[Community Watershed Guidebook Table of Contents]
There are two objectives for riparian management areas (RMAs) in community watersheds:
- to minimize the impacts of forest and range use on stream and lake water quality by providing a vegetated buffer and filter between those activities and the streams
- to maintain stream channel stability by protecting streambanks and streambank vegetation and by ensuring that a long-term supply of large wood is available for stream channel processes.
This section summarizes the regulations and guidelines for riparian management on community watershed streams. Consult the Riparian Management Area Guidebook for complete Forest Practices Code guidelines.
A stream is defined in the Forest Practices Code as…a watercourse having an alluvial sediment bed, formed when water flows on a perennial or intermittent basis between definable streambanks.
For the Forest Practices Code regulations and this guidebook, the above definition applies. This definition of a stream differs from that in the Water Act.
Small channels, particularly in the interior, may be difficult to classify as streams. The key is evidence of fluvial activity along most of the channel length. Fluvial activity is apparent from the formation of definable streambanks and a stream bed. The stream bed has gravel or sand, or if flowing over bedrock, areas where fine particles have been scoured. Streambanks are continual (i.e., constantly recurring) but may be discontinuous over short sections of the stream.
Man-made channels such as irrigation ditches or any other ditch are not considered streams. Where short sections of a natural stream have been diverted through a man-made channel, the entire stream should receive the same level of protection.
A perennial stream is defined in this guidebook as any stream where it is reasonably likely that the streamflows after July 15 in most years. Intermittent streams normally do not have summer flow after July 15. Ephemeral streams flow only during storms.
All streams and lakes in the area affected by a proposed forest development plan must be shown on the forest development plan map. All streams and lakes affected by a range plan must be shown on the range use plan map.
The Operational Planning Regulation requires that RMA boundaries be established for any forestry operation in a community watershed, including harvesting, road construction, maintenance or deactivation, and silvicultural activity. For range practices, however, RMA boundaries need not be established. Instead, all streams in the range use plan must be mapped, and riparian areas recognized around those streams based on vegetation boundaries (see Riparian Management Area Guidebook).
The RMA extends from the top of the streambank to:
- a slope distance specified in Table 7
- the top of the inner gorge
- the outer edge of the active floodplain
- the outer edge of any wetlands or ponds contiguous with the RMA, whichever is greatest.
Table 7 shows the minimum stream classes, reserve zones and management zone widths that apply to all community watershed streams.
Table 7. Stream classes and minimum riparian slope distances for riparian management areas
The values shown in Table 7 are the minimum widths for RMAs. Expert assessment of local topographic, channel and forest conditions, as indicated on air photos and from fieldwork, should be done to widen the RMA as required. This is to ensure that the areas are windfirm and take in unstable hill slopes and stream channels.
The regulations allow the Ministry of Forests district manager, with the agreement of the designated environment official, to narrow the width of the riparian reserve or management zone or to harvest within the reserve under certain specified conditions. The Riparian Management Area Guidebook lists the reasons that trees may be removed or altered within the riparian reserve.
The Riparian Management Area Guidebook has a detailed list of recommended management prescriptions for RMAs. Below are some additional prescriptions specific to community watersheds, which focus on protecting water quality.
In-stream work
- The water purveyor must be informed when in-stream construction activity will occur. The Road Engineering Regulation states that water licensees or their representatives and the designated environment official must be informed of the start date of road construction or modification at least 48 hours before the start of that activity. The purpose of the regulation is to allow water licensees to increase water quality monitoring if they desire (see section 5 "Water quality monitoring") or shift to an alternative water supply.
- Machinery should be operated from the streambank or, when in the stream, "in the dry" between impermeable dam structures made with the use of flumes, dam and pump methods, or silt fences.
- All temporary diversion channels or right-of-way ditches constructed of erodible material must be lined with appropriate material (e.g., plastic sheeting, filter cloth or clean gravel) to prevent siltation from channel erosion.
- The exterior of all machinery operating within the wet perimeter of the channel must be free of excessive lubricants.
- Machinery must not be refueled or lubricated within the RMA or the wet perimeter of the channel.
- Where an inadvertent leakage of fuel or lubricant occurs, the contaminated material must be removed and disposed of outside the community watershed. Inform the Environmental Protection Department, BC Environment of any leaks.
