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Mounds View Stormwater Pond Assessment <br />2 METHODS <br />July 2023 <br />2.2.1 SURVEYS <br />Stantec field staff surveyed stormwater basins identified and selected by the City. The pond surveys were <br />completed in two stages: a topographic land survey above the pond's water level, and an "in -pond" <br />survey of the wet ponds using a small boat. <br />Data related to basin bathymetry, engineered structures, sedimentation, and surrounding topography <br />were collected at each site using standard survey methods described below. <br />2.2.1.1 Field Surveys <br />Field staff used a Trimble R8 survey -grade GPS unit (R8) to collect location data and elevations at <br />intervals throughout the dry basins and for ground shots above the water surface elevation surrounding <br />the wet basins. Field staff also used the R8 to obtain the invert elevations of all structures at basin inlets <br />and outlets, overflow elevations of weir structures, and water surface elevations. If tree cover was <br />excessive, the survey team set up a Rangefinder station to survey structure elevations in those locations. <br />For topography in areas with dense tree cover, Lidar was used to fill in data gaps. <br />2.2.1.2 Bathymetric Surveys <br />A "fish net" was digitally overlayed onto each wet pond using ArcGIS to provide a guide for more uniform <br />sample distribution of data. Figure 2-2 shows an example fish net for a pond in the City. <br />Field staff collected approximately one survey point within each square from a small boat. Location data <br />was collected using ArcGIS Field Maps and a mobile device. The mobile device was connected to a <br />Trimble R1 GNSS receiver using Bluetooth to collect sub -meter grade location data. At each survey point, <br />a depth to sediment reading was recorded by advancing a survey rod through the water column until the <br />top of sediment was reached and the depth was recorded. The depth to refusal was estimated by <br />advancing the same rod through the sediment to the pond bottom, or when it could no longer be pushed, <br />and recording the depth. <br />Field staff then collected a water surface elevation for each wet pond using the Trimble R8 unit. <br />8 <br />