Pre-control/Pre-Construction Activities


Pro-control Activities

Pre-control activities include planning, design, permit acquisition, and surveying. Vegetation and fluvial geomorphic processes at a project site provide for natural creation and maintenance of habitat function. Pre-control activities that result in removal of vegetation will reduce or eliminate those habitat values (Darnell 1976, Spence et al. 1996).


Denuded areas lose organic matter and dissolved minerals, such as nitrates and phosphates. The microclimate becomes drier and warmer with a corresponding increase in soil and water temperatures. Loose soil can temporarily accumulate in the construction areas and, in dry weather, this soil can be dispersed as dust. In wet weather, loose soil is transported to a stream or water body by erosion and runoff, particularly in steep areas. Erosion and runoff increase the supply of soil to lowland areas, and eventually to aquatic habitats where they increase turbidity and sedimentation. This effect is amplified during high frequency and high duration flow events.


If the control action occurs adjacent to or near a stream, loss of vegetation on the project site will increase the rate of transport of water to the stream during rain events, which can lead to higher peak flows. Higher stream flows increase stream energy that scours stream bottoms and transport greater sediment loads farther downstream than would otherwise occur. Sediments in the water column reduce light penetration, increase water temperature, and modify water chemistry. Once deposited, sediments can alter the distribution and abundance of important instream habitats, such as pool and riffle areas. Fish that spawn in fish gravel require fresh, moving water to survive and grow and then an escape route after they have hatched. The introduction of excess sediment can have disastrous results for the spawning habitat of fish that require gravel substrate for spawning and for the habitat of gravel-dwelling benthic organisms (Castro and Reckendorf 1995). During dry weather, the physical effects of increased runoff appear as reduced ground water storage, lowered stream flows, and lowered wetland water levels.


The combination of erosion and mineral loss can reduce soil quality and site fertility in upland and riparian areas. Concurrent in-water work can compact or dislodge channel sediments, thus increasing turbidity and allowing currents to transport sediment downstream where it is eventually redeposited. Multiple control activities, in which the site is inundated, can significantly increase the likelihood of severe erosion and contamination.


Implementation of conservation measures can reduce, but not eliminate, the risk of soil erosion and increased sediment inputs to streams, thus reducing the likelihood of impacts to stream habitats. At a watershed scale, this risk is not expected to be significant because of the localized nature of the impacts and the anticipated widely dispersed locations of project sites in multiple watersheds across the CRB.


Pre-Construction Activities

 The primary habitat effect from preconstruction activities is a temporary and localized increased in turbidity and suspended sediment. Turbidity may have beneficial or detrimental effects on fish, depending on the intensity, duration, and frequency of exposure (Newcombe and MacDonald 1991). Salmonids have evolved in systems that periodically experience short-term pulses (days to weeks) of high suspended sediment loads, often associated with flood events, and are presumably adapted to high pulse exposures. Adult and larger juvenile salmonids may be little affected by the high concentrations of suspended sediments that occur during storm and snowmelt runoff (Bjornn and Reiser 1991), although these events may produce behavioral effects, such as gill flaring and feeding changes (Berg and Northcote 1985).


Deposition of fine sediments reduces egg incubation success (Bell 1991),  interferes with primary and secondary production (Spence et al. 1996), and degrades cover for juvenile salmonids (Bjornn and Reiser 1991). Chronic, moderate turbidity can harm new-emerged salmonid fry, juveniles, and even adults by causing physiological stress that reduces feeding and growth, and increases basal metabolic requirements (Lloyd 1987, Redding et al. 1987, Bjornn and Reiser 1991, Servizi and Martens 1991, Spence et al. 1996). Juveniles avoid chronically turbid streams, such as glacial streams or those disturbed by human activities, unless those streams must be traversed along a migration route (Lloyd et al. 1987). Older salmonids typically move laterally and downstream to avoid turbidity plumes (Sigler et al. 1984, Lloyd 1987, McLeay et al. 1987, Scannell 1988, Servici and Martens 1991). Fish exposed to moderately high turbidity levels in natural settings are able to feed, although at a lower rate and with increased energy expenditure due to a more active foraging strategy. Over a period of several days or more, reduced feeding resulting from increased turbidity can translate into reduced growth rates.


Turbidity also limits fish vision, which can interfere with social behavior (Berg and Northcote 1985), foraging (Gregory and Northcote 1993, Vogel and Beauchamp 1999) and predator avoidance (Miner and Stein 1996, Meager et al. 2006). This can have varying effects on fish growth and survival, depending on a range factors such as ambient light levels and depth; relative visual sensitivities of predators and prey; and non-visual sensory abilities. Conversely, salmon may benefit from increased turbidity; predation on salmonids may be reduced in water turbidity equivalent to 23 Nephalometric Turbidity Units (NTU) (Gregory 1993, Gregory and Levings 1998), which may improve survival.


Therefore, fish will be exposed to elevated turbidity and suspended sediment during pre-construction activities. Some juvenile salmonids may decrease feeding, experience increased stress, or may be unable to use the action area, depending on the severity of the increase in suspended sediments.