SALMONID GUIDELINES FOR
FORESTRY PRACTICES IN CALIFORNIA
February 8, 2000
The goal of this document is to protect and conserve federally listed salmonids in California by providing guidance to the State's timber management program that will allow for the attainment of healthy, functioning aquatic and riparian ecosystems. These guidelines are intended to assist the State of California in modification of the California Forest Practice Rules (FPRs), such that the forestry practices on non-federal lands will provide the ecosystem functions necessary for the conservation of salmonids. These guidelines are based upon conservation strategies for the following seven areas: Stream classification, riparian, roads, unstable areas, restoration activities, watershed analysis and assessment of cumulative watershed effects, and monitoring and adaptive management. A conservation approach for salmonids and their habitat in California must include all seven areas.
Definitions and descriptions of the terminology used in the guidelines are also provided.
1. Stream classification
Effective conservation of fish habitats and populations requires specific geographic knowledge of existing and potential fish habitats as well as the higher elevation, non-fish bearing stream systems that create and influence them. Ideally, a stream classification system should be based on functions and processes in the stream continuum. Forest practices should be tailored to protect and reinforce the functions and roles of at least three different stream classes in the continuum of the aquatic ecosystem: (A) fish-bearing streams that are currently or potentially capable of supporting fish of any species, perennially or seasonally; (B) perennial, non-fish bearing streams, which include spatially intermittent streams, and seeps and springs connected to them; and (C) seasonal, non-fish bearing streams (intermittent or non-perennial), which flow water, of any flow volume, some time during the water year, and seeps and springs connected to them. Seasonal streams may support aquatic life and contribute nutrients, water, gravel and large woody debris beneficial to the downstream aquatic ecosystem. Seasonal streams can also transport deleterious amounts of sediment, particularly fine sediment, to fish habitats. (1-3).
The National Marine Fisheries Service (NMFS) believes that forest management activities within riparian areas adjacent to, or above, streams may result in significant adverse impacts to salmonids and their habitats. Forest management activities may cause; (1) changes in stream temperatures, (2) increased sediment levels, (3) altered composition and abundance of fish species and macroinvertebrates, (4) destabilized streambanks and streamside areas, (5) reduced in-stream structural complexity, (6) reduced large woody debris recruitment, and (7) altered peak and base flows. Furthermore, the presence and use of roads within this area may contaminate water, create barriers to migration, reduce stream shading, reduce large wood recruitment to the stream, and increase sediment levels by accelerating the frequency and size of mass wasting events and elevating the amount of fine sediment delivered to streams.
These adverse effects are caused by disruption of the riparian functions that maintain salmonid habitat. Vegetation within riparian areas greatly influences the biological and physical processes that provide freshwater habitats for salmonids. These ecosystem roles include maintenance of shade and cover, water quality and flow routing, the aquatic food web, sediment routing and composition, stream channel bedform and stability, and linkages to side channels and the floodplain (4-8). Riparian vegetation produces habitats for salmonids, and its roles vary with the position of the stream reach in the fluvial network (9). Forestry practices have the potential to affect freshwater habitats for salmonids through changes in the characteristics of, and inputs from, streamside vegetation (10-13). In addition, timber management activities within riparian areas of tributaries above salmonid habitat should provide for adequate canopy, streambank and near-stream stability, and allochthonous inputs (large woody debris, litter, and nutrients) (2, 3). Activities within the upstream reaches of the watershed should not significantly increase the amount of sediment delivered downstream or modify the rate and timing of runoff.
