A field guide to oil spill response on freshwater shorelines: chapter 7

7.1 Rivers

7.1.1 Water levels and oil

River, stream, and creek water levels vary constantly in response to changing inputs to the drainage system from precipitation, storm runoff, groundwater and snow/ice melt (Section 3.2.4). These variations may be small and ephemeral, only changing the water level by some tens of centimetres for a few hours to overbank flooding of several metres that may persist for days to weeks. Oil stranded on a falling water level may coat the river bank (Figure 7.1). Oil stranded during a flood event may be deposited on a flood plain above the active channel (Figure 7.1) and effectively become a land spill unaffected by water action for some months thereafter (Figure 7.2).

Figure 7.1: Oil (weathered crude – left panel; unweathered heavy crude – right panel) stranded during a falling water level

Figure 7.2: Oil deposited on a flood plain during a flood event

The effect on oil already stranded on the river bank is a function of whether the water level rises or falls and can result in either removal or burial of the previously stranded oil. Stranded oil that is removed may be transported and redeposited downstream.

7.1.2 Response in fast water

The term “Fast water” or “Fast current” when describing spill response refers generally to oil spills in water moving at one knot (0.5 m/s) or greater.

Responding to spills in fast water environments imposes additional hazards due to the extreme loads placed on equipment and the danger of personnel being swept away in fast currents. Safety of responders must always be assessed before attempting to deploy equipment in fast water. The use of boom as a floating barrier is subject to failure for a variety of reasons (Figure 7.3). Boom failure tends to occur when the current speed exceeds 0.75 knots (0.4 m/s). Depending on the issue, boom failure may be corrected by changing the boom angle, boom length, boom size (e.g. skirt length) or anchor weight. It is also possible that booming operations are not feasible in certain locations and a new spill management location must be used. Booming strategies are generally well understood by field responders; however, in fast water or in ice, there are additional considerations.

Figure 7.3: Typical boom failures often caused by fast current speed

As the current speed increases, the force on the boom and its components also increases. It is possible to reduce these forces by using boom with a shorter skirt, changing the boom angle in relation to the shoreline, and/or by reducing the length of the boom sections. If current speed is less than 2 knots, a boom skirt length of 12 inches (approx. 30 cm) is appropriate; however, as current speed increases to greater than 2 knots, a skirt length of 6 inches (approx. 15 cm) or shorter is recommended. Table 7.1 depicts the river speed and the recommended boom angle and length for river boom. These are approximations and adjustments in the field would be required. The reduction in boom length and boom angle may necessitate the use of cascade booming in order to cover the area required for deflection booming operations. Shorter sections of boom are used and anchored in an overlapping pattern to direct oil towards a collection area. Chevron booming configurations may also be used in fast water (Section 6.2.1). The use of BoomVanes^TM or specialized sweep/buster systems may also be considered for larger rivers or bodies of water. These units can operate effectively in much faster currents (i.e. 3 knots for smaller systems and up to 5 knots for larger systems) but require a minimum depth of water.

In fast water where shorter boom sections are necessary, there is a requirement for additional anchor systems. Multiple anchors, lines and buoys add to the complexity of the deployment and increase the chances of lines fouling or becoming entangled in propellers. Responders need to review the plan for anchoring and approach it systematically to avoid these issues. The use of trip lines will help when removing anchors, especially in fast water where the additional force may cause anchors to be set deeply and are therefore difficult to pull out of the bottom sediments. The use of shoreline anchors and cable ferry systems require good, secure anchor points. Shoreline anchor plates help to spread the load over several anchor points. Lines under tension are a safety issue and responders must be aware of the risk and avoid positioning themselves in the ‘snap-back zone’ (i.e. the direct path of a parting line).

When planning response strategies in fast water environments it is critical to understand and characterize the operating environment, including such factors as currents and flow patterns, natural collection sites, and then translating the information into estimating current and deflection angles, and potential forces on boom and rigging (Figure 7.4). For example, the selection of a booming strategy and technique should involve an understanding of the nature of current flow and the variations in speed between the faster-flowing cut-bank areas and the generally slower-moving, more quiescent areas along the inner bends in a river or stream (Figure 7.5). Current speeds increase as channels narrow and turbulence or eddies are common in the lee of shoals or islands and at a confluence.

Figure 7.4: Typical river flow patterns and boom deployments

Figure 7.5: Example of booming strategy in a channel

7.1.3 Small and large woody material

Woody material is a common feature of rivers and streams in Canada. The origin of the material may be natural river bank erosion, upstream transport or beaver cutting and the woody deposits may occur as lines of debris at a former or current water level, log jams and beaver lodges or dams (Figure 7.6). Large woody material (LWM) is defined as an unconsolidated accumulation of material larger than 10 cm in diameter and small woody material (SWM) as similar accumulations less than 10 cm in diameter.

Figure 7.6: Line of woody material stranded at former high-water level

Debris lines or log jams typically are ephemeral features that are created by and reconfigured or removed by high water level events associated with period of high discharge, such as a spring freshet. Beaver activity sites with LWM may be defined as active or inactive lodges, feed piles, embankment dens, or dams (Figure 7.7).

