Identifying groundwater discharge zones in the Central Mackenzie Valley using remotely sensed optical and thermal imagery

Landsat 4–5 Thematic Mapper, Landsat 8 Operational Land Imager, and RapidEye-3 data sets were used to identify potential groundwater discharge zones, via icings, in the Central Mackenzie Valley (CMV) of the Northwest Territories. Given that this area is undergoing active shale oil exploration and climatic changes, identification of groundwater discharge zones is of great importance both for pinpointing potential contaminant transport pathways and for characterizing the hydrologic system. Following the work of Morse and Wolfe (2015), a series of image algorithms were applied to imagery for the entire CMV and for the Bogg Creek watershed (a sub watershed of the CMV) for selected years between 2004 and 2017. Icings were statistically examined for all of the selected years to determine whether a significant difference in their spatial occurrence existed. It was concluded that there was a significant difference in the spatial distribution of icings from year to year (α = 0.05), but that there were several places where icings were recurring. During the summer of 2018, these recurrent icings, which are expected to be spring sourced, were verified using a thermal camera aboard a helicopter, as well as in situ measurements of hydraulic gradient, groundwater geochemistry, and electroconductivity. Strong agreement was found between the mapped icings and summer field data, making them ideal field monitoring locations. Furthermore, identifying these discharge points remotely is expected to have drastically reduced the field efforts that would have been required to find them in situ. This work demonstrates the value of remote sensing methods for hydrogeological applications, particularly in remote northern locations.

118 spring type, and river type (Carey, 1973;Yoshikawa, 2007). River icings, which form 119 when water discharges through a body of river ice and laps onto a frozen river surface, 120 are not considered in this study. Only land-fast (spring and ground type) icings are 121 considered. These two types of icings, conceptualized in Fig. 2 and 3, are groundwater 122 sourced and can be differentiated by whether they occur from a permanent spring or 123 from a temporary seep (Carey, 1973;Pollard and van Everdingen, 1992). Spring icings 124 are formed from groundwater springs, where water tends to be sourced from sub-      268 The groundwater flow system within the Bogg Creek watershed is expected to consist of 269 regional to local flow regimes controlled largely by permafrost distribution. Regional flow 270 systems are hypothesized to originate along the southwestern limb of the geologic 271 syncline and in the foothills of the Mackenzie Mountains. Groundwater is hypothesized 272 to flow through taliks, and discharge as springs and into waterbodies in the watershed.
273 Regional flow may also originate in the northeast from the Franklin Mountains, which 274 form the eastern limb of the regional syncline. Local flow is hypothesized to occur in 275 supra-permafrost zones and shallow taliks, through mineral and organic soils. This   Table   286 1. These three years were selected as imagery was available for the desired season 318 Values in excess of the threshold were considered to be ice and were extracted from 319 the image.

321
The MDSII extracts all ice in the study area, including ice on water bodies that may not 322 have been completely melted. In order to remove this ice from the result, a water mask 323 was generated using an image from the summer of that year (shown in Table 1). As the 324 extent and location of thaw ponds and thermokarst lakes are expected to be variable

364
365 First, digital numbers were converted to spectral radiance: (shown in Table 2) (shown in Table 2)   504 Then, each of the two-year combinations were intersected to determine the percentage 505 of recurring icings. All three years were also intersected to determine which icings would 506 be most likely to recur again in the future. It was found that approximately 12.5% of the 507 icings recur in all three years, and therefore are more likely to be of spring type. These 508 icings represent the most promising field monitoring locations within the CMV. Fig. 11 509 shows the icing overlap distribution for each year combination. Though the overlap 510 range for all three years represents only the minority of icings, it is noted that the entire   Table 3). icings falling in the weak warm category (1 > z > 0) may be discharging enough warm 583 groundwater to fall above the mean temperature, but not enough to appear in the strong 584 warm. Similarly, the icings falling in the weak cold category (-1 < z < 0) may affect the 585 LST enough to fall below the mean, but not enough to appear in the strong cold 586 category. In theory, it is possible that the mean of the data (the 0-level z-score) could 587 distinguish ground from spring icings, however, the results provide insufficient evidence 588 to support this conclusion. If an icing were classified as spring type because it fell just 589 above the mean z-score of 0, it may in fact be a ground icing that is still discharging 590 warm water in the late winter or that has a low ice content. The same argument may be 591 made for an icing classified as ground type because it fell just below the mean. Perhaps 598 be more definitively classified as either spring or ground type based on current 599 definitions of their physical occurrence, but because the majority do not fall into these 600 strong anomalies, it is concluded that thermal anomalies may not be an ideal variable 601 for discriminating icing type at this resolution. The spatial resolution of the Landsat 602 thermal band is only 120 m (re-sampled to 30m) and therefore may be too coarse to 603 detect temperature changes resulting from groundwater discharge. This is especially 604 true when the discharge locations are small and discrete, as they seem to be in this  Table 1), selection of cloud-free images, selection of images taken at the same time 616 of day, and temperature standardization.     D r a f t Coordinates provided with reference to outset map.
D r a f t D r a f t Figure 3. Conceptualization of a ground icing where S w is the saturation of water and S θ is the residual saturation of water (maximum saturation of ice). In early winter, an upward vertical hydraulic gradient is imposed in sandy sediment (low frost susceptibility) by the progressing freezing front and relatively less permeable sediment (ex. silt) surrounding it. The freezing front has progressed further in the silt due to its higher frost susceptibility. By mid-winter, the icing has reached peak formation and the freezing front has progressed to such a depth that vertical flow no longer exists.
D r a f t      D r a f t Figure 14. Piper Plot of site-wide endmembers, including supra-permafrost groundwater (star), and sub-permafrost groundwater (X). Spring waters (green circles), collected from the GL sites described in Table 3, plot primarily within the Ca-HCO 3 facies but display high concentrations of Na and Cl with very little SO 4 , making them unique within the watershed. Spring water appear to fall between supra-permafrost and sub-permafrost endmembers, though its origin cannot yet be definitively determined.