The aim of this study was to develop an approach for estimating ice break-up dates on the Mackenzie River (MR) using more than a decade of MODIS Level 3 500 m snow products (MOD/MYD10A1), complemented with 250 m Level 1B radiance products (MOD/MYD02QKM) from the Terra and Aqua satellite platforms.
The analysis showed break-up began on average between days of year (DOYs) 115 and 125 and ended between DOYs 145 and 155 over 13 ice seasons (2001–2013), resulting in an average melt duration of ca. 30–40 days. Thermal processes were more important in driving ice break-up south of the MR confluence with the Liard River, while dynamically driven break-up was more important north of the Liard.
A comparison of the timing of ice disappearance with snow disappearance from surrounding land areas of the MR with MODIS Level 3 snow products showed varying relationships along the river. Ice-off and snow-off timing were in sync north of the MR–Liard River confluence and over sections of the MR before it enters the Mackenzie Delta, but ice disappeared much later than snow on land in regions where thermal ice break-up processes dominated.
MODIS observations revealed that channel morphology is a more important control of ice break-up patterns than previously believed with ice runs on the MR strongly influenced by channel morphology (islands and bars, confluences and channel constriction).
Ice velocity estimates from feature tracking were able to be made in 2008 and
2010 and yielded 3–4-day average ice velocities of 1.21 and
1.84
These preliminary results confirm the utility of daily MODIS data for monitoring ice break-up processes along the Mackenzie River. The addition of optical and synthetic aperture radar data from recent and upcoming satellite missions (e.g. Sentinel-1/2/3 and RADARSAT Constellation) would improve the monitoring of ice break-up in narrower sections of the MR.
The Mackenzie River basin (MRB) is the largest in Canada and is subject to one of the most important annual hydrologic events. River-ice break-up on the Mackenzie River (MR) is a process by which upstream (lower latitude) ice is pushed downstream while intact ice resists movement downstream (higher latitude) (Beltaos and Prowse, 2009). Ice break-up is defined as a process with specific dates identifying key events in space and time between the onset of melt and the complete disappearance of ice in the river. This is the definition used in previously published literature and will be applied in this paper. Break-up is often associated with flooding in north-flowing systems and is thus an important hydrologic event with many environmental benefits (e.g. geochemical land deposition and lake and groundwater recharge) and detriments (e.g. infrastructure damage and lost economic activity) (Prowse, 2001; Kääb et al., 2013). Investigations of river regimes in high-latitude countries including Canada, the United States, Russia, Sweden and Finland have a long history related to their ice monitoring (Lenormand et al., 2002). This is important as ice freeze-up and break-up records serve as climate proxies responding to changing air temperature patterns (Magnuson et al., 2000). The ice break-up process is nonetheless under-monitored. There is therefore a gap in knowledge when attempting to understand all associated hydrologic parameters due to their highly dynamic nature (Beltaos et al., 2011).
The shortage of ice observations on the Mackenzie River and other rivers and
lakes in Canada is partly the result of budget cuts, which have led to the
closing of many operational hydrometric stations (Lenormand et al., 2002).
Specifically, ice freeze-up and break-up observations peaked during the
1960–1990s and declined dramatically thereafter following budget cuts from
the federal government (Lenormand et al., 2002). In the last decade only, the
observational network of discharge and ice measurements on the MRB has
declined from 65 to 15 stations. Satellite remote sensing is a viable tool
for filling this observational gap. For example, Pavelsky and Smith (2004)
were able to monitor ice jam floods and break-up events discontinuously over
a 10-year period (1992–1993, 1995–1998 and 2000–2003) on major
high-latitude north-flowing rivers at 500 m and 1 km spatial resolutions
(the Lena, Ob, Yenisey and Mackenzie rivers) using MODIS and Advanced Very
High Resolution Radiometer (AVHRR) imagery. Similarly, Chaouch et al. (2012)
showed the potential of MODIS (0.25 and 1 km spatial resolutions) for
monitoring ice cover on the Susquehanna River (40–42
The aim of the present study was therefore to develop an approach to estimate key ice break-up dates (or events) on the Mackenzie River over more than a decade using Moderate Resolution Imaging Spectroradiometer (MODIS) data. The paper first provides a description of the procedure developed to monitor ice break-up on the MR. This is followed by a quantification of ice-off dates (spatially and temporally) provided by MODIS data. Next, average ice-off dates are compared for a 13-year period (2001–2013). Lastly, displacement of ice runs calculated with MODIS is used to estimate average ice velocity along sections of the MR.
