Geomorphic Principles, Stability and Reclamation Planning

Abstract

Geomorphology is the study of the earth's surface, its processes, the magnitude and frequency of those processes and the relationship between geomorphic processes and landform.Rate is a fundamental concept in geomorphology and rates vary greatly in time and space. Stability, in a geomorphic sense, is a state in which slight perturbations of the landscape are damped to return to the original state and do not lead to a progression.toward a new equilibrium. Landscapes tend toward stability.Hillslopes are the inclined part of the land surface and are the product of hillslope processes. For natural systems, in the short-term, hillslope form governs process, but in the long-term, process determines form. In reclamation situations, the form is determined by the backfill and grading plan, and therefore, so are the dominant processes.Two processes of primary importance for reclaimed lands are mass-movement and erosion.In general, reclamation activities that reduce erosion also reduce mass-movement, and therefore, this discussion focuses on controlling erosion. Gradient is the most important factor in hillslope erosion rates. Hillslope length i.s also significant, as are hillSlope longitudinal and plan form.In general, with respect to control of erosion rate, reclaimed hillslopes should have low gradients, short lengths and a diversity of hillslope forms.In ci'rcumstances where this·· is not· easily achieved, longitudinal ·and· plan form, · and height may be adj l!S1;ed. · Stream channels receive flow and sediment from hillslopes and convey them to the basin outlet. Channel morphology is a function of the amount of water and sediment carried by the channel and the character of the bed and bank materials. Design criteria for channels can be determined by permissible velocity, allowable tractive stress, or geomorphichydraulic t·echniques.Reclaimed stream channels must be capable of transporting background levels of water and sediment discharge in order to provide a smooth transition between reclaimed and undisturbed channels.Hillslopes ·and channels are integrated to form a channel network and drainage basin. Quantitative analysis of drainage basins shows that basin morphology and erosion rate is related to climate, lithology, and relief. Mining and reclamation may alter lithologic controls or relief suggesting that equilibrium drainage basin morphology will be altered by surface mining. Quantitative relationships between basin morphology and basin relief and lithologic ·characteristics can be used to design postmining equilibrium drainage basins based on the changes in relief and materials characteristics brought about by mining.