A field guide to oil spill response on freshwater shorelines: chapter 3

In freshwater environments, the shoreline zones are defined in relation to seasonal or annual water levels and swash zones (Table 3.1 and Figure 3.1).

Figure 3.1: River-stream cross-section

3.1 Lakes

Lake type nomenclature varies depending on the basis for classification, which may include temporal variation in water levels and volume, geologic origin or biological conditions.

Temporal (permanent/temporary)

Lake classifications may be based on seasonal variation in water levels and volume and include:

• Perennial: a lake that contains water throughout the year
• Ephemeral or Intermittent: a short-lived lake or pond which fills with water and dries up (i.e. disappears) seasonally
• Dry: an ephemeral lake that contains water only intermediately at irregular and infrequent intervals

Origin (geologic history)

Lake classification based on origin has traditionally included 11 major lake types: tectonic lakes, volcanic lakes, landslide lakes, glacial lakes, solution lakes, fluvial lakes, aeolian lakes, shoreline lakes, organic lakes, anthropomorphic lakes, and meteorite lakes (Hutchinson 1957). These can then be subdivided into more than 70 subtypes.

Trophic (biological productivity)

Lakes are commonly classified by their biological productivity or trophic level and range from oligotrophic (low productivity) to eutrophic (high productivity) with mesotrophic conditions in between (Figure 3.2).

Oligotrophic lakes generally contain low nutrient levels and thus low plant productivity allowing for abundant oxygen in deeper parts while eutrophic lakes are rich in nutrients and thus support high plant productivity. This high productivity in turn leads to increased decomposition rates and thus decreased oxygen levels at depth.

Figure 3.2: Lake trophic states

Considerations for the influence of different trophic levels on oiling include visibility, which decreases as productivity increases and sediment load, which increases as productivity increases. These in turn may have implications for detection and delineation and sediment loading of oil.

3.1.1 Swash zone shoreline types

The swash zone is that zone on a lake shoreline where oil is most likely to be stranded and where treatment would be conducted (Table 3.1). The substrates of the swash zone types that have been defined for this field guide are listed in Table 3.2 and described in Section 6.3.

On the Shoreline Cleanup Assessment Technique (SCAT) Lake Temperate Shoreline Oiling Summary (SOS) form (Section Shoreline Forms) the swash zone type is identified in box “4a. Shoreline type”.

Table 3.2: Swash zone shoreline types

Treatment approaches for different types of shoreline substrates are provided in Section 6.3.

3.1.2 Backshore geomorphology

In lacustrine or pond environments, the “Backshore” is above the limit of normal lake shore processes and is subject to inundation only during rare or catastrophic hydrological events (Table 3.1). Medium and long-term operational staging would be based in this backshore zone. Short-term staging can utilize the supra-swash zone bearing in mind that this zone may be rapidly inundated during an unpredictable high-water level event such as a storm surge or seiche (Section 3.1.3).

On the Lake Temperate SOS form the backshore character is identified in box “4b. BACKSHORE CHARACTER”.

3.1.3 Hydrodynamics

Significant differences between freshwater and marine environments in terms of water density, fetch, water levels and flow are introduced in Section 4.5. The following provides examples of these and other hydrodynamic characteristics of lakes.

Waves

Wave energy at the shoreline is a function of the fetch (the area over which the wind blows to generate waves), wind speed and wind duration. This energy can be generated by local winds or on distant parts of a large lake in the same manner as waves propagated on marine waters travel as swell towards a shoreline.

Water levels

Water levels on lakes vary in the long-term (annually or monthly and seasonal) and short-term (hours to weeks) depending on precipitation, seasonal snow and ice melting, and water storage in contributing rivers.

Long-term and seasonal change water levels

An example of the long-term annual average water levels for Lake Superior is provided in Figure 3.3, which shows a range of approx. 1.2 m. Within these long-term variations there is a seasonal (summer-winter) cycle that is illustrated in Figure 3.4, showing an approx. range of 0.9 m.

Figure 3.3: Long-term annual average water levels for Lake Superior, 1918-2018 (revised from US Army Corps of Engineers Detroit District)

Figure 3.4: Daily average water level variations in Lake Superior with the seasonal high and low envelopes (revised from US Army Corps of Engineers Detroit District)

Tides, seiches and storm surges

Tides occur on large lakes, such as the Great Lakes, but tidal water level changes are small (< 5 cm) and minor compared to other water-level fluctuations that result from winds and pressure changes.

