Showing papers on "Bank erosion published in 1979"

Effects of large organic material on channel form and fluvial processes

Abstract: \ SUMMARY Stream channel development in forested areas is profoundly influenced by large organic debris (logs, limbs and rootwads greater than 10 cm in diameter) in the channels. In low gradient meandering streams large organic debris enters the channel through bank erosion , mass wasting, blowdown, and collapse of trees due to ice loading. In small streams large organic debris may locally influence channel morphology and sediment transport processes because the stream may not have the competency to redistribute the debris. In larger streams flowing water may move large organic debris, concentrating it into distinct accumulations . (debris jams). Organic debris may greatly affect channel form and process by: increasing or decreasing stabilty of stream banks; influencing development of midchannel bars and short braided reaches; and faciltating, with other favourable circumstances, development of meander cutoffs. In steep gradient mountain streams organic debris may enter the channel by all the processes mentioned for low gradient streams. In addition, considerable debris may also enter the channel by way of debris avalanches or debris torrents. In small to intermediate size mountain streams with steep valley walls and little or no floodplain or flat valley floor, the effects of large organic debris on the fluvial processes and channel form may be very significant. Debris jams may locally accelerate or retard channel bed and bank erosion and/or deposition; create sites for significant sediment storage; and produce a stepped channel profile, herein referred to as ' organic stepping , which provides for variable channel morphology and flow conditions. The effed of live or dead trees anchored by rootwads into the stream bank may not only greatly retard bank erosion but also influence channel width and the development of small scour holes along the channel beneath tree roots. Once trees fall into the stream , their influence on the channel form and process may be quite different than when they were defending the banks , and, depending on thesize of the debris , size of the stream , and many other factors, their effects range from insignificant to very important.

Use of fluvial processes to minimize adverse effects of stream channelization

Abstract: Stream restoration is a means for restoring flow efficiency in streams that have become debris-choked and eroded due to the direct or indirect actions of humans. Such degraded streams are typically characterized by debris jams, severe bank erosion, overwide channels, and heavy sediment discharge brought on by altered stream regimes, land use changes or prior channelization. Stream restoration is accomplished by removing debris jams and providing fairly uniform channel cross-sections and gradients while preserving meanders, leaving as many trees as possible along stream banks, and stabilizing banks with vegetation and riprap where necessary. Economically, the cost of restoration is typically less than one-tenth of the cost of channelization. Experiments with stream restoration on Briar Creek, Gum Branch and Mallard Creek in Charlotte, North Carolina, have been extremely successful.

The possible impact of vessel wakes on bank erosion

Abstract: A summary is given of the knowledge available on vessel-generated wake, and the possible impact of this vessel wake on bank erosion. A literature survey was conducted to identify the various causes of bank erosion along waterways. A summary of the various natural effects and possible vessel effects is provided. Recession of waterway banks involves a large number of effects. The physical and chemical nature of the channel's water, the materials forming the bank, and the groundwater may increase the soil's erodibility by formerly noneroding water currents, wind waves, or vessel wakes. No computational methods exist for linking a vessel with a chosen hull shape, traveling at a chosen speed in a channel of chosen depth and chosen cross-sectional area and shape with banks of chosen height and materials, to a predicted occurrence of erosion.

Report on: Connecticut River Streambank Erosion Study, Massachusetts, New Hampshire and Vermont

Abstract: : This joint data compilation, hydrologic and geotechnical information study was assembled by the U.S. Army Corps of Engineers, NED and Colorado State University, to assess streambank erosion along 141-mile reach of Conn. River from Turners Falls Dam, Mass. to headwaters of Wilder Reservoir, Haverhill, N.H. and Wells River, VT. The report includes literature and historical review of Conn. River; existing data collection, collation and evaluation; infield short- term data collection and evaluation; definition and analysis of bank erosion causal factors; and solution alternatives. The report identifies variables causing streambank erosion; summarized and analyzes causes; distinguishes between general and upper-bank erosion; considers tractive and surface forces; and specifies common techniques used to control bank erosion. Non-structural measures also discussed. Maps, charts, tables, glossary, bibliography, and suggested protection measures are provided.

