Narrative standards

(a) A river or stream segment classified as "Class 1" pursuant to the Stream Flow Standards and Regulations shall exhibit, at all times, the depth, volume, velocity and variation of stream flow and water levels necessary to support and maintain habitat conditions supportive of an aquatic, biological community characteristic of that typically present in free-flowing river or stream systems of similar size and geomorphic characteristics under the prevailing climatic conditions. (b) A river or stream segment classified as "Class 2" pursuant to the Stream Flow Standards and Regulations shall exhibit, at all times, the depth, volume, velocity and variation of stream flow and water levels necessary to support and maintain habitat conditions supportive of an aquatic, biological community minimally altered from that typically present in free-flowing river or stream systems of similar size and geomorphic characteristics under the prevailing climatic conditions. (c) A river or stream segment classified as "Class 3" pursuant to the Stream Flow Standards and Regulations shall exhibit, at all times, the depth, volume, velocity and variation of stream flow and water levels necessary to support and maintain habitat conditions supportive of an aquatic, biological community moderately altered from that typically present in free-flowing river or stream systems of similar size and geomorphic characteristics under the prevailing climatic conditions. (d) A river or stream segment classified as "Class 4" pursuant to the Stream Flow Standards and Regulations may exhibit substantially altered stream flow conditions caused by human activity to provide for the needs and requirements of public health and safety, flood control, industry, public utilities, water supply, agriculture and other lawful uses; and shall, while giving consideration to societal needs, economic costs, and environmental impacts, exhibit to the maximum extent practicable the depth, volume, velocity and variation of stream flow and water levels consistent with the narrative standard for Class 3 river and stream segments. The societal needs, economic costs, and environmental impacts to be considered shall include: (1) Extent of prior channel modification; (2) Current impact of development and impervious cover in the watershed; (3) Overriding societal needs that cannot otherwise be met; (4) Economic impact that would substantially impair or otherwise detrimentally affect the economy of the community in which the segment is located or of the state; (5) Associated environmental impacts to other river or stream segments; (6) Existing biological community; and (7) The margin of safety of the community water system utilizing the river or stream segment as an existing public water supply source.