Wind and weather conditions may create a seiche, which is an oscillating wave that can be a metre or greater in height. In many of the Great Lakes, the interval between the “high water” (i.e. set up) and “low water” (i.e. set down) of a seiche may be between four and seven hours. Figure 3.5 provides water level data for an approx. 3 m range seiche event measured on the north shore of Lake Erie with the primary oscillation in the early morning on 12 December 2000.

Wind-driven or “storm” surges which do not involve an oscillation are common, to a greater or lesser degree, on all lakes and ponds.

Figure 3.5: Water level data (in metres) measured at six gauging stations on the north shore of Lake Erie during a seiche event (Fisheries and Oceans Canada, Government of Canada)

Wind-driven or “storm” surges which do not involve an oscillation are common, to a greater or lesser degree, on all lakes and ponds.

Regulated water levels

Lake levels can be controlled by external (upstream) storage or release events on contributing rivers and streams or regulated by water control structures (e.g. dams, weirs). This ability to control water levels can buffer natural variations, but conversely can result in very large planned variations in the order of metres. On a larger geographic scale, water levels in the Great Lakes are regulated.

Ice

Ice may form on lake and pond waters anywhere in Canada as soon as air temperatures drop below freezing (Section 4.4.1). Ice can form in open waters, as shore fast ice, or as the growth of an ice foot, with the latter two forming earlier and persisting later in the season than on-water ice. These and other shoreline ice features (Section 4.4.2) may act to absorb or reflect waves. In winter months, the formation of these features may outweigh the role of waves as a factor in influencing oil movement and behaviour on lake shorelines.

An indication of the length of time each year that ice may form on a lake or lake shoreline can be gained from the average number of frost days (the number of days per year when the coldest temperature of the days is less than 0\xb0C), which ranges from > 300 days in the Arctic to < 100 days near the Great Lakes, Atlantic and Pacific coasts. For example, long-term data (1976-2005; Prairie Climate Centre, Climate Atlas) for Great Slave Lake (NT) show an average on the order of 250 “frost days” each year, whereas Cochrane (ON) and Okanagan Lake (BC) are on the order of 200 to 210 days. Figure 3.6 shows the variability between years on a comparable date (early March) in terms of total ice concentration (minimum, 2016; maximum, 2019) for the Great Lakes. The ice season in northern Lake Superior can be from December through late April, whereas eastern Lake Ontario typically has ice from January through early/mid-March.

Figure 3.6 A: Minimum total ice concentration, March 2016 for the Great Lakes (Meteorological Service of Canada, Environment and Climate Change Canada, Government of Canada)

Figure 3.6 B: Minimum total ice concentration, March 2016 (top panel) and maximum total ice concentration, March 2019 (bottom panel) for the Great Lakes (Meteorological Service of Canada, Environment and Climate Change Canada, Government of Canada)

3.2 Rivers and streams

The three primary river channel types at the most generalized level are based on the dominant substrate type of the system:

• bedrock, which is composed almost entirely of exposed rock
• alluvial or unconsolidated, which have a coating of sediment of varying thickness above existing bedrock
• man-made, which can be comprised of either solid or permeable substrates

3.2.1 Active channel margin shoreline types

The active channel margin type is the waterline, which varies within the active channel (Figure 3.1). The waterline varies through time (Section 3.2.4) and is the zone of river or stream bank where oil is most likely to be stranded and where treatment would be conducted (Table 3.1).

Within the generalized classification described above, there exist several more specific Active Channel Margin Types. The substrates of the Active Channel Margin Types that have been defined for this field guide are listed in Table 3.3 and described in Section 6.3. These can be found on the River (SOS) form and Stream (SOS) form in the box “4a. Shore type”.

Table 3.3: Active channel margin shoreline types

Treatment approaches for different types of shoreline substrates are provided in Section 6.3.

3.2.2 Character

River character can be classified in several ways and, depending on the system, some or all these approaches may be appropriate. The most applicable approach for spill response purposes is to document and describe the character of the valley which is occupied by the river channel(s), as this is important with respect to access and staging, and the character of the channel itself within which the river or stream flows. On the River (SOS) form and Stream (SOS) form (Section Shoreline Forms) these characteristics are captured in the “4c. river character” and “4c. stream character” boxes by “valley form, “river/stream form”, and “channel form”. Documentation of physical features, such as width, water depth, the presence or absence of shoals or point bars and oxbows, and their substrates is important as these characteristics have direct implications for shoreline treatment response planning and operations. These features are defined in the first section of box “4c.” on each form.

