NWT RESEARCH DATABASE

Regions: Sahtu Settlement Area

Tags: physical sciences, permafrost, vegetation, hydrology

Objective(s): To characterize the hydrology of an alpine valley’s landscape Types (LTs) and how they affect storage and runoff responses to precipitation.

Project Description: The goal of this thesis is to characterize the hydrology of an alpine valley's landscape Types (LTs) and how they affect storage and runoff responses to precipitation through the following four research objectives: 1) a physical description of LTs composing an alpine study catchment that are expected to exhibit distinct hydrological responses to precipitation inputs; 2) a physical description of water routing and storage responses within and among the LTs in the catchment; 3) a water-balance assessment of the -0.5 km2 study catchment; and, 4) a remote sensing assessment of historical trends in LT proportions and positions within the surrounding 1757 km2 study area. Each landscape type (LT) will have surface and subsurface conditions estimated based on measurements taken along 5 60m long transects. Measurements will include snow water equivalent (SWE), assessed weekly at 30 randomly selected locations along each transect with a snow tube and hanging scale. Daily measurements of snow melt during the freshet will be made with snow lysimeters in each LT and ablation wires. At 3 locations along each transect, ice at the snowpack base will be measured in snow pits, along with moisture content (MC) and temperature profiles throughout the snowpack. Following snowmelt, soil thaw depth will be measured weekly with frost probes at the same randomized locations. Where frost probes are ineffective due to rocky substrate, Electrical Resistivity Tomography (ERT) transects will be run along each transect in early June and late August so frost table depth can be estimated. ERT was chosen as a non-intrusive option compared to other geophysical imaging techniques, such as seismic testing. Vegetation will also be documented every meter along each transect following snowmelt. Soil characteristics of shallow (<30cm) and deep (>30cm) layers will be assessed at 5 random locations along each transect by taking samples to weigh under field conditions, saturated conditions, and constant weight conditions following oven drying. Three Observation wells made of 3 inch diameter PVC will also be installed at ~0.5-3m depth at 30m internals along each transect to assess Hydraulic conductivity (K) in late August, based on bucket tests. Water level recorders (WLRs) installed in each observation well will provide 30 minute average values to assess changes in hydraulic head throughout the thaw season (May-August) and in response to rain events. Three extra PVC pipes will be used as piezometers, assessing water pressure at 1, 2, and 3m depth below the channel fen to confirm if the stream is being fed groundwater from below (positive pressure) or draining downward (negative pressure). Field capacity and infiltration rates will also be assessed with falling-head ring infiltrometers installed ~2m from a central location along each transect. Evapotranspiration (ET) rates of each LT will be estimated with soil lysimeters, small buckets filled with local soil taken from each LT and installed level with the surrounding area. Lysimeter weight and MC will be checked daily and adjusted as necessary to match 5 MC sample points tested with a Hydrosence II probe in the neighbouring soils. An evaporation pan will also be used to estimate ET of open water within the basin. Mean slope values will be assigned to each representative LT containing a study transect with a digital elevation model generated from unmanned aerial vehicle (UAV) photos. UAV will also develop estimates of albedo based on spectral characteristics of each representative LT and the net radiometer measurements taken on organic-rich elevated terrain. Percent basin area will be estimated visually with UAV images and polygons created with ArcMap coded to their respective LT. Changes in 2H and 18O isotope ratios in water will be sampled from fresh snow, snowmelt, and rain collected from snow pits, snow lysimeters, and tipping buckets respectively. These samples will provide the signature isotope ratios of ‘new’ water entering the basin. In comparison, ‘old’ water stored in the catchment should have a different isotopic signature measurable during baseflow conditions from the main stream in early April. Isotope ratios will be analyzed with mass spectrometry while salinity and temperature will be assessed in the field with conductivity and temperature probes. In April, samples will be taken at 2 additional upstream locations to assess if there are different of isotope and salinity signatures from different groundwater sources. Finally, a weather station will be installed with an accompanying solar panel stand to support the datalogger, power source, and series of instruments required to measure atmospheric conditions including net radiation, rain, snow depth, temperature, relative humidity, wind speed and direction. A summary report of field activities can be prepared on an annual basis if this would be helpful. Brief updates can also be given during the SRRB monthly teleconference calls. Meetings and presentations can be arranged in Tulita and/or Norman Wells at the conclusion of this project. Publications resulting from this research will be provided to the appropriate body as digital and/or paper copies. The fieldwork for this study will be conducted from August 27, 2020 to September 10, 2020.