Surface Drainage Patterns Research Articles

Locating potential borehole sites in a discordant flow regime in the Chalk aquifer at Lulworth using integrated geophysical surveys

Summary Groundwater flow in the Chalk Aquifer at Lulworth is discordant with the surface drainage pattern as a result of flow reversal consequent upon coastal breaching of the aquifer. Siting of boreholes for water supply is thus made difficult, especially since flow is confined to very narrow zones. The use of geophysical techniques has enabled such zones to be identified with varying degrees of certainty. It is important not to place too much reliance on a single technique and to integrate such surveys into an overall appreciation of the evolution of the groundwater flow regime in order to obtain maximum benefits.

The Inversion Wind Pattern over West Antarctica

Abstract The surface windfield over the gently sloping interior ice fields of Antarctica is characterized by a high degree of persistence in terms of both direction and speed. The forcing of the surface wind is due primarily to the radiational cooling of the air adjacent to the sloping terrain. The representativeness of a simple diagnostic equation system in inferring the surface winds from a knowledge of terrain slope and temperature inversion structure is examined. Results suggest at least qualitatively accurate surface drainage patterns over the Antarctic continent are possible using this technique. A wintertime surface wind simulation for West Antarctica has been generated based on an accurate ice topography map. Close agreement is seen between the simulated surface windfield with field observations and sastrugi orientations. Implications of the simulation are discussed.

Piezometric Observations of Water Pressure at the Bed of Swiss Glaciers

AbstractA technique for drilling deep holes with a hot-water jet has been developed in recent years at our institute (Iken and others, [1977]). The holes have served to investigate the water pressure at the bed of various Swiss glaciers since 1973. Drainage occurred naturally in rare cases when the drill reached the bed, but more often it was necessary to use explosives first, probably because the drill was stopped short of the bottom of the glacier by rock inclusions in the ice. In order to record piezometric water pressure over an extended period of time it was necessary that water was draining fairly continuously into the hole, otherwise the water level dropped eventually to a great depth when the weather turned cold, whereupon the holes closed off. By suddenly shutting off the water supply to a hole and observing the lowering of the water level with time some information on the channel characteristics has been obtained. In many cases there was little change of level, indicating that such a hole gives almost the true pressure head of the subglacial drainage system.Our efforts have so far been concentrated on flat tongues of fair size over 100 m thick, the distance from the uppermost hole to the terminus ranging from about 1 to 4.5 km. The main characteristic of the water pressure is a very large diurnal variation of the order of 100 m and more. The mean pressure generally rises and falls in times of high and low water supply, respectively, but re-adjusts to approximately the original level within a few days. Mean levels are higher early in the melt season than later, and the amplitude of the diurnal variation has a tendency to increase with time, but also shows strong short-term modulations depending on the water supply. From observations on moulins and a hole which had remained connected to the bed from the previous year it seems likely that at the beginning of the melt season the water pressure at the bed may become as large as or larger than the ice pressure.On Gornergletscher a record of water pressures has been obtained during the drainage of Gornersee, an ice-dammed lake at the confluence of the two main branches of the glacier. Levels stayed high day and night in the piezometer holes, which were located off to the side of where the main drainage channel was suspected to pass through. The surface drainage pattern was affected over a large area of the glacier. These two observations indicate that during the drainage of the lake some sort of sheet flow must have occurred. The surface velocity of the glacier roughly doubled during that time, but no lifting-up of the ice was observed within the accuracy of the survey. On one occasion on Glacier de Breney the main channel must have been blocked temporarily between an upper area, where the water level was rising simultaneously in three piezometer holes, and an area further down-glacier, where the holes were not affected.

