«Pipeline Associated Watercourse Crossings 3rd Edition October 2005 The Canadian Association of Petroleum Producers (CAPP) is the voice of the ...»
A variety of site-specific and watershed management techniques are available to restore or enhance riparian and bank areas. Site-specific techniques are summarized in Table 6.1; appropriate Drawings are also referenced. Proponents should consult with technical specialists and public representatives to identify appropriate watershed restoration and enhancement procedures such as riparian fencing or public awareness.
At typical watercourse crossings where the banks are graded to a low angle, nearshore rearing and holding habitat is limited following completion of construction. Natural materials such as boulders (riprap and rock armouring), root balls and trees placed or anchored on streambanks can enhance nearshore habitat by providing hiding and resting places for juvenile and adult fish. The objectives of these methods are to provide economical, short- to long-term bank stabilization structures with a natural appearance and relatively low maintenance requirements.
Methods that increase the angle of the bank can also be installed. These include:
fibre and grass rolls; logwalls and cribwalls; overhangs and lunker structures;
brush layering, matting and bundles; tree revetments; and shrub planting and transplants. The objectives of these methods are to increase nearshore depth and encourage development of self-sustaining, overhanging plant cover. Many of these structures have a limited life span, so they should be designed to encourage natural bank development. Biodegradable products should be used whenever possible.
6.2.2 Instream Habitat Restoration and Enhancement The key characteristic of productive instream habitat is diversity. When properly used, instream structures and techniques can restore or enhance important or critical features such as spawning and food producing areas, cover and overwintering habitat. Spawning areas must provide a suitable environment during the egg laying, incubation and fry emergence periods. Food producing areas have substrate, depth and flow conditions that support aquatic invertebrates and forage fish. Instream cover provides fish protection from high current velocities and predators. Overhanging vegetation, undercut banks, submerged objects, depth and water turbulence provides cover (Wesche 1985).
A variety of site-specific and watershed management techniques are available to restore or enhance instream habitat. A general discussion of site-specific instream restoration and enhancement techniques is provided below. Additional information is summarized in Table 6.2 and Drawings are provided in Appendix A. Note that care must be taken to select suitable techniques, particularly for instream enhancement. Experience has shown that installation of ‘enhancement’ features that do not adequately reflect natural waterbody hydrology or ecology can create unwanted and undesirable long-term effects.
Removal of permanent obstructions to fish passage is an effective technique used to compensate for HADD. Instream barriers and debris can be natural (beaver dams, rocks, woody debris, falls) or man-made (garbage, culverts). Removal of barriers to fish movement can restore watershed connectivity by providing access to suitable spawning and rearing areas. Instream debris and barriers can slow stream flow, causing sediment deposition, increased water temperature and erosion where the debris redirects stream flow. Since natural barriers and debris also provide cover and overwintering habitats, technical specialists should be involved to determine whether these structures are beneficial or damaging habitat.
Care should also be taken to ensure that removal of barriers or debris does not result in unintended effects on downstream habitat.
Current deflectors can be constructed of logs, rocks, boulders, gabions or various combinations of these materials. These structures are typically angled downstream and include triangular and peninsular shapes (wing deflectors and groynes, respectively). Structure height is generally determined from low flow conditions.
Double-wing deflectors combining two current deflectors on opposite banks can also be used in larger streams to narrow the channel.
Low profile dams and weirs are multipurpose structures created from a variety of materials. Overpour structures are used to create pool habitat, raise water levels and collect and hold spawning gravel. They are most often used on small, high gradient streams and are relatively inexpensive, although construction is labour intensive. Their success depends on proper siting and construction; technical specialists should be involved to ensure that unwanted effects do not occur.
Substrate manipulation can be used in both warm- and cold-water habitats and includes placement or capture of suitable spawning materials and excavation of runs and pools. In streams with a natural bedload of granular spawning substrates, instream structures such as current deflectors, weirs and dams may be placed so that granular material is deposited and retained in suitable locations. Spreading clean gravel, especially when already used to construct dams for isolated watercourse crossings, can create spawning habitat if channel characteristics are appropriate. In streams with unstable flows or periodic flooding, catchment devices may be required to stabilize spawning substrates.
Proponents should consult with technical specialists and public representatives to identify appropriate watershed restoration and enhancement procedures. These include: road deactivation and rehabilitation; corridor fencing programs to protect waterbodies; sediment interception and retention; and public education programs to promote awareness of fisheries as well as fish habitat conservation and protection.
Instream structures have a limited life span and are susceptible to damage by floods and ice. A long-term monitoring and maintenance program should be initiated to maintain the integrity of restoration and enhancement projects and minimize unanticipated or unintended damage (Section 7.2). In addition, instream habitat restoration and enhancement may create an impediment to navigation.