Valley form

The character and shape of the valley form in which the channel(s) has developed is a primary feature in terms of response planning and operations. The Shoreline Forms classify “Valley Form” as either Canyon, Confined or Leveed Channel or Flood Plain Valley:

• Canyon: A deeply incised, steep-sided river valley typically dominated by bedrock.
• Confined or leveed channel: A narrow, constricted system with vegetated or unconsolidated banks either naturally occurring or man-made.
• Flood plain valley: A broad, flat-floored valley which may be subject to seasonal or periodic inundation.

Channel form

Following the generalized river or stream and valley form characterizations, several more specific river channel forms/types are categorized as either small or intermediate, high gradient (> 2% change in elevation) channels or large, low gradient (< 2% change in elevation) channels.

These classifications can be further subdivided and may result from variations in substrate type, sediment loads and/or riparian vegetation types and amounts. Within these landscape level channel types, specific local level channel patterns such as oxbows and point bars may form based on similar factors as those that influence channel type.

Small or intermediate channel/high gradient

Small or intermediate, high gradient (> 2%) river and stream channels may display one or more channel types or forms including cascades, rapids, pools, riffles, glides or jams (Table 3.4, Figure 3.7). Development of these forms/types can depend on gradient and/or vegetation of the riparian zone and sediment or substrate.

Figure 3.7: Select high gradient channel forms: clockwise from top left – pool, straight glide, riffle, rapids (from ECCC 2012)

Large channel/low gradient

Large, low gradient (< 2%) river and stream channels can be divided into straight, meandering (single thread sinuous), anastomosing, braided and wandering forms or types (Table 3.5, Figure 3.8). Development of these forms/types can depend on gradient, vegetation of the riparian zone and sediment or substrate.

Figure 3.8: Large low gradient channel forms/types

3.2.3 Backshore geomorphology

In riverine environments, the “Backshore” is above the limit of normal channel processes, is subject to inundation only during rare or catastrophic hydrological events and is defined as the terraces and uplands above the “active floodplain” (Table 3.1 and Figure 3.1). Medium- and long-term operational staging would be based in this backshore zone. Short-term staging can utilize the floodplain (i.e. suprachannel) bearing in mind that this zone may be inundated rapidly during high-water levels, such as an unforeseen precipitation or “flash flood” event in upstream regions.

The character of the backshore is described in terms of the valley and channel forms and types (Section 3.2.2). On the River and Stream SOS forms, the backshore type is identified in box “4b. Overbank/ backshore type”.

3.2.4 Hydrodynamics

Rivers are dynamic and highly variable environments with respect to currents and water levels. The most significant feature of rivers, streams and creeks is that, for the most part, the flow is one direction. Wave action is typically not a significant hydrodynamic factor but wakes from large vessels and small boat traffic can cause wave heights of 1 m or greater at the active channel margin. Winds may be important with respect to oil transport as they can drive a slick against one bank and keep a lee-shore oil free.

Currents and flow

River, stream, and creek discharge vary constantly in response to changing inputs to the drainage system from precipitation, storm runoff, groundwater and snow/ice melt in the local and upstream areas. Flow direction and velocity typically vary locally, and back eddies or whirlpools are common as a river or steam channel varies in width and/ or depth and in the vicinity of shoals, bars, and islands (Figure 7.1.2).

The currents generated by river discharge are the dominant factor in oil dispersal and transport. Current speeds are lower at the banks and the bottom (due to friction) so that water moves faster at the surface in the centre of a channel. This causes oil to spread rapidly and there may be considerable mixing behind the leading edge of an oil plume. Flow, and therefore current speed, increase as the channel cross-sectional area decreases and decrease as a channel widens and/or deepens.

Importantly, turbulent mixing occurs throughout the water column, even in large rivers, so that floating oil is entrained throughout the water column. Two significant effects of this entrainment may be:

• contact of the oil with bottom sediments and a resulting increase in the density of the oil-sediment mixture (Section 7.3)
• to make detection of subsurface oil considerably more difficult and result in underestimates of oil distributions and volumes

Figure 3.9 illustrates relatively little seasonal variability but three significant discharge events during which current velocities were observed to significantly and rapidly increase.