The geographical area of this study focuses on the Mackenzie River extending
from the western end of Great Slave Lake (61.36
Northern reaches of the Mackenzie River basin (MRB), its sub-basins
and major rivers and lakes. The MRB extends from 54 to 68
Air temperature plays an important role on the timing of spring freshet (Beltaos and Prowse, 2009; Goulding et al., 2009b; Prowse and Beltaos, 2002) in the MRB. It has therefore been associated with increased flow and the initiation of ice break-up in the basin as a result of snowmelt onset (Abdul Aziz and Burn, 2006). In thermal (over-mature) ice break-up, there is an absence of flow from the drainage basin earlier in the melt season, and the ice remains in place or is entrained in flow until incoming solar radiation disintegrates the river ice increasing water temperatures (Beltaos, 1997). This slow melting process causes a gentle rise in discharge on a hydrograph, with flooding found to be less frequent during that period (Goulding et al., 2009a). In dynamic (premature) ice break-up, the accumulation of snow on the drainage basin is higher and the stream pulse (or spring freshet) from snowmelt is characterized by a high slope on the rising limb of the hydrograph (Goulding et al., 2009b; Woo and Thorne, 2003). In the presence of thick ice downstream, flow can be impeded causing a rise in backwater level and flooding upstream. However, when ice resistance is weak downstream, stress applied on the ice cover can rise with increasing water levels fracturing and dislodging ice from shorelines continuing downstream, eventually disintegrating downstream (Hicks, 2009). This process can continue until certain geometric constraints such as channel bends, narrow sections and islands can stop the ice run causing ice jams (Hicks, 2009). Here, the wide-channel jam is the most common of dynamic events which develops from the flow shear stress and the ice jams' own weight, which is formed by the collapse and shoving of ice floe accumulation and is resisted by the internal strength of the accumulation of ice flows (Beltaos, 2008). As the jam builds with ice rubble, the upstream runoff forces can increase above the downstream resistance, thus releasing the jam and creating a wave downstream that raises water levels and amplifies flow velocities (Beltaos et al., 2012). Observations have shown an initial increase and final decrease in water levels as wave celerity and amplitude attenuates downstream (Beltaos and Carter, 2009). In general, thermal decay and ice break-up processes continue downstream after the ice jam release (Hicks, 2009). MODIS imagery has also shown the timing of spring flood and location of open-water tributaries to have the most impact on ice break-up processes (Pavelsky and Smith, 2004).
Illustration of the processing steps of ice of observations (manually and by visual interpretation) on the Mackenzie River.
A processing chain was developed in order to determine ice presence or
absence (open water) on the Mackenzie River. As seen in Fig. 2, MOD/MYD10A1
Level 3 (primary data set, 500
Through visual interpretation varying land attributes digital number (DN) values (snow, river ice, cloud, open water) in the MOD/MYD02QKM were defined from MOD/MYD10A1 scientific data set (SDS) values of the same land attributes. Observing and comparing the same areas of interest and dates from MOD/MYD10A1 and MOD/MYD02QKM images as seen in Table 2 completed this process. For example, MOD/MYD10A1 images of ice cover at a SDS reading of 100 (river ice) was matched to a DN value ranging from 40 to 110 from the MOD/MYD02QKM images.
MODIS images, for the period from 1 week before to 1 week after the ice
break-up period had ended over the MRB from 2001 to 2013, were downloaded
from the National Aeronautic and Space Administration's (NASA) Earth
observing System Data and Information System (EOSDIS)
(
The use of the L3 data product from a single MODIS sensor (Aqua or Terra) limited the potential to obtain frequent ice break-up observations as a result of cloud cover conditions. However, using L3 product from both Aqua and Terra satellites across varying orbital tracks in combination with the L1B product greatly increased the number of observable events during the ice break-up period, up to more than 90 % of available images (Table 3). MODIS acquisitions from both the Aqua and Terra satellites doubled the number of images available during clear-sky conditions. In addition, the availability of MODIS L1B data from Aqua and Terra further increased the number of available images for analysis (i.e. cases where ice could be seen under thin clouds).
Description of a water survey of Canada hydrometric stations on the Mackenzie River.