A strategy to address these adverse effects must consider and adequately address the impacts of management on riparian functions important to salmonid habitat (14). Riparian zone width, management, stand composition and stocking objectives may vary regionally depending upon variation in stand composition, site tree height, geology, slope, and baseline conditions. Activities including salvage, site preparation, silvicultural methods, and yarding shall be addressed. Riparian zones shall be established that provide the following stream and riparian functions:
a. Floodplain and riparian connectivity
The concept of floodplain and riparian connectivity recognizes the complex ecological functions occurring in floodplain forests and should expand the riparian protection area to conserve these functions (summarized in Spence et al. 1996 (15) and Gregory et al. 1991 (16)). Floodplains may be both sources or sinks of organic materials and sediment over many years. Both understory vegetation, downed wood, and overstory trees promote floodplain storage of these materials. In these areas, organic materials are processed into forms that are more easily transported and utilized by stream biota. During periods of high flows, floodplains may also serve as refuge habitat for salmonids displaced from the main channel. The hyporheic zone, another important stream environment for fish reproduction and shelter from high streamflows, is the area of flow below the streambed that may extend vertically to depths of several meters and laterally from tens to hundreds of meters depending on channel confinement and floodplain geology (3). Widths necessary to protect these functions depend on site characteristics and flood magnitudes. In general, the flood prone zone includes riparian forests that occur on floodplains and low terraces along channels that migrate rapidly (on a geologic timescale) over their valley floors. If a flood prone zone is present, riparian zones are measured from its outer edge, so the stream and flood prone zone are protected together. Where the flood prone zone is not present, riparian zones should be established from the bankfull stage.
Where channels are prone to lateral migration or avulsion, riparian zones should be established that consider channel migration rates. The extent of the riparian stand where channel migration occurs should ensure that over time, riparian functions will be maintained and the channel will not migrate out of riparian zones.
b. Shade and microclimate
An important product of riparian vegetation is shade, which moderates air and water temperatures. Reduced shade leads to increased water temperatures, which can reduce the success or survival rate of salmonids during adult upstream migration, juvenile rearing, and downstream migration of smolts. Increased water temperatures can obstruct adult migration and limit spawning success, trigger early juvenile outmigration resulting in decreased survival rates (16), change juvenile sheltering behavior (17), reduce disease resistance, and increase metabolic requirements (16).
There appears to be a strong latitudinal component to stream temperatures, with warmer annual maximum monthly stream temperatures and warmer annual minimum monthly stream temperatures in California than in Washington and Oregon (18). However, studies indicate that air temperature and relative humidity are not significantly altered if buffer strips exceed 45 m (150 feet) in width (19-21). Buffer strips wider than this distance are likely necessary to maintain ambient conditions in managed second-growth stands and in relatively dry, inland, low elevation forest types. The NMFS recognizes the need for additional information on depth-of-edge effects into riparian stands in dry, inland forest types.
There is a lack of information on the effects of management on the temperature of small perennial non-fish bearing streams, and on the cumulative effects of temperature increases in perennial streams on larger downstream fish bearing reaches. The loss of shade and microclimate from riparian vegetation in tributaries above salmonid habitat may increase downstream temperatures (2).
c. Litterfall and nutrients
Riparian vegetation also provides the majority of the energy for the food web in heterotrophic systems by providing the allochthonous inputs supporting aquatic macroinvertebrates (22) and influencing the rate of nutrient spiraling (10, 23). Nutrient input and retention, litter fall (10), and shade functions (10) are affected by conditions within 0.5 to one site potential tree height from the channel. Allochthonous inputs are most important to small-sized streams with instream roughness elements that retain organic litter and breakdown products (23-25).
d. Large woody debris
Large woody debris from coniferous trees is an important component of freshwater salmonid habitat. It is provided to stream systems from hillslope processes such as debris torrents (26, 27), and from adjacent and upstream riparian vegetation. Woody debris routes sediment and peak flows, influences stream channel bedform and bank stability, and provides hydraulic refugia and cover within stream systems (10, 11, 28-33), thus influencing the formation and maintenance of the spatial template within which salmonids exist (8, 9). This template includes pool-riffle bedforms, backwater and edgewater habitats, and cover that provides adult spawning and holding habitat, juvenile summer and overwintering habitats, and refuge habitat from high velocities and predation (8, 35). Reduction in the quantity or quality of any of these habitats may result in reduced survival of salmonids during the life-history stages in which those habitats are used (35-37). Juvenile salmonid abundance is often directly related to the amount of large woody debris in a stream (38). Large woody debris is less susceptible to being lost under high flow conditions, creates deeper pools, provides increased surface area for macroinvertebrates, and is more likely to capture floating wood (resulting in increased habitat cover) than smaller debris (10, 28, 30, 31, 33, 34, 39). Woody debris also plays a key role in the retention of salmon carcasses (40), a major source of nitrogen and carbon in stream ecosystems (41).
