2.1 Study Area
The hydrological model setup to simulate flows along the Saint John River extends across the Saint John River Basin. This basin is situated in northeastern North America (Fig. 1), covering more than 55,000 km2 across the United States and Canada. While a major portion of the basin is located in Canada (51% and 13% in the provinces of New Brunswick and Quebec, respectively), the remaining portion (36%) is situated in the State of Maine, USA (Kidd et al., 2011). The Saint John River is more than 700 km long, flows from northern Maine, USA to western New Brunswick, Canada, before draining into the Bay of Fundy at Saint John, Canada. The total elevation drop of the river is about 480 m (Beltaos et al., 2012).
The Saint John River basin has mixed humid continental and maritime climates (Kidd, Curry and Munkittrick, 2011). The average annual precipitation is measured to be 1100 mm, in which 30% is snowfall (Beltaos et al., 2012). The mean annual discharge is approximately 1100 m3/s with a peak flow condition in later spring. The soil type in the basin is dominated by “forest soil” - humo-ferric podzols and gray luvisols. The land cover mostly consists of forests (70%), with some patches of cropland (6%) and wetlands (6%). There are three large hydroelectric reservoirs in the basin, impounded by the Grand Falls, Beechwood and Mactaquac dams. Since there is currently no active hydrometric station in the main river channel downstream of Fredericton hence the outlet station for the hydrological model of the basin was taken to be at the Mactaquac Dam, which reduces the hydrological model domain area to 41,000 km2.
The hydraulic model domain extends from Fort Kent to Grand Falls, an approximate 94 km long river reach. This portion of the river is prone to ice jam formation during spring breakup due to its geomorphological settings. The reach from Fort Kent to Edmundston is relatively steep with a series of rapids. The strech from Edmundston to Grand Falls has a relatively milder slope, shallow riverbed, and many islands and sandbars that splits the main river channels into multiple sub-channels.
Some hydraulic gauge stations record daily river flows and water levels along the study site. The United States Geological Survey (USGS) operates the gauging stations at Dickey and Fort Kent, ECCC’s Water Survey of Canada operate the gauge at Edmundston and New Brunswick Power own the gauge at Grand Falls. The hydrological model is calibrated and validated using streamflow records from Dickey and Grand Falls. Since the hydraulic model was calibrated and validated using the water levels recorded at the Edmundston gauge station and the model simulates ice jam backwater level profiles, the model framework was developed to forecast the severity of ice jams downstream of Edmundston.
2.2 MESH hydrological model
MESH is a physically-based hydrological land-surface model from Environment and Climate Change Canada (ECCC) (Pietroniro et al., 2007) and has been widely used in different parts of Canada, from small to large catchments (Mengistu & Spence, 2016; Haghnegahdar et al., 2017; Yassin et al., 2017; Lindenschmidt et al., 2019; Budhathoki et al., 2020; Rokaya et al., 2020). MESH uses a grouped response unit (GRU) approach to capture basin heterogeneity. It has a grid-based modelling system which is composed of three major components (i) a vertical exchange of water within a grid cell between the land surface and the atmosphere (ii) the routing of lateral fluxes and (iii) the generation of surface and sub-surface runoff. MESH uses the Canadian Land Surface Scheme (CLASS) (Verseghy, 1991) for the vertical generation and exchange of lateral fluxes. WATROF (Soulis et al., 2000) and PDMROF (Mekonnen et al., 2014) are the two scheme used to account for lateral fluxes. The routing of surface and subsurface runoff is performed using WATROUTE (Kouwen, 2016).
