Applied Geomorphology

Binghamton Geomorphology Symposium 11

Richard G. Craig, Jesse L. Craft

• Publisher: Routledge
• Year: 2020
• ISBN:
  9781000045895
• Edition: 1
• Topic: Geschichte
• Subtopic: Historische Geographie

This book, first published in 1982, forms the proceedings volume of the 11th Binghamton Geomorphology Symposium. Chapters cover various coastline phenomena, glacial and periglacial processes, carbonate terrains, and specific applications of geomorphic knowledge and techniques.

1

GEOMORPHIC PROCESS DATA NEEDS FOR ENVIRONMENTAL MANAGEMENT

A.G. Everett

ABSTRACT

Societal demands leading to an increase in the intensity of land use, coupled with protection of the environment are requiring increasing use of data from physical and chemical surface and near-surface processes involving the atmosphere, lithosphere, and hydrosphere. These interrelated processes are attracting increased attention from many disciplines but foremost among them should be geomorphology, for which the traditional focus has been such processes and their interrelationships.

A variety of land uses contribute to the need for process rate data: mineral and energy development; industrial, commercial, residential, and recreational development; and waste repositories, especially for the more toxic or polluting forms of wastes. To minimize the costs of maintenance during use, and, perhaps even more important, long-term maintenance over centuries, landforms of long-term stability should be designed and processes having slow rates of change should be utilized. Data for such design are not readily available in the scientific literature. Quantitative data on the short-term rates of processes under varying conditions are exceedingly scarce and are not commonly available. The more readily available estimates are for periods of thousands of years. Contrasting short-term rates for processes common to arid, temperate, and humid climates are virtually unknown. Despite several centuries of work describing landforms qualitatively, methods for rigorous quantitative analysis of process rates, including their variability, are not extensively available for application to monitoring or design problems in surface and shallow subsurface environments.

In this paper the need for such data is stressed, using various examples of slope stability and of geochemical and material transport problems associated with coal and uranium mining in arid regions of the western United States, with lignite and coal reclamation in more temperate regions such as central Texas and the eastern United States, and with recent problems associated with mining under humid tropical conditions in Papua New Guinea. Tropical environments may serve as excellent natural laboratories for certain processes that will occur under temperate and arid conditions as well as humid, but over a longer time period.

INTRODUCTION

The national objectives of many countries for increased rates of production of metallic ores and fuels, such as coal, oil shale, and uranium, coupled with concerns about environmental degradation in general and the handling of potentially toxic wastes in particular, will increase the need for careful planning and engineering of spoils, tailings, and waste material deposits. The large volume of many of these deposits creates the need for low maintenance cost, physically and hydrologically stable, man-made landforms that erode, degrade, and leach at geologically slow rates. It is desirable that such landforms be able to accommodate new uses; many, however, may need to be designed for minimal erosion and leaching rates in order to control rates of release of potentially toxic materials into the biosphere, thus precluding land uses that would require restoration to original conditions. The geographic, climatologic, and geologic settings for these man-made landforms cover the entire spectrum of conditions on the earth’s surface. Economics and feasibility will impose substantial constraints on design in both the emerging countries and those whose economies are well developed. Low-erosion-rate landforms commonly will be more expensive to construct than are those commonly used today for waste disposal, but long-term maintenance and monitoring costs, as well as possibilities of catastrophic failure, should be much reduced.

Geomorphology, having as its traditional focus the study of landforms and their processes of formation, has a major contribution to make by providing the basic design data and concepts for the creation of man-made landforms having long-term stability. At the present time, process rate data are scant for calculating stability conditions under conditions of longer-term climatic change as well as short-term meteorologic variability and the resultant physical and chemical alteration of waste pile materials.

The accepted standards for the design of stable slopes are those resulting from soils, foundation, and rock mechanics engineering tests developed under laboratory conditions. In common application, these factors do not take into consideration the variations in precipitation, permeability, soil moisture, and mineral weathering conditions that may be expected to occur during the time that waste materials are exposed to surficial processes. Empirical factors of safety commonly provide stability for a short period of time, essentially that prior to the dynamic change of geologic characteristics. The shortcoming of laboratory testing in slope design has not gone unnoticed in the soils engineering literature, as indicated by the comments of both Bishop (1966), concerning progressive failure of stiff clays, and Bjerrum (1966), on problems of slope stability resulting from weathering of clays.

Traditional engineering design factors are applied to residual slopes remaining after excavation of mines, quarries, and other varieties of cut slopes as well as to waste piles. Slopes receiving uncompacted overbank deposits can change their stability conditions both extensively and rapidly. In mining projects, the economics of removal of overburden frequently dictates that slopes be maintained in a state of slow erosion or slumping at greater-than-optimum stable slope angles. Debris from such unstable slopes is often accommodated in temporary storage on inactive benches or cleaned from slope toes at a cost less than that of stripping to create pit walls stable over a long term. After the cessation of operations, such slumping of slopes will partially fill the excavation by sapping walls and adjacent surfaces. Obviously, these processes have their own hazards both during and subsequent to the active mine operation, but they usually can be carefully managed while operations remain active and profitable. At the conclusion of operations, however, geologic factors for long-term stability are needed in order for the excavations to serve alternative land uses.