Scientific data set (SDS) and digital number (DN) values from MODIS L1B and L3 products used for the Mackenzie River.
Cloud cover presence was one of the few incidences where image processing was limited. This has also been previously reported (Riggs et al., 2000) where cloud cover in the Arctic limited data acquisition from the study site. This, in combination with coarse-resolution cloud cover masks resulted in 5–10 % of the images being omitted from analysis. Problems in snow detection arise when spectral characteristics important in the use of the normalised difference snow index (NDSI) make it difficult to discriminate between snow and specific cloud types (Hall et al., 2006). NDSI is insensitive to most clouds except when ice-containing clouds are present, exhibiting a similar spectral signature to snow. Hence, some MOD35/MYD35_L2 cloud mask images presented conservative over-masking of snow cover on cloudy and foggy days (Hall et al., 2006).
To improve temporal coverage, ice-off observations were also carried out at
varying overpass times (Chaouch et al., 2012) using MODIS L1B radiance
products from both Aqua and Terra satellites, which do not include the
MOD35/MYD35 cloud mask. During cloud-free conditions, L3 images were used to
sample data along sections of the river. Furthermore, to maximise the
availability of data collected, MODIS L1B was used when cloud cover was
present in L3 swaths. The MODIS snow product at 500 m spatial resolution
presents a cloud mask at 1 km spatial resolution. Using MODIS L1B enabled a
higher availability of recordable pixels at geographic locations, which were
cloud covered in the L3 images. It was concluded that more data pixels were
available to collect from MODIS L1B when cloud cover was present in L3
images. Image sets of DOYs 100–160 were analysed to observe patterns over the
entire ice break-up period ranging from 61 to 68
To avoid error in the SDS data collected, mixed pixels over the river consisting of water, ice and land were omitted. Furthermore, in sections of the river where pixel mixing was common as a result of smaller river widths, MODIS L1B was used. MODIS L1B with a spatial resolution of 250 m enabled to maximise data collection and minimise mixed pixel omission. The use of MODIS reflectance data at the 250 m spatial resolution (bands 1 and 2) has been compared to high-resolution Landsat for ice detection and produced a probability of detection at 91 % (Chaouch et al., 2012). Although it would be useful to compare Landsat high-resolution images to the current MODIS sample of observations, very few Landsat images were available with the targets dates and over the specific region where ice break-up was progressing to produce a comprehensive comparison. The combination of high cloud cover, high revisit cycles and rapid ice break-up processes (ranging from a few hours to a few days) limited the amount usable Landsat images.
In addition to determining instances of ice break-up events with respect to
location and time, this study also explored the use of MODIS as a tool for
estimating velocity of ice flows. Ice velocity was observed and recorded on
stretches of ice debris (
Estimated ice-off dates as illustrated by the red circles for selected years (2002, 2005, 2007 and 2009) on the Mackenzie River. Terra observations were made throughout the study period, while Aqua observations were available 2003–onward. Black circles are indicative of WSC ice observation dates.
Compilation of all ice-off dates from 2001 to 2013 DOY (day of year)
on the Mackenzie River. First ice break-up dates generally began near
325
Average ice break-up dates estimated from MODIS (2001–2013) are
given by the black dots, with
Time periods of observations and number of MODIS L3 and L1B images analysed during break-up on the Mackenzie River (2001–2013).
Over the 13 years of analysis, the ice break-up period ranged from as early
as DOY 115 and lasted as late as DOY 155. Most ice break-up over the 13-year
period (2001–2013) began between DOYs 115 and 125 and ended between DOYs 145
and 155. River morphology acted as an important spatial control determining
the type of ice break-up process and ice run. Ice break-up processes between
years showed different overall patterns with respect to location, and thus
temporally the beginning, end and duration of ice break-up varied. For
example, the initiation of ice break-up in 2002 (Fort Simpson,
330
The initiation of the ice break-up period on the Mackenzie River was
generally observed at the Liard River (325
As ice break-up proceeded northbound from the MR–Liard confluence, dynamic
ice break-up flushed the ice downstream in a shorter period of time than the
thermodynamic ice break-up south of the confluence (Figs. 3, 4). Generally,
however, distances above 560
Between 350 and 682
This example illustrates ice break-up at the headwaters of the Mackenzie River system in 2005 from DOYs 120 to 125.
