scholarly journals Groundwater erosion of coastal gullies along the Canterbury coast (New Zealand): a rapid and episodic process controlled by rainfall intensity and substrate variability

2021 ◽  
Vol 9 (1) ◽  
pp. 1-18
Author(s):  
Aaron Micallef ◽  
Remus Marchis ◽  
Nader Saadatkhah ◽  
Potpreecha Pondthai ◽  
Mark E. Everett ◽  
...  
Keyword(s):  
New Zealand ◽  
Groundwater Flow ◽  
Slope Failure ◽  
Luminescence Dating ◽  
Excess Pore Pressure ◽  
Surface Erosion ◽  
River Channels ◽  
Sandy Gravel ◽  
Groundwater Seepage ◽  
Unconsolidated Sand

Abstract. Gully formation has been associated to groundwater seepage in unconsolidated sand- to gravel-sized sediments. Our understanding of gully evolution by groundwater seepage mostly relies on experiments and numerical simulations, and these rarely take into consideration contrasts in lithology and permeability. In addition, process-based observations and detailed instrumental analyses are rare. As a result, we have a poor understanding of the temporal scale of gully formation by groundwater seepage and the influence of geological heterogeneity on their formation. This is particularly the case for coastal gullies, where the role of groundwater in their formation and evolution has rarely been assessed. We address these knowledge gaps along the Canterbury coast of the South Island (New Zealand) by integrating field observations, luminescence dating, multi-temporal unoccupied aerial vehicle and satellite data, time domain electromagnetic data and slope stability modelling. We show that gully formation is a key process shaping the sandy gravel cliffs of the Canterbury coastline. It is an episodic process associated to groundwater flow that occurs once every 227 d on average, when rainfall intensities exceed 40 mm d−1. The majority of the gullies in a study area southeast (SE) of Ashburton have undergone erosion, predominantly by elongation, during the last 11 years, with the most recent episode occurring 3 years ago. Gullies longer than 200 m are relict features formed by higher groundwater flow and surface erosion > 2 ka ago. Gullies can form at rates of up to 30 m d−1 via two processes, namely the formation of alcoves and tunnels by groundwater seepage, followed by retrogressive slope failure due to undermining and a decrease in shear strength driven by excess pore pressure development. The location of gullies is determined by the occurrence of hydraulically conductive zones, such as relict braided river channels and possibly tunnels, and of sand lenses exposed across sandy gravel cliffs. We also show that the gully planform shape is generally geometrically similar at consecutive stages of evolution. These outcomes will facilitate the reconstruction and prediction of a prevalent erosive process and overlooked geohazard along the Canterbury coastline.

scholarly journals Box canyon erosion along the Canterbury coast (New Zealand): A rapid and episodic process controlled by rainfall intensity and substrate variability

2020 ◽  
Author(s):  
Aaron Micallef ◽  
Remus Marchis ◽  
Nader Saadatkhah ◽  
Roger Clavera-Gispert ◽  
Potpreecha Pondthai ◽  
...  
Keyword(s):  
New Zealand ◽  
Slope Failure ◽  
Luminescence Dating ◽  
Excess Pore Pressure ◽  
River Channels ◽  
Sandy Gravel ◽  
Groundwater Seepage ◽  
Unconsolidated Sand ◽  
Geometrical Scaling ◽  
Pressure Development

Abstract. Box canyon formation has been associated to groundwater seepage in unconsolidated sand to gravel sized sediments. Our understanding of box canyon evolution mostly relies on experiments and numerical simulations, and these rarely take into consideration contrasts in lithology and permeability. In addition, process-based observations and detailed instrumental analyses are rare. As a result, we have a poor understanding of the temporal scale of box canyon formation and the influence of geological heterogeneity on their formation. We address these issues along the Canterbury coast of the South Island (New Zealand) by integrating field observations, optically stimulated luminescence dating, multi-temporal Unmanned Aerial Vehicle and satellite data, time-domain electromagnetic data, and slope stability and landscape evolution modelling. We show that box canyon formation is a key process shaping the sandy gravel cliffs of the Canterbury coastline. It is an episodic process associated to groundwater flow that occurs once every 227 days on average, when rainfall intensities exceed 40 mm per day. The majority of the box canyons in a study area SE of Ashburton has undergone erosion, predominantly by elongation, during the last 11 years, with the most recent episode occurring 3 years ago. The two largest box canyons have not been eroded in the last 2 ka, however. Canyons can form at rates of up to 30 m per day via two processes: the formation of alcoves and tunnels by groundwater seepage, followed by retrogressive slope failure due to undermining and a decrease in shear strength driven by excess pore pressure development. The location of box canyons is determined by the occurrence of hydraulically-conductive zones, such as relict braided river channels and possibly tunnels, and of sand lenses exposed across sandy gravel cliff. We also show that box canyon formation is best represented by a linear diffusive model and geometrical scaling.

Instability caused by a seepage impediment in layered fill slopes

2008 ◽  
Vol 45 (10) ◽  
pp. 1410-1425 ◽  
Author(s):  
Y. S. Lee ◽  
C. Y. Cheuk ◽  
M. D. Bolton
Keyword(s):  
Hydraulic Conductivity ◽  
Groundwater Flow ◽  
Slope Failure ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Friction Angle ◽  
Excess Pore Pressure ◽  
Order Of Magnitude ◽  
Numerical Parametric Study ◽  
Fill Slope

The underlying cause of loose fill slope failures in Hong Kong has been attributed to static liquefaction during heavy rainfall. A series of centrifuge model tests and numerical analyses were conducted to illustrate that instability of a fill slope inclined at approximately the internal friction angle of the soil can be triggered by confined groundwater flow due to soil layering in the fill slope. The results also showed that slope failure could occur irrespective of the density of the fill material when seepage was sufficiently impeded leading to a localised buildup of pore-water pressure in the slope. A numerical parametric study was carried out to examine the effect of variations in hydraulic conductivity in the layered fill slopes. The results showed that the excess pore pressure distribution and hence the failure mode were strongly dependent on the location of the inhomogeneous soil layers and their hydraulic properties. It was also demonstrated that layered fill slopes with spatial variation in hydraulic conductivity of as small as one order of magnitude were vulnerable to global failure under confined groundwater flow.