Forest management activities within the riparian zone have the potential to change the distribution, size, and abundance of large woody debris in streams (12, 36, 42) and to simplify stream channels (35). Streams are severely depleted in large woody debris due to splash-damming, stream cleaning, and harvest of trees in the riparian zone (14, 35, 43). Large pieces, particularly conifers, are longer-lasting and more stable, thus providing greater habitat benefits (12, 42, 44). As a result of past practices, riparian stand conditions have been transformed from conifer to hardwood-dominated in many areas along the Pacific Coast, with a significant reduction in both long and short term recruitment potential of conifer large woody debris (35).
Both McDade et al. 1990 (45) and Van Sickle and Gregory 1990 (46), reported that more than 90% of instream wood identified as coming from adjacent riparian sources came from within approximately one site potential tree height for mature stands of Douglas fir, and in tributaries to Redwood Creek (Humboldt County, California) approximately 64% of the variability of large organic debris loading is explained by the variability in the number of mature redwood trees per hectare within 50 m of the streambanks (31). Information on site tree height values for mature conifer stands can be obtained from McArdle and Meyer 1961 (47) for Douglas fir, Lindquist and Palley 1963 (48) for redwood, and Dunning 1942 (49) for Sierra Nevada mixed conifer forests.
Using mature, late seral site class for riparian zone widths is preferable to a set age class due to the variability and diversity of California forest types and current stand conditions. Variations in soil type, geology, tree species, climate, latitude, and elevation, result in numerous forest types across the state. Additionally, variations in stand condition can result in very different size classes for the same species on the same soil type within a set age class. For example, at 100 years of age redwood may achieve less than two-thirds of its maximum site-potential height. Redwood stands approaching 200 years of age lack many of the ecological attributes and habitat values of older forests (50). In order to obtain large trees for future recruitment throughout the range of forest types supporting anadromous salmonids, the NMFS believes that using a mature, late seral site class for riparian zone widths is necessary.
Forest management needs to account for the interactions between large woody debris recruitment and other factors. For example, windthrow is one mechanism for recruiting large woody debris into aquatic systems. However, effects of windthrow on riparian trees left in buffer strips can be severe, particularly when management opens up a stand (i.e., clear cut, group selection, shelterwood, etc.) adjacent to buffer strips (13, 51). A strategy for riparian zones should consider situations where windthrow may remove shade from large areas of stream channels or where recruitment rates of large woody debris should be maintained at rates similar to those for undisturbed stands (13).
Woody debris in upstream reaches routes sediment and organic debris (52); the loss of large woody debris in these upstream reaches may result in excessive sediment transport into salmonid habitat (26, 53, 54). A paucity of large woody debris in these upstream reaches will result in less large woody debris available for movement downstream into salmonid habitat through naturally occurring mass wasting events.
e. Surface erosion
Riparian vegetation and downed wood can also act to control sediment inputs from surface erosion (25). Site features such as slope, soil type, and drainage characteristics, riparian vegetation and associated downed debris, duff, and litter can filter overland flows from adjacent hillslopes. Megahan and Ketcheson 1996 (55) determined that overland sediment movement in the Idaho batholith was inversely proportional to obstructions (downed vegetation) on the hillside. Channel reaches subject to intense broadcast burns show increased erosion from loss of woody debris that stores sediment and enhances channel roughness (56). Increases in overland flow and surface erosion on schist slopes in Redwood Creek in northern California are associated with logging activities that compact soils, remove vegetation and litter, and create depressions that concentrate runoff and promote rill and gully erosion (57).
Upstream reaches, including intermittent and ephemeral streams, carry sediment, nutrients, and woody debris from upper portions of the watershed downstream to salmonid habitat. The quality of salmonid habitat is determined, in part, by the timing, speed, and amount of organic and inorganic materials transported downstream from reaches above salmonid habitat (58). Management activities that increase sediment inputs upstream of salmonid habitat may impair important habitat components, such as deep pools and clean spawning gravels, in downstream reaches (2, 3).
f. Stream bank stability
Streambank stability depends, in large part, on intact roots and embedded and fallen logs, and some riparian areas that were clearcut or salvaged in the past few decades may lack a high degree of this stability (8, 34). Streambank stability is maintained if riparian stands are undisturbed within a distance of 0.5 to one site potential tree height (34). This protection is expected to encourage the growth of dense live root mats along the entire length of streams, provide a source of large woody debris, and allow natural processes of channel shift and scour to interact with a mature forest and natural bank materials (25).