PHYSICAL AND CHEMICAL CHANGES THAT CAN AFFECT WASTE PILE PERMEABILITY

The engineering literature on the stability of rock slopes and of unconsolidated materials is growing rapidly, but much of it has not yet accounted for the dynamics of processes that will, with time, modify the original internal physical structure intended to provide long-term stability. Seed (1974) and Kealy and Busch (1979) have discussed the need to consider physical dynamic loading conditions in initial designs. They have focused both upon ruptures and liquefaction that can result from earthquakes and from “strain-induced internal movement,” citing the mine refuse dam failures at Buffalo Creek, West Virginia, in February 1972 as one familiar example of inadequate consideration. Preventive measures that they suggest include good compaction and drainage. The same factors were emphasized as well by Brawner (1979) in his review of metal mine tailings dam designs, in which he considered the problems of liquefaction of sand-size material and concluded that, with adequate density achieved by compaction, “the increased sheer strength and stability of compacted sands allows much steeper slopes and lower safety factors to be used.” Over time, modification by surface and near-surface physical and chemical processes can modify initial permeability (and particle composition) in waste materials (hence pore water pressures in piles and slopes) changing an initially sound design to one leading to failure.

Regulations of government agencies commonly call for revegetation of spoil and waste piles. The revegetation processes disrupt the initial compacted fabric by root penetration, leading to channel formation by root decay, and by alteration of alumino-silicate and carbonate components in contact with the hydrogen-ion sheath around rootlets (Loughnan 1969 has cited pHs below 4 and possibly as low as 2 adjacent to such rootlets). Revegetation of spoils will progressively modify the pore fabric by steadily increasing the volume disturbed, by root channels reoriented, or compacted by root pressure. Analogous modification of permeability and resultant soil moisture flow in natural soils has been discussed by Baker (1978) and by de Vries and Chow (1978). It is to be expected in revegetated spoil spiles and on cut slopes as well.

As noted by de Vries and Chow (1978), agricultural soils tend toward substantial horizontal homogeneity as a result both of their geologic origin, commonly as alluvial, eolian, or lacustrine deposits, and of repeated cultivation. Groenewold and Rehm (1980) indicate that spoil piles, like the forest soils studied by de Vries and Chow, tend toward both lateral and vertical inhomogeneity. Groenewold and Rehm report that, over time, both increases and decreases in waste pile hydraulic conductivity can occur. They have related these changes to compaction and to enlargement of voids. Although they have noted the relationship in spoils of highly dispersive sodic materials and piping, which may not begin for up to 5 years, chemical precipitation or small particle formation and movement in the interstices of the waste pile also may contribute to permeability modification (hence to pore water pressure distribution). In addition to interporosity chemical precipitation, another factor that may contribute to the formation of fine particles for movement within the waste pile are small particles formed by the freezing of water-saturated humic soil components. Giesy and Briese (1978) have formed fine humic particles under laboratory conditions by freezing pond water. Upon thawing the solutions and after sonic dispersal, the pond water retained increased particle sizes. Soil mulches, or other soil treatments with humic materials, and the normal accumulation of humic material with continued successful vegetation of spoils could provide the necessary humic materials to soil solutions for the generation of humic particles under freezing conditions. These particles could then move in pore spores to places where they would block permeability, leading to localized increases in pore water pressures.

Physical modification of waste pile permeability and internal pore water pressure may be a significant factor in many cases of waste pile and cut slope failure. Such physical changes, which may also be related to chemical changes, may not appear rapidly. The appearance of the same phenomenon in two places will differ in time, based on the rate at which the changes are taking place in the two locations. For those changes that occur in aqueous solutions in freely draining waste piles, humid tropical areas offer the opportunity for examination of some processes that are much accelerated. Strakhov (1967) estimated that increased leaching rates in the humid tropics increase weathering rates from seven to fourteen times that of temperate climates and, when the effects of higher average temperatures and more abundant organic matter are added to the increased rainfall, the differential in weathering rates may reach twenty to forty times. Whatever rates may best characterize the difference, it is apparent that weathering and transport processes dependent upon rainfall are much more rapid in humid tropical climates than in temperate climates. Therefore, changes in hydraulic conductivity of waste piles that influence their stability in the tropics is relevant to long-term design questions under other climatic conditions where similar processes take place under much reduced rates.

Observations by Meynink (personal communication, 1979; also Meynink 1979) on permeability changes in mine waste piles at Bougainville Copper Limited’s Panguna Mine, Papua New Guinea, indicate that under rainfall conditions of about 4 m per year, mineralogical alteration and rock particle breakdown can progress sufficie...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Contributors
• Chapter 1 Geomorphic Process Data Needs for Environmental Management
• Chapter 2 The Role of Geomorphology in the Identification and Evaluation of Natural Hazards
• Chapter 3 Landforms for Planning Use in Part of Pierce County, Washington
• Chapter 4 Geomorphology as an Aid to Hazardous Waste Facility Siting, Northeast United States
• Chapter 5 Geomorphic Manifestations of Salt Dome Stability
• Chapter 6 Slope Movements Related to Expansive Soils on the Blackland Prairie, North Central Texas
• Chapter 7 Prediction of Engineering Properties and Construction Conditions from Geomorphic Mapping in Regional Siting Studies
• Chapter 8 Criteria for Constructing Optimal Digital Terrain Models
• Chapter 9 Geomorphic Processes and Land Use Planning, South Texas Barrier Islands
• Chapter 10 Man-made Structures and Geomorphic Changes Since 1876 Along the Ohio Shore of Lake Erie
• Chapter 11 Erosion Hazards Along the Mid-Atlantic Coast
• Chapter 12 Geomorphology and Land Subsidence in Bangkok, Thailand
• Chapter 13 Land Use in Carbonate Terrain: Problems and Case Study Solutions
• Chapter 14 ERODE-A Computer Model of Drainage Basin Development Under Changing Baselevel Conditions
• Chapter 15 Morphologic and Morphometric Response to Channelization: The Case History of Big Pine Creek Ditch, Benton County, Indiana
• Chapter 16 Evaluating Aquatic Habitat Using Stream Network Structure and Streamflow Predictions