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A cumulative impact has been commonly defined as: ""...the impact on the environment which results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency or person undertakes such other actions. Cumulative impacts can result from individually minor but collectively significant actions taking place over a period of time."" (U.S. Council on Environmental Quality 1978). A threshold is defined in Webster’s as ""the point at which a physiological or psychological effect begins to be produced."

. 1994. . (3,364k)

Abstract - Thermal stratification occurred in pools of three rivers in northern California when inflow of cold water was sufficiently great or currents were sufficiently weak to prevent thorough mixing of water of contrasting temperatures. Surface water temperatures in such pools were commonly 3-9°C higher than those at the bottom. Cold water entered pools from tributaries, intergravel flow through river bars, and streamside subsurface sources. In Redwood and Rancheria Creeks, cold water was protected where gravel bars encroached into pools that were scoured along bedrock banks, creating...

Abstract - I assessed characteristics of pools used by oversummering adults of summer steelhead Oncorhynchus mykiss between July and October 1991 in the New River, northwestern California. Most fish occupied channel confluence pools and other pools of moderate size (200-1,200 m 2); these pools had less than 35% substrate embeddedness and mean water depths of about 1.0-1.4 m. Microhabitat occupied during daylight hours included cover provided by bedrock ledges and boulders where water velocity averaged 9.3 cm/s (range, 1-34 cm/s; steelhead densities under this cover were highest at the...

We documented temperature stratification in a deep bedrock pool in the North Fork of the American River, described the diel movement of rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta. and determined whether these trout used cooler portions of the pool.From July 30 to October 10, 1992, the main study pool and an adjacent pool were stratified(temperature differences between surface and bottom were as great as 4.5°Q on all but two days.Six rainbow and one brown trout equipped with temperature-sensitive radio transmitters usedwater with temperatures ranging from 12 to 19.3°C....