SI-2 (3/16/05 version)
Environmental Targets And Priorities, Stream Integrity, Stream/Watershed Components

Section 502 (19) of the Clean Water Act defines pollution as human-induced alteration of waters caused by pollutants as well as non-pollutant agents, such as flow alteration, loss of riparian zone, physical habitat alteration, and introduction of alien taxa. This definition is consistent with the State of Ohio definition of NPS pollution which includes consideration of polluted runoff and physical alterations to the stream as illustrated in the Water Resource Impact Diagram.

Stream systems are complex and their quality or integrity is dependent on both the stream components and the interactions/relationships between those components. Figure 1 illustrates one way to organize stream components and these relationships. Specifically, the stream components are shown in a nested hierarchy of variables. The stream components to the left, control the stream components on the right. Said another way, without the components on the left, the components and processes illustrated on the right would not exist.

Figure 1. Dominant Causal Relationships Between Stream Component Variables

Physical Inputs And Characteristics Of Streams

The stream inputs refer to key categories of background conditions OUTSIDE the stream channel that fundamentally influence what happens IN the stream channel. Once the inputs interface with the stream channel, the driving processes in the stream interacting with these inputs controls stream form or morphology.

Stream System Sub-Units

As illustrated in Figure 1, the first three tiers of causal factors control the presence/absence of the stream system components listed below and the associated habitat within these components. It is critical that the size or scale of the water resource is considered when applying an assessment protocol to determine water resource integrity.