This section will split river crossing maintenance into three groups – instream and permanent, instream and temporary, and single span bridges.
For all structures, prepare a routine maintenance plan which includes heavy rainfall response measures. Heavy rain and especially storms are likely to trigger maintenance. The main causes for maintenance are woody debris and scouring of inlets, outlets and abutments.
Check all new structures after heavy rain and flood flows. Instream structures often initially require regular maintenance. Fix any issues promptly. Take care cleaning sediment and woody debris around river crossings. In some situations, consider removing debris by hand rather than using heavy equipment, which can easily damage structures like culvert inlets.
The NES-PF has many regulations for river crossings that include maintenance. It is essential to understand these before starting maintenance. Consents may be required.
Consider fish passage retrofits, if necessary. Design and construction practices for fish passage through crossings has been discussed in Chapter 8: River crossings. This includes retrofitting options for non-fish accessible structures.
If there has been damage to a crossing’s structural integrity, seek professional expertise to fix it if there is no in-house expertise, or regulations require mitigation works to be signed off by an engineer.
9.10.1 Culverts, battery culverts, drift decks and fords
Check all instream structures for scouring around the inlets, batters and outlets, especially in culverts. This is due to water being forced to flow through a reduced opening. With the other structures, flood flows are designed to overtop the structures. With these, they can still scour or block as flow velocity still increases around the pipe edges as water is forced into the opening. The main cause of scour is damage caused by debris. Wing walls, aprons, cut-off walls and embankment paving can prevent scouring. If a structure has ongoing debris maintenance problems, consider constructing a debris control structure upstream to help prevent debris from even entering the culvert, battery culvert or drift deck.
Maintenance of structures typically includes:
- Removal of debris around and in the structure
- Re-enforcing the structures where there has been damage. For example, adding rock rip rap immediately downstream
- Maintenance of the approaching road grades, to eliminate water drainage along the road carriageway.
Culvert pipe inverts, the base of the pipe, and headwall and/or outlets wear out over time through debris and bed load abrasion or from water chemistry, especially corrugated steel. Concrete will have signs of cracking and rust protruding from reinforcing steel. Galvanised steel culverts may have severe rust, especially along joins, or the bottoms may have rotted or worn out. They should be repaired promptly to prevent further corrosion or structure collapse. Replacement may also be required. This often requires specialist engineering assistance. Culvert structural maintenance is beyond the scope of this Manual.
Check ford crossings after heavy rain or a flood flow event. Fords can create serious safety issues if the river bed has shifted, or there is river bed erosion affecting the ford’s concrete structure. Natural bed crossings are likely to need maintenance after most flood events, as riverbeds regularly change. This may include grading of the running surface, and addition of replacement of material, where necessary. Maintenance of fords must be completed with extreme care to minimise environmental effects especially when working with concrete or a river with a fine sediment substrate.
9.10.2 Temporary river crossing maintenance and removal
River crossings provide road access to a harvesting site, or give access for harvesting equipment where log extraction requires the need to temporarily cross a river. The maintenance of a temporary bridge is the same as that required for a permanent one, see 9.10.3 Single span bridges.
Poorly planned, constructed or maintained temporary harvest extraction river crossings provide one of the greatest opportunities for sediment delivery to water. They are also widely and regularly used by ground-based harvest machinery to extract felled trees. It is essential that temporary crossings are proactively managed, because river crossings can be difficult to maintain in wet periods, and the release of sediment at these times can be large if not managed well. Fix problems when they start to show rather than letting them turn into bigger ones. For example, approach tracks can rut out, so sediment can bypass control structures like cut-outs and directly enter the waterway. Getting machinery to try and fix the problem in poor conditions can lead to making the problem worse. Maintenance includes the following:
- Maintain the integrity of log crossings
- Maintain river crossings and approaches so that stormwater control is effective
- Ensure culverts are not getting blocked with woody debris from the harvest operation
- During wet weather, limit the use of the crossing to minimise mud accumulating on the track leading into and away from the crossing
- Stop operations when the approach tracks or the crossing are releasing sediment to the river, and divert any track stormwater onto the cut-over.
Ensure temporary crossings are removed. It is a NES-PF rule to remove the material used to construct the crossing within one week of finishing the operation. This can be done by the harvesting contractor, if they have suitable machinery like an excavator, immediately prior to shifting blocks. Otherwise, bring in suitable machinery to complete the work.
Crossing material should be placed in a location that minimises the risk of it entering the river; it needs to be shifted above the flood level. Make sure that additional logging slash built up due to using the crossing is also removed. Also, ensure that the approaches are rehabilitated or decommissioned to eliminate future sources of track sediment.
All material used to construct the instream crossing must be removed within one week of finishing the logging operation.
9.10.3 Single span bridges
Bridges need regular inspection and maintenance, depending on the type, age and level of use. It is recommended that permanent bridges have a regular two-year engineering inspection programme. WorkSafe’s Approved Code of Practice for Safety and Health in Forest Operations requires that ‘A bridge inspection programme shall be designed by a suitably experienced Chartered Professional Engineer’. Temporary bridges are structures that will not be in place for more than two years, but they should be inspected to make sure they continue to be fit for purpose.
The assessment should cover the condition of the material of each component, and how well each component is performing. This includes reviewing the condition of the bank protection measures, abutments, piers, bearers, beams, bracing, decking kerbs, rails and delineators, and signs. Repairs or replacement should be done where damaged or decayed members are located. If deterioration is severe, it may be necessary to limit the maximum vehicle weight on the bridge until repairs have been carried out.
It is good practice, when inspecting bridges, to have all previous information, such as photos, maps and previous inspection reports, at hand. It is also recommended that each inspection should take a minimum of 10 key photos so that they will form the maintenance record:
- Two photos of the elevation (side) view of the bridge, from upstream and downstream
- Two photos of the bridge deck and road surface, in both directions of travel
- Two photos of the underside of the bridge, taken from both ends of the bridge
- Four photos of the road embankment, adjacent to the abutments or wing walls
Refer Field Guide for Inspecting Bridges (FP innovations, 2011).
The specific maintenance will come out of the inspection. This could include stabilising bridge approaches to reduce rutting, cleaning bridge decks of gravel and debris, and fixing damaged rails. WorkSafe’s Approved Code of Practice for Safety and Health in Forest Operations requires all bridges with a load carrying capacity of less than Class 1 (7.1 tonne per axle) shall have their capacity signposted.
Many older bridges have lead-based paint. Always get professional advice and contact the regional council to make sure that removing old paint meets regulation. Sometimes a river channel may be subject to erosion next to and/or underneath an abutment. It may then be necessary to carry out river channel remedial work. Again, make sure you are familiar with the regulations including the NES-PF.