Roads can adversely affect salmonid habitat by increasing sediment loads, altering channel morphology and destabilizing streambanks, modifying the drainage network, creating barriers to movement, and increasing the potential for chemical contamination (59). The objectives for the management of roads (construction, reconstruction, upgrading, maintenance, and use) include the following:
The impact of roads on salmonid habitat can be addressed with improved design, surfacing, construction compliance, control of use during sensitive times, closure and/or decommissioning of environmentally sensitive roads, and long-term maintenance (14). Environmentally sensitive roads are generally located in close proximity to streams, or on lower hillslope and midslope locations where unstable terrain and high maintenance costs are common. NMFS encourages the development and implementation of a NMFS-approved road management plan and long-term transportation plan, at the ownership or watershed scale. This plan should inventory and assess the condition of both existing and legacy roads, plan and implement the proper maintenance or decommissioning of roads, minimize construction of new roads, upgrade existing roads to meet the above objectives, remove artificial barriers to fish passage, and identify a long-term road network that will result in low environmental impacts and low annual maintenance requirements and costs. The plan should also develop strategies for controlling winter and wet weather road use. Road inventory, improvement, and permanent decommissioning of environmentally-sensitive roads, along with monitoring, and maintenance can help to protect salmonids by decreasing sediment delivery to waters containing the species. The NMFS recommends the "Handbook for forest and ranch roads: A guide for planning, designing, constructing, reconstructing, maintaining, and closing wildland roads" (60) as a reference for road-related activities. Additional information can be obtained on road surfacing in "Reduction of soil on forest roads"(61).
A road strategy must provide guidelines for construction, reconstruction, upgrading, maintenance, and use that maintain and improve water quality and stream habitats by addressing the following impacts:
a. Generation and routing of fine sediment
Construction of a road network can greatly accelerate erosion rates within a watershed (62-70). Cederholm et al. 1981 (71) reported that the percentage of fine sediments in spawning gravels increased above natural levels when more than 2.5% of a basin area was covered by roads. Roads and other areas of intentional surface disturbance are a chronic source of sediment to streams (72). Roads and related ditch networks are often connected to streams via surface flowpaths, providing a direct conduit for the sediment. Where these roads and ditches are maintained by periodic "blading," chronic sediment delivery may be temporarily increased as bare soil is exposed and ditch roughness features which store and route sediments are removed. Recommended approaches to minimize or avoid fine sediment discharge from roads include: divert road run-off to the forest floor by disconnecting the road surface from the hydrologic network using outsloping, rolling dips, and appropriately spaced ditch relief culverts; decommission or upgrade environmentally sensitive roads; stockpile and use erosion controls during road construction, reconstruction, and upgrading; control use when road surfaces are prone to erosion during periods of wet weather; surface all roads and road crossings adjacent to streams; minimize through cuts and road surface area; limit road use, construction, reconstruction, blading, or upgrading to dry periods; inspect roads prior to winter rains and during storms to remove material clogging culverts; perform annual maintenance on all roads to ensure drainage structure and facilities are in proper condition; construct or reconstruct roads such that they require little or no maintenance.
b. Generation and routing of coarse sediment
In steeper terrain, road construction may trigger landslide processes that deliver large amounts of sediment directly into streams (59). Improperly maintained roads may still fail, years after construction (59). Roads built near waters can deliver sediment to streams, destabilize streambanks, and constrain the natural geomorphological migration of the stream channel. Road networks can affect hillside drainage; intercepting, diverting, and concentrating surface and subsurface flow, and increasing the drainage network of watersheds (73, 74). This can lead to changes in peak and base flows in streams. Stream crossings can restrict channel geometry and prevent or interfere with migration of adult and juvenile salmonids (59). Crossings can also be a source of sedimentation, especially if they fail or become plugged with debris, causing significant cumulative impacts downstream (59, 75). Hagans and Weaver 1987 (65) found that fluvial hillslope erosion associated with roads in the lower portions of the Redwood Creek watershed produced about as much sediment as landslide erosion between 1954 and 1980. Similar results are reported by Best et al. 1995 (63), attributing most of the sediment to stream diversions at crossings. Inventory and assessment of the road network is required in order to locate those sites with high erosion hazards and prioritize them for upgrading or decommissioning according to the risk they pose to aquatic resources of concern (76).