Downstream of 682
Based on MODIS imagery, ice break-up began on average between DOYs 115 and 125
and ended between DOYs 145 and 155 (Fig. 5). The standard deviation of
estimated ice-off dates decreased with increasing latitude. MODIS-derived
dates showed highest deviations across river sections where thermodynamic ice
break-up was prevalent. These patterns are similar to those seen from average
break-up and standard deviations observed from the WSC. The 13-year average
reveals similar ice conditions in the low, mid- and high latitudes of the
Mackenzie River from MODIS and WSC data. There was an observed difference of
5 days between ice break-up observed from MODIS imagery and WSC. Also, the
respective standard deviations overlap across the similar periods. Ice
break-up in general continued in a north to south direction over the ice
break-up periods. Near Forth Simpson (330
In order to assess the relative timing of ice disappearance in relation to its surrounding sub-basin, the timing of river-ice disappearance was qualitatively compared to the timing of near complete snow disappearance from the surrounding area. MODIS L3 imagery of different years was selected which clearly revealed ice–snow relation with respect to location, where cloud cover was a minimal issue.
Locations where thermodynamic ice disappearance was hypothesised (south of
61.8
Change in channel width along the Mackenzie River as observed in
At reaches north of the MR–Liard River confluence, ice break-up and snowmelt were observed to initiate in sync with one another. As seen in Fig. 9, on DOYs 136–137/2011, ice disappearance on the southern cross-section of the figure is marked by the near simultaneous disappearance of snow. In fact by DOY 140/2011 both ice and snow had completely disappeared analogous to each other. On sections of the Mackenzie River before it enters the Mackenzie Delta, estimated ice break-up and snow disappearance was again observed to occur almost simultaneously (Fig. 12). Over a 6-day period (DOYs 137–142/2007) the ice break-up process continued until ice completely disappeared from the channel (MR). This process ensued sooner relative to complete snowmelt over the surrounding sub-basins. By DOY 142/2007 nearly one-third of the river was completely cleared of ice while most of the snow was still present over the MRB.
Principally, it was concluded that on the upper Mackenzie Basin snow cleared
sooner than the initiation of ice break-up. In the mid-Mackenzie Basin
(375–860
Example of thermodynamic break-up, where ice within the river requires an extra 2–3 days to be cleared after snow has melted over the immediate drainage basin. This process was observed in 2006 between DOYs 121 and 126.
Figures 10 and 11 illustrate ice movement from which ice velocities could be
estimated over periods of 3–4 days following secondary channel constriction
at 66
In 2008, the open-water/ice boundary (leading edge) was recorded beginning on
DOY 143 (Fig. 10). The open-water/ice (northern edge of ice) and
ice/open-water (following edge) boundaries were both visible from DOY 144.
Finally, the ice/open-water boundary was last observed on DOY 145. The
average ice-run velocity between 1063 and 1210
Over the 13-year period, the average estimated ice break-up dates were found
to range from DOYs 115 to 155 between distances 60 and 1460
Summary of results from previous investigations and this study showing the beginning and end of the ice break-up period with respect to location and range and duration of period. Also shown are the sources of data used, years covered for analyses and corresponding references.
Snowmelt and ice run over the Mackenzie River basin in 2011 between the DOYs 137 and 140. There is a 2-day lag between the complete clearance of snow on land and the clearance of ice on the Mackenzie River.
Ice flushing event recorded in 2008 between DOYs 143 and 146.
Ice flushing event recorded in 2010 between DOYs 138 and 141. Here, on DOY 141, the ice movement is last recorded after exiting into the Mackenzie Delta.
Observation of dynamic break-up over a section of the Mackenzie River basin, showing concurrent ice break-up and snowmelt over 6 days. This was observed in 2007 between DOYs 137 and 142.