2.3 Meteorological Input for MESH
MESH requires seven meteorological forcing inputs: precipitation, wind speed, air temperature, specific humidity, incoming longwave radiation, barometric pressure and incoming shortwave radiation. For model calibration and validation, all inputs except precipitation were taken from combined gridded datasets of Global Environmental Multiscale (GEM) model (Côté et al., 1998; Yeh et al., 2002) which is available at an hourly temporal resolution and at the spatial resolution of 15 km. The precipitation inputs were taken from the Canadian Precipitation Analysis (CaPA) (Mahfouf et al., 2007) datasets which are available at 6 hour time intervals at a spatial resolution of 10 km. CaPA is found to be a reliable precipitation product for the Canadian domain (Boluwade et al., 2018).
For streamflow forecasting, all the meteorological forcing data were retrieved from Global Deterministic Prediction System (GDPS). GDPS is an operational forecasting system, based on the GEM model from ECCC which provides deterministic predictions of atmospheric variables with a 10-day lead time (Bélair et al., 2009; Charron et al., 2012). The forecasts are produced two times a day (00 UTC and 12 UTC) at 3-hourly temporal resolution and has an approximate 25 km spatial resolution.
2.4 MESH set up and calibration
“The topographic data for SJRB were obtained from the hydrologically adjusted elevation of MERIT Hydro which is at a resolution of 3 arc-second resolution (~ 90 m at the equator) (http://hydro.iis.u-tokyo.ac.jp/~yamadai/MERIT_Hydro/) (Yamazaki et al., 2019).The landcover data were derived from the Commission for Environmental Cooperation (CEC) land cover database in 30 m resolution (http://www.cec.org/north-american-environmental-atlas/land-cover-2010-landsat-30m/). The vegetation parameters were obtained from literature (Kidd et al., 2011) and the CLASS manual (Verseghy, 2009) and the soil texture information was obtained from the Unified North American Soil Map (UNASM) (LIU et al., 2014) for different soil depths.” (Budhathoki et al., submitted). Six vertical soil profile layers of 10 cm, 35 cm, 120 cm, 260 cm, 310 cm and 410 cm were defined from the surface boundary in MESH. The model was built with a grid resolution of 0.125 deg. (approx. 10 km), resulting in 373 grid cells. Nine GRUs were created based on the landcover variability in the basin. The preprocessing of the spatial data was conducted using ECCC’s Green Kenue software (EnSim Hydrologic, 2014) to generate drainage networks and other topographically driven basin characteristics such as slope and channel length. The discharge data were retrieved from ECCC’s database HYDAT and the reservoir inflows and outflows were retrieved from the New Brunswick Power company.
The calibration was performed using parallel DDS algorithm in OSTRICH (Matott, 2005) with the Nash Sutcliffe Efficiency (NSE) as the objective function. The sensitive parameters were selected based on Haghnegahdar et al. (2017) and ten parameters of six dominant GRU’s were calibrated. The model was calibrated for the period 2002–2010 considering the first year (Oct 2002 - Oct 2003) as the model spin-up period. The validation was then performed using the subsequent six years (2011–2018).
2.5 Streamflow Forecast
Forecasting the basin’s streamflow involves a two-step process, first running the MESH model in hindcast mode, which saves the state variables until the previous day (yesterday) of the forecast period and then performing the flow forecast for the next 10 days (from today) with the saved state variables. It is important to save and update the basin state variables and hydrologic conditions everyday so that the initial hydrologic conditions for running the model are always accurate. Figure 2 shows the schematic view of the MESH operational forecasting setup for the SJRB.
In the hindcasting mode, the forcing data for precipitation were obtained from CaPA and other meteorological forcing data were retrieved from the GEM system. In the forecasting mode, all the meteorological forcing data were retrieved from the GDPS system. MESH was run at an hourly time step in the hindcasting mode and 3-hourly in the forecasting mode to match the temporal resolution of the meteorological data.
