List of Impairments
The term 'impairment' refers to conditions that have the potential to harm or reduce the ecological health or function of a creek. The following list of impairments have been used by other groups to indentify potentialy harmful ecologic conditions within creeks and were focused on for this project.
Patches of Exotic Invasive Vegetation
Many of the plants encountered along the creek during a stream walk are not native to this region and may originally be from other parts of the country or world. These exotic species have been imported here over time, usually by people, both accidentally and intentionally. While many of these species may not be a problem, some adapt well to the local conditions and thrive. Some of these species do so well that they begin to overgrow and displace native plants that may have previously thrived in the area. Often, the newer invasive species do not provide appropriate habitat for birds and wildlife that live in the area. The amount of bio-diversity may also be greatly reduced when a single invasive species totally takes over an area. Many restoration groups that value native plant diversity are interested in knowing where problematic areas are located in the watershed.
Unstable Stream Bank Conditions
As water flows down streams and creeks, it carries sediment with it from the banks and streambed. This sediment transport is a natural process, but as human land uses encroach on the stream channel, the process may be greatly magnified. Excessive sediment transport can cause banks to become unstable. Unstable stream banks are more susceptible to bank collapses and landslides, which greatly increase the sediment load in the streams. High sediment loads can increase turbidity in the creek, impairing water quality. Large quantities of sediment may be a burden on flow control infrastructure such as dams and man-made flood control channels. Bank collapses also may impair adjacent land uses and pose a potential burden to nearby structures.
Artificial Stream Bank Modifications
A common practice in urbanized areas is to artificially modify stream banks to make them more resistant to erosion and to provide higher flood control capacity. There are many ways to modify stream banks, but some of the most common methods involve removing the natural vegetation and replacing it with concrete or heavy rocks that protect the banks from erosion and speed up the flow of water through the channel. Although these modifications minimize erosion where they are located, the resulting increased flow velocity often causes greater erosion problems downstream. Poor planning when constructing these modifications can greatly impair the ecological function of streams.
Discharge Points and Outfalls
In all watersheds, water across the landscape will naturally flow to and accumulate in the creeks. In an urbanized landscape, humans build drains and gutters to channelize storm flow and runoff that falls over the entire landscape. All of this flow enters our creeks at individual discharge points and outfalls such as pipes and storm drains. Water flowing over an urbanized landscape carries trash and pollutants with it. If poorly managed, this trash and pollution flows directly into creeks, impairing water quality. Most resource managers do not have any sort of accurate inventory of the discharge points draining into their creeks.
Impacting Land Uses
Human land uses that are adjacent to creeks can potentially impact the environment and frequently act as pollution sources. Land uses of particular interest are those that have replaced the vegetation right up to the edge of the creek. Even though these land uses may not discharge directly into the channel, runoff may still carry pollutants to the creek. Water that flows off of parking lots and concrete surfaces into streams may carry oil, trash, and other pollutants. Landscaping that uses fertilizers and pesticides may act as a source of pollution. The presence of animals such as livestock and horses may also impair water quality.
Illegal Dump Sites
Unfortunately, people often use creeks as a location to illegally dispose of their garbage. Household trash, shopping carts, automobiles, and debris from homeless encampments are common types of materials found at dump sites in creeks.
Potential Barriers to Fish PassageSteelhead trout spend most of their time in salt water but travel up coastal creeks to spawn. These anadromous fish used to be common in our watersheds but have become rare due to a combination of creek impairments, the most obvious being blocked access to upstream spawning areas. As many restoration efforts exist to reintroduce steelhead trout into local creeks, the existence of both man-made and natural obstacles that act as potential barriers to fish migration is important information to resource managers.