In the headwaters of the Mackenzie River, ice break-up initiates the earliest
between Mill Lake (120
Furthermore, at the Liard River confluence (325
Channel morphology is, therefore, a more important control on ice break-up
patterns than previously believed. Both Pavelsky and Smith (2004) and de Rham
et al. (2008a) alluded to the fact that channel morphology may exert
influences on the patterns of ice break-up. De Munck et al. (2011), through
the use of geospatial modelling on the Chaudière River identified that
channel islands, confluences and channel sinuosity predisposed the Chaudière
River to ice jamming events. In this study, it is determined that channel
constriction at 350–682
Ice jamming from channel width decreases gave rise to similar sequences of ice-off observations, which occurred in tandem at two different latitudes, north and south of the ice jam (as seen at the Ramparts). Ice jams are therefore favourable where morphological features impede downstream ice passage (Beltaos, 1997). These ice jams are caused by channel constriction resulting from mid-channel islands and narrow reaches (Terroux et al., 1981). Channel braiding, constriction and changes in slope have also been reported to be important factors influencing ice break-up and flow regimes (de Rham et al., 2008a). In the context of our study, it was found that channel constrictions and bends represented locations where ice runs were impeded. Hicks (2009) also reported that running ice may be stalled when geometric constraints such as tight bends, narrow sections and islands are present in rivers. In fact, it has been shown that ice debris flow drop to a velocity of 0 in the presence of flow depths near channels islands and bars (Kääb et al., 2013). Lastly, Kääb and Prowse (2011), using ALOS PRISM stereo imagery on the Mackenzie River determined that ice velocities decrease to 0 in the presence of bars.
The estimated ice-run events illustrated in Figs. 7 and 10 may have been
caused by ice jam releases (javes) initiated at the Ramparts (1078
Ice-run velocities are believed to be the highest where the ice is minimally
effected by channel morphology, unconnected from incoming tributaries, and
channel splitting which causes the formation of islands (Kääb et
al., 2013). Amongst the variety of
ice runs observed over 13 years, ice velocities could be quantified in 2008
and 2010. Over 3–4-day periods, average ice velocities were estimated to be
1.21
MODIS is shown to be a viable tool for estimating river-ice velocities. This study finds that in order to monitor ice cover the river width needs to at least 0.5–1 km wide. Furthermore, to quantify river-ice velocities, the river width needs to be at least 1 km wide. With respect to the MR, ice velocities were only quantifiable above the Ramparts. The presence of morphological controls and therefore river width shortening leading to impeded ice run prevented quantifying velocities, as leading river-ice demarcations were difficult to locate. However, it was possible to estimate the overall velocity by observing ice/open-water boundaries. Lastly, it was determined that in order to measure ice-run velocities without major disturbance with impeded flows with respect to river morphology, estimates with MODIS should be made north of the Ramparts. North of the Ramparts, river widths were generally observed to be largest with respect to other parts of the MR.
The aim of this study was to develop an approach to estimate ice break-up dates on the Mackenzie River over more than a decade using MODIS snow and radiance products. It was found that the initiation of ice break-up started on average DOYs 115–125 and ended DOYs 145–155 over the 13 years analysed. Thermal ice break-up was an important process driving ice break-up south of the Liard River. Conversely, north of the Liard, ice break-up was dynamically driven. The addition to discharge from the MR–Liard River confluence outlined a location where initial ice break-up began. Furthermore, MODIS images allowed for the identification of important factors controlling ice runs and ice break-up, including morphological controls such as channel bars, river meandering and channel constriction.
MODIS is currently the most promising tool for frequent monitoring of river-ice processes as ground-based stations along the Mackenzie River are continuously being closed. Operating aboard two satellites (Aqua and Terra), the MODIS sensor allows for multiple daily acquisitions simultaneously along extensive stretches of the MR. Furthermore, MODIS is proving to be a viable sensor for the monitoring of river ice as shown in this and other recent investigations (e.g. Chaouch et al., 2012). In this study, monitoring of ice break-up on the Mackenzie River with MODIS proved to be a robust approach when compared to WSC ground-based observations. MODIS observations also allowed for the analysis of basin level processes influencing ice break-up, including river morphology and snowmelt.
Finally, future research should focus on investigating river-ice processes using a combination of ground-based and satellite-based sensors, particularly for examining relations between river morphology, ice strength and discharge. Data from these complementary technologies would be valuable in the context of an early warning system for municipalities where river-ice break-up is an important spring event causing significant flood damage. Furthermore, a multi-sensor approach using both optical and synthetic aperture radar (SAR) data would be advantageous in order to monitor ice river processes and floods in near real time. Satellite data from recent and upcoming SAR (Sentinel-1 and RADARSAT Constellation) and optical (Sentinel-2 and Sentinel-3) satellite missions will make such monitoring possible in the near future.
This research was supported by a NSERC Discovery grant number 193583-2012 to C. Duguay. We are grateful for the helpful comments of Ross Brown and two anonymous reviewers. Edited by: R. Brown