Figure 7.7: Beaver activity site: feed pile

Treatment approaches for small and large woody material are described in Section 6.3.1, Freshwater Substrate Information Sheet #13.

7.2 Subsurface oil on sediment beaches, banks or bars

7.2.1 Introduction

Stranded oil can penetrate sediments or be buried by wave and current action (Figure 7.8).

Figure 7.8: Oil stranding on shoreline

Penetration is controlled by the oil character and the sediment size – the potential for penetration decreases with viscosity and sediment grain size (Figure 7.9). Burial is the result of sediment transport and deposition by water flowing over the stranded oil (Figure 7.10).

Figure 7.9: Cobble beach on which emulsified oil has penetrated > 1 m before reaching an impermeable hard sand layer

Figure 7.10: Oiled debris and sediments located approx. 5-10 cm below the sediment surface

7.2.2 Detection and delineation

The current practice for detection and delineation of subsurface oil in sediment shorelines relies primarily on the use of manually or mechanically excavated pits and trenches to allow visual examination and documentation of subsurface conditions and/or sampling for offsite analysis. Table 7.2 summarizes existing accepted practices in terms of horizontal detection and delineation, vertical delineation, survey speed, oil character and relative cost.

Visual examination in pits and trenches, when used with a systematic SCAT documentation program has generally been adequate to meet operational needs. However, these procedures are typically labour intensive, excessively time consuming, and are limited in their ability to accurately and efficiently delineate the three-dimensional extent of subsurface oiling, particularly in the horizontal dimension. This limitation is largely because the excavations rely on discontinuous, or spot, samples which are collected either randomly or on fixed sampling grids. The accuracy of delineations using excavations can be improved through collection of additional samples, but only with additional expenditures of time and resources. Even with an intensive excavation survey, pitting and trenching may only cover a small percentage (< 0.1%) of the subsurface area. To a large degree, the selection of sample locations is based on the interpretation, by an experienced coastal geomorphologist or sedimentologist, of shoreline morphology and the recent history (typically days to weeks) of processes that cause erosion and deposition. This professional judgment does not guarantee that subsurface oil will be detected in the sample locations.

The speed and accuracy limitations of a pit or trench sampling survey can be overcome in some situations by oil detection canines (“detection dogs”; Section 7.4).

When a large number of pits are dug, the use of hand-held devices such as smart phones or tablets running any number of customizable data collection applications can be used to quickly collect spatial data, attribute information on oiling, and photographs of a large number of subsurface pits in a timelier manner. Relatively simple computer applications can document the pit observations efficiently, minimize paper transfers and provide a file for direct integration into a desktop GIS.

7.3 Submerged and sunken oil

Most oils have a density less than water and float in still-water conditions. Fresh water typically has a density of 1000 kg/m³ and oils that exceed that density may be submerged, temporarily or for lengthy time periods, or may sink to a lake or river bed. An oil that has a density less than fresh water may become denser due to weathering or emulsification or if it is mixed with macroscopic (>1 mm) shoreline, river bank or river bottom sediments (Section 4.1.6).

7.3.1 Definitions

Submerged oil

Oil below the surface of the water that is suspended within the water column (Figure 7.11). The primary controlling environmental factor is that of water movement:

• Oil that is neutrally or slightly positively buoyant may be temporarily submerged due to turbulence associated with wave action or currents and would float to the surface in the absence of that turbulence.
• Turbulent mixing on lakes and ponds typically is limited to the surface waters and is a function of the level of wave energy; essentially this is a two-dimensional process within the upper water layer.
• In rivers, streams and creeks, under energetic flow conditions turbulent mixing typically is throughout the water column, irrespective of water depth; essentially, a three-dimensional process.

Figure 7.11 Submerged and sunken oil

Sunken oil

Oil that is negatively buoyant deposited on the lake bed or river bed. Sunken oil may be reworked transported as bed load or buried (“subsurface sunken oil”). The primary sources and pathways for sunken oil include:

• Oil which is denser than the water body.
• Oil whose density has increased through weathering processes and becomes denser than the water body (this can include residues from in situ burning).
• Oil whose density has increased as a result of entrainment of macroscopic sediments (> 1 mm) so that the oil-sediment aggregate becomes denser than the water body (Section 4.1.6).
• Turbulence associated with wave action or currents may temporarily suspend sunken oil.
• Some sunken oil may be relatively fixed in position (immobile) and some may be very susceptible to movement and relocation due to slight changes in currents or even water temperatures (Figure 7.12).
• Sunken oil accumulations typically are very patchy in distribution.
• In some cases, lowering seasonal water levels may expose previously sunken oil, to a more readily accessible stranded oil form; or the opposite may occur, and oil may be inundated with increasing water levels.

Figure 7.12 Sunken oil in shallow, nearshore freshwater environments

7.3.2 Detection and delineation

Many challenges exist for the detection and delineation of submerged and sunken oil. The most common constraining factors include water depth, visibility, currents, and the mobility of oil in the water column, unless the environment is a still-water location. Submerged and sunken mats may be visible from the air, boats, shorelines, or by snorkel or diver teams.