- Where a crossing site has to be dewatered, sediment release into the stream should be prevented by pumping affected water onto a stable vegetated area away from the stream or into a settling pond.
- If backfilling cribs with the original excavated material would cause excessive siltation, then clean, granular fill should be used instead.
Roads
- Roads are not permitted within a riparian reserve, except at designated stream crossings, unless a road elsewhere would result in an even higher risk of sediment reaching the creek. Obtain agreement from Ministry of Environment, Lands and Parks before constructing roads within an RMA beside a stream.
- Any road proposed in an RMA should have an engineering plan that specifies how sediment will be controlled.
- Any inactive roads within an RMA should be deactivated. Those on a floodplain should be permanently deactivated, as they are a significant hazard to channel stability. During floods, rivers flow down or along roadways.
- Extra and oversized culverts should be installed where roads cross floodplains.
Landings
- Landings must not be closer than 30 m to a stream. Landings should not be in a RMA unless there is no practical alternative and locating a landing elsewhere would create a higher risk of sediment delivery. Ensuring that the landing is at least 30 m away allows for the growth of the landing and provides sufficient buffer for sediment, ash and fuel spill infiltration.
- Where landings have to be located within 30 m of a stream, they should be less than 0.25 ha in area, and be designed to control runoff and sediment. Completely deactivate them immediately after use.
- Landing debris should not be pushed toward a stream. Debris should be placed on the high side of the landing and disposed of in a manner that minimizes impact on water quality.
S1, S2 and S3 streams
S4 streams
- If the community water intake is on an S4 stream, no harvesting should take place within 20 m of the channel for at least 1000 m above the intake.
- Along other S4 streams, enough stream-side trees must be retained in the management zone to maintain streambank stability and to prevent downstream impacts on water quality.
- The target conditions for S4 management zones differ for perennial and intermittent streams. Around all perennial streams at least 50 per cent (coast) or 100 per cent (interior) of windfirm coniferous trees, and all understorey and deciduous trees should be retained within 10 m of the channel.
- Along ephemeral streams, and around perennial streams with a moderate windthrow hazard, only deciduous and non-merchantable coniferous trees, need to be retained. Excessive windthrow of large trees on these sites could impact water quality through streambank damage.
- Machinery must be kept at least 5 m away from the streambank, and all understorey and non-merchantable vegetation must be retained within 5 m of the streambank.
- All slash and debris that enters a stream must be removed. Clean-out should be carefully monitored, however, to ensure that only unstable debris is removed and placed above the high water mark. Removal of stable debris is detrimental to channel stability. Refer to the Riparian Management Area Guidebook for details on stream clean-out procedures.
Gullies
- All gullies in community watersheds with stream channels greater than 1.5 m wide must have 20 m riparian reserves.
- On the coast, harvesting should not occur in gullies with a high debris flow or transport hazard.
- On the coast, any harvesting within the management zones of gullies must follow the recommended prescriptions of the Gully Assessment Procedure Guidebook.
- Deciduous trees are not an acceptable substitute for original stand conifers. Extensive areas of floodplain alder or other water-demanding deciduous species should be discouraged if they were not part of the natural vegetation, as they reduce summer low flows.
- Single-tree forest health treatments should be carried out when damaging insects such as bark beetle threaten the RMA. Preferred strategies include prevention and suppression (see the Bark Beetle Management Guidebook).
- Broadcast burning within an RMA is not recommended.
- Vegetation control using domestic livestock is not permitted within RMAs in community watersheds.
- Methods of mechanical site preparation that create high ground disturbance are not recommended within RMAs because of the risk of sediment entering streams.
- Certain pesticide applications may be permitted within an RMA, but a minimum 10 m pesticide-free zone must be maintained beside all streams. Refer to section 13 "Pesticide management."
- Approved fertilizers are permitted within an RMA, but a 10 m fertilizer-free zone must be maintained beside all streams that can be seen from the air during application. Refer to section 12 "Forest fertilizer management" for detailed management prescriptions.
Range practices within RMAs are described in section 10 "Range management."
Terrain hazard mapping and field assessments are required in community watersheds to provide information about terrain and soil conditions that may pose either a landslide or surface erosion hazard to water quality.
Terrain stability maps show the distribution of stability conditions across an area. They identify areas that require field assessments of terrain stability prior to approval of road construction, cutblock boundaries, timber harvesting methods and silviculture systems. Hazard maps and assessments are commonly used with other resource information to plan forest development. In particular, they allow forest planners anticipate and avoid areas where harvesting or road building could damage the environment.