c. Physical impediments to fish passage
Beechie et al. 1994 (77) found that 13% of historical coho salmon habitat in a large river basin in Washington was rendered inaccessible by culverts. Culverts may allow for adult fish to pass but not juvenile stages. Because the timing of juvenile upstream migration differs from adults, flow-limits for each life stage need to be considered such that culverts can pass both life stages. Recommended approaches to allow for fish passage include: limit road crossing construction to periods when impacts to salmonids can be minimized or avoided; where culverts are used they should be sized to permit passage of a 100-year recurrence flood without overtopping the culvert inlet; construct or reconstruct water crossings such that they do not change the channel bed elevation, block sediment transport downstream, and maintain channel cross-sectional area at least to the bankfull stage; design culvert crossings to allow for passage of all life stages of salmonids (14). NMFS guidance on stream crossings is forthcoming.
d. Streamside-adjacent roads that alter fluvial processes and disrupt riparian functions
These are roads that generally have an alignment parallel to the alignment of a stream, where riparian functions and fluvial processes can be altered or disrupted by the presence of the road. In general, these roads are likely to deliver fine sediment to streams due to their proximity. Consideration should be given to providing mitigation for the functions altered by the road, such as replacement of stems lost to the road prism, placement of trees that have fallen across the road fill or cutslopes to the streamward side of the road, prevention of delivery of fine sediment by road surfacing, disconnecting of the road drainage network from the stream system, or decommissioning.
e. Road drainage impacts to stream hydrology
Road networks can affect hillside drainage; intercepting, diverting, and concentrating surface and subsurface flow, and increasing the drainage network of watersheds (73, 74). This can lead to changes in peak and base flows in streams. Recommended approaches to minimize impacts of road drainage on stream hydrology include disconnecting the road drainage network from streams by reconstructing roads and runoff ditches using outsloping, rolling dips, and cross-drains at frequencies specified by Weaver and Hagans 1994 (60).
4. Unstable areas
Tectonic activity, soils prone to erosion and naturally unstable parent material, high precipitation, and steep slopes characterize much of the landscape along the California Coast. This combination leads to a landscape dominated by mass movement processes (78) and high levels of sediment in streams. Unstable slopes in coastal northwestern California are some of the most rapidly eroding terrain in the United States (79). It is indicative of a landscape that is abnormally sensitive to destabilization by management activities. The south fork of the Eel River, northern California, has one of the highest sediment yields in the United States (80, 81). Streams in the Coast Range of Northern California, for example, annually export 2,600 tonnes of sediment per km2, compared to 53-102 tonnes of sediment per km2 in Oregon's Coast Range (82) and 66 tonnes of sediment pre km2 for coastal Washington timberlands (83). Mass failures are a major source of sediment into streams. In the Redwood Creek basin, approximately 80% of the landslides occur on slopes of 50% gradient or more (84). In sediment-poor streams, mass wasting may bring in needed coarse sediment and large woody debris (85), but sediment impoverishment is typically not a significant issue in managed basins of northwest California. Usually, mass movements bring sediment into higher-gradient channels, and the sediment is then carried downstream into depositional reaches, potentially impairing rearing and spawning functions (58). Depending on the amount of material transported, the velocity, and the channel gradient, mass failures that deliver sediment to streams can increase sediment loads, partially or completely block channels, scour streambeds, creating significant cumulative impacts downstream (72).