Piezometric Observations of Water Pressure at the Bed of Swiss Glaciers

Abstract A technique for drilling deep holes with a hot-water jet has been developed in recent years at our institute (Iken and others, [1977]). The holes have served to investigate the water pressure at the bed of various Swiss glaciers since 1973. Drainage occurred naturally in rare cases when the drill reached the bed, but more often it was necessary to use explosives first, probably because the drill was stopped short of the bottom of the glacier by rock inclusions in the ice. In order to record piezometric water pressure over an extended period of time it was necessary that water was draining fairly continuously into the hole, otherwise the water level dropped eventually to a great depth when the weather turned cold, whereupon the holes closed off. By suddenly shutting off the water supply to a hole and observing the lowering of the water level with time some information on the channel characteristics has been obtained. In many cases there was little change of level, indicating that such a hole gives almost the true pressure head of the subglacial drainage system. Our efforts have so far been concentrated on flat tongues of fair size over 100 m thick, the distance from the uppermost hole to the terminus ranging from about 1 to 4.5 km. The main characteristic of the water pressure is a very large diurnal variation of the order of 100 m and more. The mean pressure generally rises and falls in times of high and low water supply, respectively, but re-adjusts to approximately the original level within a few days. Mean levels are higher early in the melt season than later, and the amplitude of the diurnal variation has a tendency to increase with time, but also shows strong short-term modulations depending on the water supply. From observations on moulins and a hole which had remained connected to the bed from the previous year it seems likely that at the beginning of the melt season the water pressure at the bed may become as large as or larger than the ice pressure. On Gornergletscher a record of water pressures has been obtained during the drainage of Gornersee, an ice-dammed lake at the confluence of the two main branches of the glacier. Levels stayed high day and night in the piezometer holes, which were located off to the side of where the main drainage channel was suspected to pass through. The surface drainage pattern was affected over a large area of the glacier. These two observations indicate that during the drainage of the lake some sort of sheet flow must have occurred. The surface velocity of the glacier roughly doubled during that time, but no lifting-up of the ice was observed within the accuracy of the survey. On one occasion on Glacier de Breney the main channel must have been blocked temporarily between an upper area, where the water level was rising simultaneously in three piezometer holes, and an area further down-glacier, where the holes were not affected.

Runoff from Watershed Models

Iconic watershed models were used under a rainfall simulator to determine the nature of the hydrograph response to depth of surface storage medium, model slope, drainage pattern, and drainage density. Tests were made with carefully selected sponge material to represent soil under varying degrees of saturation. Results show, as reported elsewhere, that geomorphic features have little or no effect on the hydrograph when there is surficial saturation, but that under less than saturated conditions these watershed characteristics do materially affect hydrograph parameters.

Glacier Drainage Connected with Ice Structures

Systematic observations on Mikkaglaciären in northern Sweden are presented and a general discussion is given concerning drainage connected with structures in the upper layer of a glacier. The basic conditions (surface drainage and structural pattern) for this drainage are first analyzed. A series of observations on “drainage structures” during a five-year period is presented and reproduced on a map (Fig. 7). Descriptions and comments are given as to the formation and further development of observed glacier mills and related features, with regard to local environmental characteristics and to the time factor involved. The development is studied also in its correlation to the transfer and rotation of the initial, mill-localizing cracks, and as regards the mutual relationships between neighbouring mill units. Different possibilities of recognizing sub-surface inter-connections between mills are commented on, and an obliquely transverse deflection of the upper parts of sub-surface drainage courses is pointed out. This drainage characteristic leads to a consideration of the most probable, near-lateral location of the further reaches of internal drainage courses.

Some Geomorphological Implications of Deep Weathering Patterns in Crystalline Rocks in Nigeria

THE PHENOMENON of deep weathering has received frequent discussion in papers concerned with the geomorphology of terrains developed on crystalline rocks, yet few of these studies show actual depths of weathering except for occasional, isolated locations. This absence of quantitative information obviously weakens arguments based upon the premise that deep weathering occurs widely within a given area or displays particular relationships with surface relief, drainage patterns or individual landforms. This deficiency is explained by the paucity of existing records and the difficulty of obtaining additional data where weathering depths commonly exceed fifty feet. Drilling and portable seismographs are both commonly used by civil engineersl, and the information used in this paper is derived from these sources. It is recognized that such data have certain inherent inadequacies. First the sites are chosen because they appear from surface considerations to be suitable for the ultimate purpose of the project. Most surveys of this kind in Nigeria have been undertaken to determine the suitability of sites for dam foundations. As a result the sites selected are mostly well-defined valleys which usually display frequent fresh rock outcrops. They are not therefore located in areas where weathering depths would be expected to be great. In spite of this limitation there is sufficient variety of site to make the profiles representative of more than one type of terrain. The second difficulty is the lack of uniformity in the terms used to describe the various zones of the weathering profile. Furthermore, subdivision of the profile on the basis of seismic information is not often very accurate. For most of the profiles presented in this study emphasis has therefore been placed only on the recognition of the sound rock line or basal surface of weathering, but there are difficulties even here, for the transition from weathered to fresh rock varies greatly in its characteristics from one borehole to another. There is also the possibility that the upper part of the profile may contain transported material, either sandy wash similar to that recognized for instance by R. V. Ruhe2 or wind blown dust that is well known from Northern Nigeria. Both J. D. Falconer3 and more recently J. Dresch4 have called attention to the role of alluviation in depressions on the interior plains of West Africa. However, it is not thought likely that any serious errors, resulting from the inclusion of transported materials under the heading of in situ weathering products, have been incorporated into the profiles to be described. Seismic traverse information which may be ambiguous in this respect, has been included only from the humid south of Nigeria, where alluvial infilling of the kind envisaged above does not appear to have taken place, and from the Niger valley near Bussa, where a large amount of confirmatory drilling information is