Requirements:
Forest development plans
- Forest development plans must describe, for the area in the plan, the location and nature of areas with a moderate or high likelihood of landslides and, if within a community watershed, areas with a high or very high surface erosion hazard.
Terrain stability and surface erosion hazard field assessments
- During the three years following community watershed designation, a terrain stability and erosion hazard field assessment must be carried out on all areas proposed for harvesting on slopes steeper than 60 per cent, on all areas proposed for road building and on all areas affected by this harvesting or road building.
- Three years after community watershed designation, terrain stability and erosion hazard mapping must be carried out for the entire area under the five-year forest development plan that is within a community watershed.
- Five years after community watershed designation, terrain stability and surface erosion hazard mapping must be carried out for the entire area of the long-term forest development plan that is within a community watershed.
The regulations on terrain mapping in community watersheds are described above under “Requirements.” There is a three- to five-year phase-in period, after which the area covered by the long-term forest development plan must be mapped.
However, the entire operable area of a community watershed should be mapped at one time. It is difficult to separate areas potentially affected by development from areas that are not. Hillside areas above potentially unstable slopes affect the stability of the site, and hillslope characteristics below a potential landslide affect sediment delivery to the stream. Given the small average size of a community watershed, it is more practical and efficient to simply terrain map the entire operable area. These maps can then be used for planning roads and harvest blocks.
Detailed interpretations of terrain stability should be based on terrain mapping conducted at survey intensity level C, as specified in the Mapping and Assessing Terrain Stability Guidebook. In some circumstances it may be appropriate to map at intensity level B, for example in watersheds or parts of watersheds with very complicated or hazardous soil and terrain conditions. However, mapping costs for level B surveys are higher than for level C. Moving from a level C to a level B survey should be based on professional judgment and consultation with regional geomorphologists.
The recommended map scale to show terrain and hazard information for forest management planning is 1:20 000 or greater. Topographic base maps should be used for map presentation when available (e.g., 1:20 000 scale terrain resource information management (TRIM) maps with 20-m contour intervals). Enlarged 1:50 000 scale contour maps should not be used.
Use the Terrain Stability Classification System for British Columbia (revised edition, 1988) for all detailed terrain mapping. Follow the recommendations on mapping standards and procedures in Guidelines and Standards for Terrain Mapping in British Columbia (1996). All of the following interpretations are described in Mapping and Assessing Terrain Stability Guidebook. Consult this guidebook for a full description of the hazards and interpretive classes.
Terrain stability mapping
Use the five terrain stability classes described in Terrain Stability Classification System for British Columbia to describe the likelihood of landslides in each terrain polygon. This provides a relative ranking of the likelihood of a landslide occurring after timber harvesting or road construction. This planning tool flags potential problem areas. It is not for on-site prescriptions and gives no indication of the expected magnitude or potential of landslide damage.
Landslide stream sedimentation hazard mapping
Landslide stream sedimentation hazard is the probability that a landslide will hit a stream. The three hazard classes in Table 7 of the Mapping and Assessing Terrain Stability Guidebook describe the potential for a landslide anywhere in a terrain polygon to hit any stream, regardless of stream class or order. The terrain mapper makes this interpretation.
Soil erosion hazard
Soil erosion hazard maps are derived from the terrain map by the terrain mapper. The maps should be prepared from C or B level terrain maps (see Mapping and Assessing Terrain Stability Guidebook). The maps identify terrain that may generate sediment after road or excavated trail construction. Use the five soil erosion hazard classes in Table 6 in the Mapping and Assessing Terrain Stability Guidebook, modified by the following criteria.
The following soil types generally have a very high soil erosion hazard:
- lacustrine, glacio-lacustrine or aeolian soils, steeper than 15 per cent
- glaciofluvial or fluvial sands, low bulk density, steeper than 30 per cent or gullied
- gullied peat or tufa, any slope
- colluvial deposits derived from above materials.
The following soil types generally have a high soil erosion hazard:
- lacustrine, glacio-lacustrine or aeolian soils, less steep than 15 per cent
- glaciofluvial or fluvial sands, low bulk density, less steep than 30 per cent
- other glaciofluvial sands, steeper than 30 per cent
- morainal blanket (deep till), steeper than 60 per cent, or steeper than 30 per cent if gullied
- colluvial deposits derived from above materials
- colluvium derived from soft, friable rock, steeper than 60 per cent, or steeper than 30 per cent if gullied.
