stabilization of a concrete flood wall on the northerly bank of Rondout Creek in Rosendale, New York.  The engineer required bathymetric surveying and mapping of the Creek in the vicinity of the flood wall to facilitate their design. Thew Associates collected bathymetric data utilizing a Norbit iWBMS multi-beam echo sounder mounted on a remotely controlled EchoBoat. In addition to the bathymetry, the multi-beam sonar utilized for the survey was able to confirm areas of significant scouring and undermining of the flood wall footings.

The 1.8-meter EchoBoat USV was utilized due to restricted access (steep banks), swift currents, and variable water depths.  The vessel was secured with a tether held by personnel on a bridge adjacent to the upstream end of the survey area.  The Norbit iWBMS integrated multi-beam sonar system is compact and lightweight enough to be easily used with the USV.  A simplified graphical user interface that communicates with the shore station and operator through a remote connection allows the user to navigate the USV and observe the data being collected.  Additionally, the system has the ability to transmit the data in real-time to the office so the Project Manager can also view the data being collected.

Multi-beam sonar was chosen over vertical single-beam sonar because of the ability to provide complete coverage of the Creek bottom and the ability to collect bathymetric data under the flood wall to map the extent of the undermining caused by scour beneath the flood wall footings.

During the survey, raw position and motion data was logged on the survey vessel, while GPS/GNSS observations were logged by a local base station set up over a project control point.  This data was combined and post-processed to provide very accurate positioning of each sounding, even in areas where the GPS/GNSS signals are interrupted, such as near the bridge or immediately adjacent to the flood wall.  The data was all initially post-processed and validated utilizing Hypack hydrographic surveying processing software.  The bathymetric data was subsequently exported as an XYZ file to create a representative bathymetric surface, as well as an LAS point cloud file of all soundings.  The LAS file was imported into TopoDOT to extract detailed breakline data for the flood wall, footings, extents of undermining, and adjacent concrete apron.  The breakline and surface area was brought into an Autodesk Civil 3D environment to prepare the final bathymetric mapping, including plan and cross-sectional views to illustrate the existing conditions and for use in the remedial design.

Figure1
Figure 1: Visible undermining of the concrete footing to the left of the image. The vertical section of the flood wall is seen to the extreme left of the image.

Multi-beam sonar can be used to inspect the integrity of many underwater components including:

  • Bridge piers/abutments
  • Piles
  • Retaining walls (submerged installed sheet pile retaining wall on Buffalo River project)
  • Dam structures
  • Submerged intakes/outfalls
  • Abandoned-in-place infrastructure (submerged roads/bridges, buildings, walls)
  • Breakwater armor (stone, blocks: dolos, antifer, tetrapod, etc)

Figure2
Figure 2: The flat horizontal green line is the exposed portion of the top of the concrete footing.  The blue represents the Creek bottom.

Figure3
Figure 3: The vertical flood and concrete footing is readily visible with the adjacent Creek bottom.  Scour was not occurring in this area.

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Canton

6431 US Hwy 11
Canton, NY 13617

Phone: 315-386-2776 
Fax: 315-386-1012

Utica

9478 River Road
Marcy, NY 13403

Phone: 315-733-7278
Fax: 315-797-1957

Saranac Lake

135 Broadway
Saranac Lake, NY 12983

Phone: 315-386-2776

Syracuse

5866 State Route 31 
Cicero, NY 13039

Phone: 315-244-2151

Thew Associates Land Surveyors
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