Before any structures are installed, proponents should contact TC to ensure no concerns exist or the correct approvals are obtained.
Page 6-17 October 2005 Pipeline Associated Watercourse Crossings 3rd Edition 7 Monitoring Crossing Project Performance In sensitive watercourses, or where there is concern regarding impacts on fish or fish habitat, specific watercourse crossing objectives may be specified prior to construction. As discussed in Section 1.3, proponents are also advised to develop corporate or project-specific watercourse crossing objectives for inclusion in environmental protection plans, bid documents and regulatory applications. These crossing objectives may be based on existing legislation, fisheries management objectives for the area, or discussion with appropriate regulatory authorities and could include measurable water quality values or biophysical criteria or thresholds. Construction-related objectives could include duration, location or quantity of instream and riparian construction activities.
Objectives will depend on the watercourse being crossed, the species and habitat present and the time of construction. For example, protection of spawning and incubating habitat will be of primary importance for a crossing proposed during the spawning period. In this case, objectives could specify appropriate flow levels and suspended sediment concentrations, or maintenance of desirable substrate characteristics during the spawning and incubation period.
Section 35 of the Fisheries Act refers solely to fish habitat, but DFO’s Policy for the Management of Fish Habitat makes the link between habitat and productive capacity. Changes to productive capacity are not normally measured or estimated directly. Rather, the inferred change in productive capacity is based on an understanding of how physical, chemical and biological attributes describe habitat. Changes in these attributes are used as an indicator of changes in habitat and ultimately, productive capacity.
Once crossing objectives have been specified, construction inspection and monitoring and post-construction monitoring programs should be designed to evaluate crossing success (see Sections 7.1 and 7.2).
To identify opportunities where cost or risk can be minimized with no adverse biophysical effects, crossing success should be evaluated both after construction and after post-construction monitoring results are available. Ideally, all parties should be involved in these reviews, including: project managers; onsite inspection staff; environmental staff; contractors; technical specialists; and regulators.
7.1.1 Environmental Inspection Environmental inspection of construction at watercourse crossings by the proponent is recommended on all watercourses that are rated as having medium or high sensitivity. Inspection during construction on low sensitivity water crossings may be incorporated as part of the construction inspection.
Environmental inspection should be performed to ensure that the mitigation measures warranted at the crossings are implemented in a manner that minimizes the adverse environmental effects of construction. Environmental protection planning is of little value if the protection measures are ignored or poorly implemented during construction. It is critical that inspection start prior to the initial right-of-way preparation to prevent any mistakes early in the construction sequence. Environmental inspectors should have the appropriate authority to take corrective action as warranted including suspending an activity until the contractor complies with approvals or until approval from the appropriate government agency is obtained.
Inspectors should be chosen on the basis of their understanding of environmental requirements, knowledge of construction techniques and ultimately, their ability to integrate the two in the field and under pressure. Inspectors who cannot practically apply their environmental training or deal with the contractors will not likely last long on a construction spread. Inspectors who have little environmental training may not make the correct decision under pressure as they may not have the academic knowledge required to support their decisions. Finally, inspectors need capable contacts in the office that can research or support their decisions when they need assistance in making a decision while in the field.
7.1.2 Suspended Sediment Load Monitoring of suspended sediment load is the most common instream construction monitoring technique. This usually combines field monitoring of stream discharge and turbidity (a measure of transparency of the water column) with laboratory analysis of TSS and settleable solids concentrations. An empirical turbidity-TSS relationship is then derived, so that turbidity measurements can be used as an indicator of actual TSS and settleable solids levels (see Anderson et al.
1996). The presence of critical habitats may justify inclusion of additional sample sites, transects or other water quality parameters.
Established quantitative water quality guidelines for TSS and turbidity (e.g., CCME 1999) are based on chronic exposure data and do not represent a realistic objective for short-term instream activities. This is because these long-term, low concentration standards may not be applicable to short-term high concentration events such as those associated with pipeline crossings. For this reason, some specialists have applied sediment-dose models to establish water quality objectives and evaluate actual effects. These models (e.g., Newcombe and MacDonald 1991; Shen and Julien 1993; Anderson et al. 1996) predict effects on fish based on the duration and concentration of the sediment event, rather than a pre-established TSS/turbidity threshold.
Suspended sediment load monitoring should begin prior to construction and continue until water quality returns to control conditions and there is no potential for additional sediment plumes. Sampling immediately downstream of the crossing site (typically 100 m, the initial dilution zone) is important to document maximum sediment loads in the area with the highest potential for adverse effects.