Figure 3.9: Observed discharge for the North Saskatchewan River near Deer Creek (AB), 2016 (Water Office, Government of Canada)

Water levels

Water levels vary constantly in response to changing discharge volumes and can result from ice jams (Section Ice). Two critical effects of changing water levels are that the substrate character (Section 3.2.1) and the channel morphology (Section 3.2.2) typically change with rising or falling water levels. A channel that may be navigable at one water level may not be at a lower level. Similarly, a submerged sand shoal may be exposed as a sandy bar or island at low water levels and at higher water levels oil could be stranded on the suprachannel zone or floodplain vegetation (Section 7.1.1). For discharges in Figure 3.9, the corresponding water levels varied over a 3 m range.

Seasonal change

Seasonal water level changes result from a combination of precipitation, storm runoff, groundwater and snow/ice melt in the local and upstream drainage basin. A typical feature of rivers in much of Canada is the increase in water levels during the spring high run-off period (“freshet”) due to the thaw of snow and ice. Frequently the freshet inundates the active floodplain zone (Figure 3.1).

Event-related changes

The late July high discharge/water level event illustrated in Figure 3.9 occurred during an incidental oil release from the land into the river and resulted in oil stranding on the river banks during a period of a falling water levels (Figure 7.1, bottom panel). The late August high discharge/water level event resulted in oil burial (Section 7.2) in river sections and a redistribution of stranded oil and oiled woody material (Section 7.1.3) farther downstream. Other examples of oiling during periods of high water-level events are provided in Section 7.1.1.

Tidal influence

Tidal influence may occur on coastal rivers [e.g. Fraser River (BC), St. Lawrence River (QC), and Saint John River (NB)] for some distance upstream from their confluence with the marine environment. These rivers experience tidal-related water level changes and water flow direction reversals with corresponding water velocity fluctuations daily. For example, daily tidal-related water level changes on the Pitt River (BC) may be over 1 m depending on the time of year (Figure 3.10).

Figure 3.10: August 2018 record for the Pitt River near Port Coquitlam (BC) illustrating diurnal changes in water level due to tidal influence (Water Office, Government of Canada)

Regulated water levels

Many rivers are regulated by dams and weirs to adjust downstream discharge and water levels. For example, the 146,300 km² of drainage basin and 1,130 km of river length in the Ottawa River Basin have 13 control structures primarily to store water in reservoirs for release to augment low flow conditions and for flood control during the spring freshet. Figure 3.11 illustrates daily changes in river water level (green line) on the order of 25 cm due to regulation at a hydroelectric generating station (i.e. dam) on the North Saskatchewan River.

Figure 3.11: Two-week record for the North Saskatchewan River near Rocky Mountain House (AB) illustrating diurnal changes in water levels due to water releases from the Big Horn Dam, October 2018 (Water Office, Government of Canada)

Ice

Ice formation and shoreline ice features in rivers and streams are similar to those for lake and pond waters (Section 3.1.3). Ice jams that form during break-up are a common feature of rivers in Canada (Figure 3.12) and frequently lead to ice jam floods.

Figure 3.12: Ice jam under bridge at Acadie River (Environment and Climate Change Canada, 2021)

Ice may form on rivers, creeks, and streams anywhere in Canada. An indication of the length of time each year that ice may form on a river, creek or stream can be gained from the average number of frost days (the number of days per year when the coldest temperature of the days is less than 0\u02daC), which ranges from > 300 days in the Arctic to < 100 days near the Great Lakes, Atlantic and Pacific coasts. For example, long-term data (1976-2005) for Inuvik (NT) on the Mackenzie River show an average on the order of 260 “frost days” each year, whereas Fort Simpson (NT) at the confluence of the Mackenzie and Laird Rivers in the southern portion of the drainage basin has 220, the North Saskatchewan River near Saskatoon (SK) has 200, and the lower Ottawa River (ON) has on the order of 165 days (Prairie Climate Centre, Climate Atlas). On large rivers, freeze-up and break-up vary with location. As an example, on the Mackenzie River:

• ice begins to break up in early to mid-May in the southern sections of the river, after break-up on the Liard River (tributary rivers typically are free of ice before the Mackenzie itself)
• high water levels and flooding are common during the break-up period, particularly when ice dams form
• break-up across the lower Mackenzie River typically occurs late May and the channels in the delta are usually free of floating river ice by the end of May or early June