Sediment delivery to streams
Use the five classes in Table 7 of the Mapping and Assessing Terrain Stability Guidebook to identify the potential for sediment delivery to a stream if soil erosion occurs. The terrain mapper makes this qualitative assessment.
The mapping described above is a "red flag" system for identifying sensitive soils and terrain. These areas can also contain less sensitive terrain. A natural bench on an otherwise steep hill, for example, may allow a road to be constructed with low landslide hazard. Or an area with well-drained, broad ridges between gullies may be suitable for aerial group-selection harvesting, despite the general high instability of gullied areas. Slope stability mapping at the 1:20 000 scale can always be refined by detailed field assessment.
Based on field assessments, the four important restrictions below may come into force.
- No timber may be harvested in an area with:
- a very high surface erosion hazard and a moderate to high risk of sediment delivery
- a high likelihood of landslides following timber harvesting.
- Clearcutting is not permitted in an area with a moderate likelihood of landslides and a high risk of sediment delivery to a stream.
- Road construction on areas identified as having a moderate or high likelihood of landslides or a high or very high surface erosion hazard must be designed by a person who, in the opinion of the district manager, has sufficient training and experience and, after June 15, 1997, by a professional engineer or professional geoscientist.
- Excavated or bladed trails are not permitted on any site with:
- a moderate or high likelihood of landslides or a high surface erosion hazard, and
- a moderate to high risk of sediment delivery to a stream.
The exception to this last regulation is where aerial or cable timber harvesting is done or where similar minimal impact ground treatments are specified in the silviculture prescription.
These specific areas require field assessments:
- all proposed roads, if no terrain mapping has been completed
- areas proposed for road construction that were identified during terrain mapping as having a moderate or high potential for landslides following road building, or areas where field staff have found indications of instability
- areas proposed for road construction that were identified during terrain mapping as having a high or very high hazard for surface soil erosion
- areas proposed for timber harvesting with slopes over 60 per cent, or identified as unstable or potentially unstable, if no detailed terrain mapping has taken place
- areas proposed for timber harvesting that were identified during terrain mapping as having a moderate to high likelihood of landslides. In the interior, a field assessment is not required for areas with a moderate likelihood of landslides, if cable or aerial harvesting methods are proposed.
- areas proposed for ground-based timber harvesting that were mapped as having a high or very high surface erosion hazard and a moderate or high risk of sediment delivery
- on the coast, all areas identified as having gullied terrain [3]
- any additional areas required by the district manager.
Terrain stability field assessments
Terrain stability field assessments are carried out in the areas described above by professional geoscientists or professional engineers, based on their experience. There is no standard method for use by non-professionals. The field assessment report is described in the Mapping and Assessing Terrain Stability Guidebook.
Surface soil erosion field assessment
This assessment can be determined by either:
When the latter technician is assessing erosion along a proposed road, he/she should produce the following report:
- a map showing terrain units along the proposed road location. Terrain units divide the road into sections based on uniform terrain type. Wherever there is a change in surficial material, soil texture, slope angle or configuration, soil depth or soil moisture regime, a new treatment unit is created
- relevant information on slope hydrology, especially information on seepage
- assessment of downslope consequences
- the location of soil pits
- within each terrain unit, record on a standard field card the material type, texture, drainage and moisture regime, slope gradient and ongoing slope processes (e.g., ravelling or creep)
- complete the Surface Soil Erosion Hazard Key on page 13 of the Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes Guidebook)
- some problem soil types are not adequately covered by the key. Where encountered, these should be rated high hazard (H) on gentle slopes or very high (VH) on steep slopes. Problem soil types include:
- well sorted, water- or wind-deposited sands and silts
- soils with very low (<30 per cent) coarse fragment content
- soils with a low bulk density, such as volcanic ash soils
- some soils derived from soft friable rock.
- describe the adequacy of the road location and identify alternative routes that would pose fewer problems.
Gully assessments
Follow the keys in the Gully Assessment Procedure Guidebook. This procedure is completed by the person completing the silvicultural prescription. Amendments to the guidebook in 1997 will include a key for road crossings of gullies.