An applied geomorphological study on the selected bridge site along the brahmaputra-jamuna river in bangladesh

Abstract: Directly after the independence of Bangladesh, the government of Japan was requested to research the possibility of constructing a bridge across the Brahmaputra-Jamuna River. Constructing a bridge across the river, the most important thing to consider is the shifting of the river course and change of the banklines of the river. The shift from the Old Brahmaputra River to the present Brahmaputra-Jamuna River occurred 180 years ago. It is the fear of technical officials who govern the river in Bangladesh that the river may shift after construction of the bridge. The government of Japan was requested to fix the whole river course of the BrahmaputraJamuna River. This was, however, impossible for financial reasons because the river is both too long, and too wide. Bahadrabad, Gabargaon, Sirajganj and Nagarbari (Aricha) were selected as proposed bridge sites. The author was requested to select the most stable and suitable site among the four for the bridge based on applied geomorphological research. The main causes of the shifting of the river are remarkable crustal movement, deposition of sand, variation of discharge, and a bank completely consisting of sand. To make sure of the stability of the river at the four proposed bridge sites, the author investigated (1) the change of banklines and the location of thalwegs and prepared (2) a geomorphological map of the R. Brahmaputra-Jamuna Basin (1: 50, 000) and (3) a geomorphological map of the R. Brahmaputra-Jamuna and R. Ganges Plain (1: 1, 000, 000). (1) The author researched the change of banklines and the location of the thalweg from 1830 to the present. At the Bahadrabad site, due to the rising of the river bed, the expanding of river width and braiding of river channels are continuing. Nagarbari (Aricha) is located at the confluence between the Ganges and the Brahmaputra-Jamuna. The peak of the flood discharge of the Ganges generally occurs about one month later than that of the Brahmaputra-Jamuna. Due to the back-water, the bank erosion, change of river, and location of the thalweg are the largest among the the four proposed bridge sites. The change is smaller at the Gabargaon and Sirajganj sites. (2) The geomorphological map of the Brahmaputra-Jamuna River has been prepared by utilizing the mozaic of the aerial photographs which were taken in 1974 by the Japanese Reconnaissance Team as a base map. The author has prepared the map by utilizing the photographs and conducting field observation by boat and jeep (Fig. 5). The rivers from the border with India to Sirajganj, with a straight or meandering flow, are similar to rivers in natural levee regions. There are natural levees, back-swamp, and abandoned river courses in the alluvial fan around the Bahadrabad and Gabargaon. The author estimated that the natural levees and back-swamps were originally formed by the R. Tista, Jamuna, and Jhinai and that the alluvial fan by the Brahmaputra-Jamuna River had coverd partly the natural levees, back-swamps, and former river courses after the shifting of the Brahmaputra-Jamuna River. In the future, the area of the natural levee, back-swamp, and abandoned river courses in the fan will be buried by the future shifting of the river course. Sirajganj and Balktia (which is located across the river from Sirajganj) are situated on the old alluvial plain which was formed by the Tista, Jamuna, Jhinai, etc. more than 180 years ago. The old alluvial plain is separated from the present alluvial plain by the cliff, whose relative height is about 3 m. The narrowest point of the new plain between the old plains is 7 km in width.

Engineering geology and geomorphology of streambank erosion. report 1. eel river basin, california

Abstract: Streambank erosion, including other fluvial modifications, has occurred in the delta region of the Eel River in Humboldt County, California. Two streambank erosion control demonstration sites have been proposed in order to alleviate the loss of property and to evaluate new techniques for bank protection. The purpose of this report was to analyze, describe, and document the factors and causes of streambank erosion in the Eel River delta. The Eel River Basin occupies an area of 3625 square miles and has a length of 120 miles from the river's source on Bald Mountain in Mendocino County to its mouth in the delta region of Humboldt County. With the exception of the delta, all of the basin lies in the rugged and steep coastal ranges of California. The natural environmental conditions present in the basin were found to be conducive to high sediment yields. The conditions included steep slopes, high relief, thin soil cover, and steeply dipping, folded and fractured bedrock. Land use activities, such as grazing, timber harvesting, and road building, were also found to be contributors of high sediment yields. The causes of bank erosion in the delta are believed to be due to the influence of man's activities in an environment that is already predisposed to high sediment production.