Mass movement frequency has been strongly linked to the type and intensity of land management within watersheds (58, 84, 86). In Redwood Creek, the number of streamside landslides increased from 100 in 1947 to 415 in 1976, due mostly to debris sliding following periods of intensive timber harvest, road construction, and large storms (84). In recent times, sediment contributions related to land use account for 30-60% of the total sediment loads in northern coastal California rivers (87). Timber management activities that undercut hillslopes, increase surface weight, alter surface and subsurface flows, and reduce root strength strongly influence slope and soil stability (78). In some areas, management-related mass wasting events are primarily associated with roads and their drainage systems, while in other areas landslides are common on open slopes after logging activities (88, 89). Impacts to salmonids may occur if mass failures caused by timber management activities deliver sediment to salmonid habitat or block or impair migration.
The goal of a management strategy for unstable slopes should be to prevent or avoid an increase or acceleration of the naturally occurring rate of landslides due to forest practices. At a minimum, known unstable or potentially unstable geomorphic features including but not limited to inner gorges, headwalls and headwall swales, toes of deep-seated slumps or earthflows, and debris torrent tracks should be protected. However, due to landscape variability and sparsity of assessment information, watershed-specific approaches to manage unstable areas should be developed through watershed analysis (see below). Management strategies for unstable areas should include: geologic consideration for road construction, reconstruction, and upgrading of roads on unstable areas; silvicultural prescriptions (i.e., uneven age management vs. even age management); harvest methods (i.e., ground based vs. full suspension); and salvage of downed wood. However, the reduction in landslide risk provided by uneven age management (or leaving a percentage of trees) in unstable areas is unknown and should be assessed through watershed analysis, monitoring, and adaptive management.
Certain restoration activities such as bank stabilization, importing large woody debris, placement of instream structures, importing spawning gravel, etc., often involve altering habitat conditions required by salmonids. Restoration activities may increase sediment levels, alter or divert stream flows, change channel geometry, and block migration. If done properly, at the appropriate time of year, many of these impacts will be temporary (e.g., increased sediment levels) and habitat condition will eventually improve. If improperly planned and executed, restoration activities can provide only temporary improvements ('Band-Aids') or, in the worst cases, actually degrade salmonid habitat. To conserve salmonids, restoration activities that involve management within or adjacent to water should not be proposed unless they have been identified as necessary in a NMFS-approved watershed restoration plan developed through the completion of a NMFS-approved watershed analysis (see below).
6. Watershed analysis and cumulative watershed effects
Ideally, the impacts of forest management activities on watershed processes that affect salmonid populations and their habitats should be addressed through an agency or landowner-prepared, NMFS-approved, watershed analysis to develop watershed-specific prescriptions. A watershed analysis is necessary to: adequately evaluate watershed baseline conditions and history of past management; develop a watershed-specific unstable area strategy based on identification of potentially unstable slope features; develop a watershed-scale road plan that prioritizes road decommissioning and upgrading; develop watershed-specific information regarding fish use of streams and stream potential for fish habitat; develop a watershed-specific strategy to prevent or avoid the effects of forest management on stream hydrology; provide a prioritization for watershed restoration, including fish passage barriers at road crossings; determine monitoring and adaptive management needs at the watershed level; and assess cumulative effects of numerous timber and non-timber-related activities occurring within watersheds (14, 90). Fundamental to the assessment of cumulative effects is the evaluation of reasonably foreseeable future activities in the watershed. The NMFS recommends that a repeatable methodology that is comparable across landscapes be developed in coordination between NMFS and State of California agencies with expertise in salmonid biology, ecology, and physical landscape processes.
7. Monitoring and adaptive management
A monitoring and adaptive management program is necessary to monitor and assess implementation of forest practice rules and achieve desired resource objectives (14). Monitoring should be based on objectives and should be repeatable, using comparable methods across landscapes. Successful adaptive management includes the following elements: a set of protocols and standards to define and guide execution of the process; a set of participants empowered to conduct the required activities; a baseline data set used to monitor change; a formalized dispute resolution process that includes time lines for decision-making processes; a defined process for proposing any new rules or rules changes that may be necessary; and adequate funding to conduct the necessary research, monitoring, and peer review. In addition, the adaptive management program will include participation by the NMFS in each of the elements. Should monitoring or new scientific knowledge lead the agencies to amend regulations, proposed changes will be available for public review and comment. NMFS will make a final determination whether the changes are adequately protective of listed salmonids. Finally, a monitoring and adaptive management program should be coordinated with, and support and/or be supported by, watershed analysis, assessment of cumulative effects, and restoration plans.