A range of techniques are available to detect and delineate sunken oil. The operating environments and the advantages and limitations of currently available detection and delineation techniques for sunken oil (Table 7.3) are described in API 2016.

Operationally, detection, delineation and response techniques may be broadly divided into shallow water/shore-based options (Figure 7.13) versus those that are deeper water and boat-based.

Figure 7.13: Shallow water/shore-based options for sunken oil detection and delineation

7.3.3. Response options

Many challenges exist for the recovery of submerged oil of which the most constraining factor is the mobility of oil in the water column, unless the environment is a still-water location. The only practical options for submerged visible oil mats within the water column are vacuums/ pumps (depending on oil viscosity), trawls, nets, and sorbents.

A range of techniques are available to recover sunken oil (Figure 7.14). The operating environments and the advantages and limitations of currently available recovery techniques for sunken oil (Table 7.4) are described in API 2016. All dive activities in the vicinity of submerged or sunken must be conducted by commercial divers with appropriate PPE.

Figure 7.14: Sunken oil recovery options in shallow water with good visibility

7.4 Oil detection canines

Recent advances for the detection and delineation of both surface and subsurface oil on shorelines have resulted from controlled field trials and participation in oil spill response operations using trained oil detection canines (ODCs) and professional handlers. In particular, field trials have demonstrated that:

• Trained canine teams have the potential for accurate (> 99%) and rapid detection and horizontal delineation of subsurface oil.
• The survey speed for subsurface oil detection or area clearance is many times faster than can be achieved by walking or mobile SCAT teams.
• A team approach involves:
  • Trained and imprinted detection canine(s);
  • Certified professional handler(s);
  • A K9-SCAT Liaison (who has trained with canine detection teams).

The proven applications of ODCs to support shoreline oiling assessment surveys (K9 SCAT) are summarized in Table 7.5.

An ODC team can survey at track line speeds on the order of 3 to 6 km/hr on sand beaches and 2.5 to 4.5 km/hr on more difficult coarse-sediment beaches. These speeds equate to an equivalent alongshore subsurface detection coverage speed up to 2.4 km/hr on sand beaches and 200 to 500 m/hr on coarse-sediment beaches. Field trials showed that an ODC can locate subsurface oil and can achieve this detection and delineation with a better efficiency and greater accuracy (high confidence, low risk) compared to traditional manual or mechanical excavation based on spot samples (low confidence, high risk). This capability is particularly valuable for clearance surveys in which an ODC team can cover large areas rapidly with a high confidence of No Detectable Oil (NDO) (Figure 7.15), thus saving considerable amounts of time and effort and freeing experienced SCAT Team Leads to focus on oiled areas where treatment actions may be required.

Figure 7.15: Oil Detection Canine (ODC) team conducting search of wide mud flat with vegetation

7.5 Unmanned aerial systems (uASs)

Unmanned Aerial Systems (UASs) are a valuable tool with specific applications for shoreline surveys or in the broader context of an oil spill response, particularly for freshwater environments without pre-existing segmentation and/or video coverage (e.g. a large proportion of Canadian inland waterways).

Small UASs (sUASs; <25 kg) are a relatively easy-to-use, rapidly deployable, and practical local surveillance tool on oil spills for many over-water and over-land applications, including SCAT surveys on shorelines. In addition, advances in larger, longer endurance fixed-wing UAS vehicles offer the potential to perform extended Beyond Visual Line of Sight (BVLOS) surveys covering larger geographic regions than is feasible with sUAS, which offers the potential to replace typical missions performed by manned fixed-wing or helicopter platforms.

The most common, applicable and readily available platforms for conducting SCAT field surveys are summarized in Table 7.6.

There currently exist several options for shoreline survey methodology with sUASs. Similar to K9 SCAT surveys, these types of survey are unique in that a qualified SCAT person is needed as well as a trained professional to operate the UAS (or handler in the case of K9 surveys). Ideally these are not the same person thus allowing each to focus on their specific responsibilities. Most sUASs can be operated from a tablet atop the controller allowing the SCAT team lead to observe imagery mid-flight. This however can be difficult depending on the lighting conditions and may interfere with the pilot’s ability to safely operate the unit.

sUAS surveys are documented in much the same manner as traditional foot, boat or aircraft surveys. However, because of the variables involved an alternate, simplified oiling summary form is more practical. The Shoreline Oiling Aerial Reconnaissance (SOAR) form has been developed to meet the data capture needs of a sUAS shoreline survey. Although some components of the form are familiar to traditional SCAT there are modifications to the oiling Information section to streamline and simplify the capture of oiling data (Figure 7.16).

Figure 7.16: Shoreline oiling aerial reconnaissance (SOAR) form

For traditional shoreline surveys, sUASs could be considered as a replacement to foot- and boat-based surveys when access and/or safety are an issue. However, sUAS surveys do not provide the same level of detail as a foot inspection and this should be factored into the decision process. sUAS imagery can be very reliable for large area, bulk oiling situations or highly visible and contrasting visual oiling scenarios. However, sUASs will likely not suffice for final or sign-off inspections unless access or safety concerns are an issue.