Evaluation of stream and wetlands restoration using 2 UAS-based thermal infrared mapping

: Unoccupied aerial systems (UAS) are now routinely used for collecting aerial imagery and 18 creating digital surface models (DSM). Lightweight thermal infrared (TIR) sensors provide another payload option for generation of sub-meter resolution aerial TIR orthophotos. This technology 20 allows for the rapid and safe survey of groundwater discharge areas, often present in inaccessible 21 or dangerous terrain. Aerial TIR water-surface data were collected March 2019 at Tidmarsh Farms, 22 a former commercial cranberry bog located in coastal Massachusetts, USA (41°54'17.6"N 23 70°34'17.4"W), where stream and wetland restoration actions were completed in 2016. Here we 24 present a 0.4 km 2 georeferenced, temperature calibrated TIR orthophoto of the area. The image 25 represents a mosaic of nearly 900 TIR images captured by UAS in a single morning with a total flight 26 time of 36 minutes, and is supported by a DSM derived from UAS visible imagery. The survey was 27 conducted in winter to maximize temperature contrast between relatively warm groundwater and 28 colder ambient surface environment; lower-density groundwater rises above cool surface waters 29 and thus can be imaged by a UAS. The resulting TIR orthomosaic shows fine detail of seepage 30 distribution and downstream influence along the several restored channel forms, which was an 31 objective of the ecological restoration design. The restored stream channel has increased 32 connectivity to peatland groundwater discharge, reducing the ecosystem thermal stressors. Such 33 aerial techniques can be used to guide ecological restoration design and assess post-restoration outcomes, especially in settings where ecosystem structure and function is governed by 35 groundwater and surface water interaction.

conducted in winter to maximize temperature contrast between relatively warm groundwater and 28 colder ambient surface environment; lower-density groundwater rises above cool surface waters 29 and thus can be imaged by a UAS. The resulting TIR orthomosaic shows fine detail of seepage 30 distribution and downstream influence along the several restored channel forms, which was an 31 objective of the ecological restoration design. The restored stream channel has increased 32 connectivity to peatland groundwater discharge, reducing the ecosystem thermal stressors. Such

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At temperate latitudes, cold water anomalies in summer and warm water anomalies in winter 43 can indicate zones of spatially preferential groundwater discharge that can be mapped with ground-44 based TIR at high spatial resolution compared to more traditional groundwater discharge-45 characterization methodology (Briggs & Hare, 2018). Unoccupied

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Recently, there has been a movement to better incorporate ecological services and functions into 58 stream and wetland restoration projects (Hester & Gooseff, 2010). Hydrological processed-based 59 wetland restoration requires understanding site-wide hydrodynamics, which often involves scaling-

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UAS-based imaging offers the potential to plan and evaluate process-based wetland restoration 74 projects efficiently, with the combined collection of visible, DSM, and TIR data. However, the 75 approach requires sufficient contrast between the temperature of the surface environment, and 76 groundwater temperature; enough to allow the TIR sensor to resolve the groundwater as relatively 77 warm (winter), or cool (summer). The use of TIR-equipped UAS to map high-temperature

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The objectives of the study were to evaluate i) the ability of TIR-equipped UAS for identifying 86 groundwater discharges, and ii) the usefulness of TIR-equipped UAS as a tool for validating thermal 87 refugia goals of process-based restoration.

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The study area, Tidmarsh Farms, is a former 2.5 square-km cranberry bog that underwent a

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The flight plan was developed using UgCS ® software. The UgCS photogrammetry tool was

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The five values were averaged to give a best estimate of the water surface temperature of each

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Figure 6 provides close-up views of the TIR imagery, with colors adjusted to provide more 219 contrast at the warmer end of the temperature scale (more clearly shows groundwater input). Note 220 i) warm groundwater discharge is clearly discernible from the relatively cooler surface waters ( Figure   221 6a), ii) seepage zones distributed along the reconstructed stream channel (Figure 6b), and iii) discrete 222 seeps within the stream channel are clearly identifiable (Figure 6c).

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Before the restoration, ground based TIR (Figure 1) showed that "wet areas", long known by 225 farmers (Figure 2), were due to groundwater seeps, likely due to the thin peat in this area (rather than

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Groundwater temperature is also a factor. The northeastern USA has a typical continental

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Our results show how UAS-based aerial TIR can be applied to mapping groundwater seeps in 258 wetlands. This approach provides a viable alternative to ground-based seep identification methods

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(i.e. ground-based TIR or direct temperature measurements), particularly at the scale of this survey.

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Depending on survey size, UAS may provide a less labor-intensive solution, with spatial coverage

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(2017) that predicted preferential groundwater discharge upward through the peatland platform based on the 297 underlying topography of the sand-peat aquifer interface.

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The primary objective of the study was to determine if the engineered stream channel at 311 Tidmarsh Farms had successfully intercepted groundwater seepage, compared to relic farm channels.

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The TIR-equipped UAS was able to image the entirety of the restored channel area in a single 313 morning. Results show the reconstructed stream channel is warmer along its entire length, indicating 314 spatially contiguous groundwater connectivity. Therefore, the groundwater discharge 'processed 315 based' restoration design was successful in this regard, and likely creates thermal refugia for aquatic 316 habitats. Further, the DSM extracted from visible imagery was useful in efficiently mapping the 317 restored channel forms (compared to ground-based surveys).

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Our results show how TIR-equipped UAS can be applied to mapping groundwater seeps in 320 wetlands. This approach provides a viable alternative to ground-based seep identification methods

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(i.e. ground-based TIR or direct temperature measurements), particularly at the scale of this survey.

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Depending on survey size, UAS may provide a less labor-intensive solution (<1 hr rather than 323 multiple days), with far greater spatial coverage than ground-based methods, particularly when site