Bankfull stage: The point on a streambank at which overflow into the active floodplain begins. The active floodplain is a flat area adjacent to the channel constructed by the stream and overflowed by the stream at a recurrence interval of about 1.5 to two years (91). If the active floodplain is absent or poorly defined, other indicators may identify bankfull. These include the height of depositional features, a change in vegetation, slope or topographic breaks along the bank, a change in the particle size of bank material, undercuts in the bank, and stain lines or the lower extent of lichens on boulders. Deposits of organic debris are seldom good indicators of bankfull. Harrelson et al. 1994 (92) provides a field guide for determining bankfull. Field determination of bankfull should be calibrated to known stream flows or to regional relationships between bankfull flow and watershed drainage area to avoid errors. Procedures for calibrating field-identified bankfull stage with stream gauge data are described in Rosgen 1996 (93).
Flood Prone Zone: Spatially, this area generally corresponds to the modern floodplain, but can also include river terraces subject to significant bank erosion. For delineation, see definition for floodplain.
Debris torrent tracks: Swales, gullies or watercourse channels susceptible to debris torrents. Channels may show recent evidence of debris flow(s) and have the potential to deliver future debris torrents. Characteristics of channels prone to debris torrents are described by Benda 1985 (94).
Floodplain: The area adjacent to the stream constructed by the river in the present climate and inundated during periods of high flow (91, 94).
Headwall: Steep (generally greater than 50 percent), planar or concave slopes at or near the heads of steep swales, gullies and Class II and Class III waters. Headwalls may be less steep and/or show little or no evidence of past failures where vegetation maintains slope stability.
Headwall swale: A concave depression, with convergent slopes generally greater than 50 percent that is connected to a water via a continuous linear depression. A linear depression interrupted by a landslide deposit is considered continuous for this definition. Many swales have no surface water but others contain seeps and springs. Headwall swales typically experience episodic evacuation of debris by shallow-rapid landsliding, followed by slow refilling with colluvium. Debris slides that begin within headwall swales commonly evolve into debris torrents, which have the potential to reach great distances downhill and downstream.
Inner gorge: An inner gorge is a geomorphic feature formed by coalescing scars originating from landsliding and erosional processes caused by active stream erosion and incision. The feature is identified as that area of a stream bank situated immediately adjacent to the flood plain or stream channel where a flood plain does not exist, generally having side slopes >50% in incompetent bedrock, and being situated below the first break in slope above the stream channel. Typically, inner gorge slopes are generally greater than 65% (33°), but Kelsey 1988 (95) notes that in Redwood Creek, inner gorge slopes average 27° (51%) in the upper valley and 21° (38%) in the lower basin.
Roads: For purposes of these guidelines, roads include all sites of intentional surface disturbance for the purpose of vehicular traffic and equipment use, including all surfaced and unsurfaced roads, temporary roads, closed and inoperable roads, legacy roads, skid trails, tractor roads, layouts, landings, turnouts, seasonal roads, fire lines, staging areas and base camps. This definition also includes all associated sites such as quarries, borrow pits, and spoil or waste areas.
Salvage: Removal of trees and their parts, including, 1) insect-attacked and/or diseased trees ("sanitation") and 2) dead, dying, or deteriorating trees or downed woody debris ("salvage") and trees that have fallen through bank cutting, landslides or wind throw. Snags that are felled to reduce fire hazards and for reasons of safety are included.
Swale: An unchanneled hillslope where subsurface flow is concentrated. Swales are often sites of accumulation of colluvium. Combination of concentrated flow and unconsolidated colluvium can lead to hillslope failure.
Unstable areas: In addition to the definitions contained in 14 CCR 895.1 (96) for unstable areas, slide areas, and unstable soils, unstable areas include headwalls, steep swales, debris torrent tracks, inner gorges, debris slide slopes and streamside areas that have been undermined by stream bank erosion. Unstable areas include past and current mass movement features as well as geomorphic features indicating landslide prone terrain (78) where the potential for mass movement exists.