Treesearch

Although it is unquestionably prudent to consider the cumulative watershed effects (CWEs) of timber harvesting, the presumed CWE phenomena offer limited opportunity for scientific inquiry. We are addressing two questions: are there synergistic sedimentation effects of sufficient magnitude to warrant consideration beyond efforts to reduce on-site erosion; and what are the expected long term effects of different harvesting schedules on fish habitat

A 160 km-long reach of Sacramento River was studied with the objective of predicting future changes in channel planform and their effects on water-surface elevations. Planform data were used to develop regression relationships between bend radius of curvature (Rc) and both short-term (5 years) and long term (90 years) lateral migration rates (MR) and migration distances (MD). A dimensionless cutoff index (Rc/MD) was developed to predict bend cutoff occurrence. Cutoffs occur when the cutoff index value is between 1.7 and 3.7. Channel planform controls water-surface elevations and bend...

Conventional engineering methods of flood control design focus narrowly on the efficient conveyance of water, with little regard for environmental resource planning and natural geomorphic processes. Consequently, flood control projects are often environmentally disastrous, expensive to maintain, and even inadequate to control floods. In addition, maintenance programs to improve flood conveyance and enhance levee stability, such as clearing riparian vegetation in channels and on levees, undergo little – if any – technical scrutiny. Such programs are often prescriptive in nature, rather than...

Retention of particulate and dissolved nutrients in streams is a major determinant of food avail-ability to stream biota. Retention of particulate matter (leaves) and dissolved nutrients (nitrogen) was studied experimentally during summer 1987 in four 300-500 m reaches of Lookout Creek, a fifth-order stream in the Cascade Mountains of Oregon. Constrained (narrow valley floor) and unconstrained (broad valley floor) reaches were selected within old-growth and second-growth riparian zones. Gingko leaves and ammonium were re-leased into the channel and retention rates were measured. Retention...

Native plant and wildlife communities along Northern California's middle Sacramento River (Red Bluff to Colusa) originally adapted to a changing pattern of erosion and deposition across a broad meander belt. The erosion-deposition process was in balance, with the river alternately building and eroding terraces. Human-induced changes to the Sacramento River, including bank protection, gravel mining, pollution, riparian vegetation removal, flow regulation, and flood control, have resulted in a number of physical and ecological effects. This study focuses on changes in bank erosion, bank...

Riparian communities established along Elder Creek, a tributary of the upper South Fork Eel River, are bounded by two frequencies of periodic flooding. The upper limit for the riparian zone occurs at bankfull stage. The lower riparian limit is associated with a more frequent stage height, called the active channel, having an exceedance probability of 11 percent on a daily average flow duration curve. Distinct tree communities occupy bankfull and active channel zones. Riparian densities (trees per meter of stream channel) along the active channel decreased with increasing channel gradient...