2012-06-20_PERMIT FILE - C2010089 (87)

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Appendix 2 "ALLUVIAL VALLEY FLOOR" Legislative Directions and Interpretations Definition of Alluvial Valley Floor Consistent with HR 9725: "'alluvial valley floors' means the unconsolidated s deposits holding streams where water availability i for subirrigation or flood irrigation agricultural Source - 701(27) HR 25(94th) FURTHER DESCRIPTION "Alluvial valley floors refers to those unconsolidated deposits formed by streams (including their meanders) where the ground water level is so near the surface that it directly supports extensive vegetation or where flood stream flows can be diverted for flood irrigation." Source - p. 65, Conference Report HR 9725 (95th). ".,.alluvial valley floors are the upper, near - horizontal surface of the unconsoli- dated stream -laid deposits which border perennial, intermittent, or ephemeral streams. The alluvium that makes up the stream -laid deposits is composed of clay, silt, sand, gravel, or similar detrital material that has been, or is being, trans- ported and deposited by streams. Alluvial valleys within this definition are tra- versed by perennial or intermittent streams or by ephemeral stream channels: are irrigated in most years by diversion of natural flow or ephemeral flood flow on the modern flood plain and adjacent low terraces, or by subirrigation of the flood plain by underflow: and are used for the production of hay and other crops that are an in- tegral part of an agricultural operation." Source - ibid. "Excluded...are the colluvial and other superficial deposits that normally occur along the valley margins, are higher than the modern flood plain and low terraces, are not irrigated by diversion of natural flow or by ephemeral flood flow, and are not subirrigated by underflow." Source - ibid. "Alluvial valley floors do not include upland areas which are generally overlain by a thin veneer of colluvial deposits composed chiefly of debris from sheet erosion, deposits by unconcentrated runoff or slope wash, together with talus, other mass movement accumulation and wind blown deposits." Source - p. 83, Conference Report HR 25(94th) ".,.alluvial valley floors must be (an) integral part of a drainage network that tra- verses the area...These are part of a through flowing stream (hydrologic) system and are not small areas of Isolated internal drainage." Source - p. 65, Conference Report HR 9725(95th) "Some characteristics of alluvial valley floors which are essential for agricultural areas include: (l) sufficient runoff to allow for flood water irrigation each year; (2) development of flood plain and low terraces where water can be spread easily without significant mechanical alteration of the surface; and (3) shallow ground water where subirrigation is used and (which) therefore requires a minimum of valley floor dissection so that ground water is not drained." Source - pp. 82 -83, Conference Report HR 25(94th)