2.6 RIVICE hydraulic model
RIVICE is a one-dimensional hydrodynamic model that simulates various river ice phenomena, including the formations of frazil ice, border ice, solid ice covers and ice jams. RIVICE solves the Saint Venant equations for transient flows and water levels using an implicit finite difference scheme. A user usually calibrates the time steps and appropriate lengths of the simulation based on specific sites and purposes. Surveyed cross-sections are the primary inputs to set up the model structure along a river. Moreover, the model requires various hydraulic and river ice parameters and boundary condition inputs to simulate these processes. A conceptual diagram of ice jam simulations and their require variables is shown in Fig. 3. Some of these parameters and boundary conditions are user-defined or calibrated based on historical events along the model domain. Table I briefly describes all of the parameters and boundary conditions. For further details about the RIVICE the reader may refer to the online manual (http://giws.usask.ca/rivice/Manual/RIVICE_Manual_2013-01-11.pdf) and to Lindenschmidt (2017).
Table I Description of RIVICE parameters and boundary conditions
Inputs
|
Description
|
Units
|
Boundary Conditions
|
|
|
Q
|
Upstream river discharge
|
m3/s
|
W
|
Downstream water level
|
m a.s.l
|
Vice
|
Inflowing volume of ice
|
m3
|
x
|
Toe of the ice-jam location
|
none
|
Parameters
|
|
|
PC
|
Porosity of ice-cover
|
none
|
FT
|
Thickness of ice-cover
|
m
|
PS
|
Porosity of slush pans
|
none
|
ST
|
Thickness of slush pans
|
m
|
vdep
|
ice deposition velocity
|
m/s
|
ver
|
ice erosion velocity
|
m/s
|
nbed
|
Riverbed roughness
|
s/m⅓
|
n8m
|
ice roughness
|
s/m⅓
|
K1
|
Longitudinal to lateral force ratio
|
none
|
K2
|
longitudinal to vertical force ratio
|
none
|
h
|
Thickness of ice downstream of jam
|
m
|
2.7 Stochastic framework for forecasting
In the stochastic framework (Fig. 4), the RIVICE hydrodynamic model is placed within a Monte-Carlo Analysis (MOCA) framework to simulate hundreds of ice jam scenarios using randomly selected sets of parameters and boundary conditions. To select random values of the parameters and boundary conditions, minimum and maximum values of the inputs were extracted from gauge records and the calibration data of previous studies along the model domain. While the uniform distribution of most of the parameters and toe of ice jam location are used to select the random values for the MOCA, an extreme value distribution (Gumbel) was implemented for two important boundary conditions – river discharge and the inflowing volume of ice.
An extreme value distribution was developed for river discharge using observed flows recorded at the Fort Kent gauging station during spring breakup. The location and scale parameters of the distribution were then used to select the random values from the maximum and minimum range of forecasted flows. The 3-day probable streamflow data from the MESH hydrological model was used to select the maximum and minimum range of the flows. The lateral flow inputs from various major tributaries along the model domain were also estimated by establishing linear relationships between the Fort Kent discharge and tributary flows.
The observed flow frequency distribution during spring breakup was used as an input in the MOCA framework. The volume-of-ice frequency distribution was then calibrated by comparing (i) the frequency distribution of the ensemble of stages simulated at Edmundston and (ii) the frequency distribution of the water level elevations recorded at the Edmundston gauge during ice-jam events. If the two distributions did not coincide, the volume-of-ice frequency distribution was adjusted and the MOCA repeated to yield a new “simulated” frequency distribution of stages at Edmundston for comparison, again, with the “observed” frequency distribution of the water level elevations recorded at Edmundston. The process is repeated until the “simulated” and “observed” frequency distributions of the volume of ice consistently coincided. A more detailed description of this process can be obtained from Lindenschmidt (2020; p. 181–183).
Once all the parameters and boundary conditions distributions were established, the framework was used to produce a seasonal outlook (before the breakup initiation along the model domain) of the severity of ice jam from 22 March 2021. The 3-day forecasting simulation began on 24 March 2021. Additional information was updated using the New Brunswick government’s daily interactive map of ice observation, especially important to track the toe of ice jam location.