Groundwater flow simulation and its application in GaoSong ore field, China

2018 ◽  
Vol 10 (2) ◽  
pp. 276-284 ◽  
Author(s):  
Gang Chen ◽  
Shiguang Xu ◽  
Chunxue Liu ◽  
Lei Lu ◽  
Liang Guo
Keyword(s):  
Numerical Model ◽  
Flow Field ◽  
Groundwater Flow ◽  
Mine Water ◽  
Permeability Coefficient ◽  
Water Inrush ◽  
Seepage Field ◽  
Groundwater Seepage ◽  
Calculation Results ◽  
Groundwater Flow Field

Abstract Mine water inrush is one of the important factors threatening safe production in mines. The accurate understanding of the mine groundwater flow field can effectively reduce the hazards of mine water inrush. Numerical simulation is an important method to study the groundwater flow field. This paper numerically simulates the groundwater seepage field in the GaoSong ore field. In order to ensure the accuracy of the numerical model, the research team completed 3,724 field fissure measurements in the study area. The fracture measurement results were analyzed using the GEOFRAC method and the whole-area fracture network data were generated. On this basis, the rock mass permeability coefficient tensor of the aquifer in the study area was calculated. The tensor calculation results are used in the numerical model of groundwater flow. After calculation, the obtained numerical model can better represent the groundwater seepage field in the study area. In addition, we designed three different numerical models for calculation, mainly to explore the influence of the tensor assignment of permeability coefficient on the calculation results of water yield of the mine. The results showed that irrational fathom tensor assignment would cause a significant deviation in calculation results.

Surface erosion assessment in the South-Canterbury downlands, New Zealand using 137Cs distribution

Soil Research ◽  
1995 ◽  
Vol 33 (5) ◽  
pp. 787 ◽  
Author(s):  
LR Basher ◽  
KM Matthews ◽  
L Zhi
Keyword(s):  
New Zealand ◽  
Mean Value ◽  
Slope Position ◽  
Surface Erosion ◽  
The South ◽  
Erosion And Deposition ◽  
Erosion Rates ◽  
Land Use Types ◽  
Radionuclide Tracer

Redistribution of the radionuclide tracer 137Cs was used to examine the pattern of erosion and deposition at two sites with contrasting long-term land uses (pasture and cropping) in the South Canterbury downlands, New Zealand. There were clear differences between the two land use types in variation in 137Cs concentrations and areal activity, erosion rates and topsoil depth variability. Erosion and deposition have resulted in greater variability and lower mean levels of 137Cs areal activity under cropping (46.3 mBq cm-2) than pasture (55.0 mBq cm-2). At the cropping site, erosion and deposition roughly balanced with the mean value over all sampling sites, suggesting no net soil loss, but considerable redistribution of soil within paddocks. At the pasture site results suggested slight net deposition. There was evidence for both sheet/rill and wind erosion being important in soil redistribution. While there was no difference in mean topsoil depth between pasture and cropping, there were significant differences with slope position. At the pasture site, there was little variation of topsoil depth with slope position, except for swales which tended to be deeper, whereas at the cropping site there was considerable variation in topsoil depth with slope position. Topsoil depth was a poor indicator of erosion status.

scholarly journals Investigation of the Thermal Performance of Energy Tunnel Equipped with the Insulation Layer Considering Ventilation and Groundwater Seepage

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Guozhu Zhang ◽  
Ziming Cao ◽  
Xu Zhao ◽  
Yongli Xie ◽  
Xiaohua Liu ◽  
...  
Keyword(s):  
Heat Exchange ◽  
Groundwater Flow ◽  
Exchange Rates ◽  
Thermal Performance ◽  
Surrounding Rock ◽  
Interface Temperature ◽  
Insulation Layer ◽  
Groundwater Seepage ◽  
Ground Heat Exchangers ◽  
Reduction Effect

The insulation layer is usually installed in the tunnel structure, whereas the influence of the insulation layer on the thermal behavior of energy tunnel ground heat exchangers (GHEs) is rarely investigated. The model tests were performed in this study to evaluate the heat transfer potential of the energy tunnel with the insulation layer under ventilation and groundwater seepage. The results can be obtained as follows: first, the fluctuations of air temperature and surrounding rock temperature at different locations are relevant to insulation layer, ventilation, and groundwater seepage. Second, the reduction effect of ventilation on the interface temperature of tunnel lining and surrounding rock is alleviated when using an insulation layer, and the interface temperature at upstream section of groundwater seepage is more easily affected by the energy tunnel GHEs. Third, the variation range of ground temperature is wider at the downstream section of groundwater flow. Moreover, the heat exchange rates of tunnel without the insulation layer improve by 5.82% and 6.45% with increasing wind speed at two groundwater flow velocities of 1 × 10 − 4 and 5 × 10 − 4  m/s, and there are only 2.03% and 0.77% enhancements of heat exchange rates by ventilation for the tunnel with the insulation layer. However, the thermal performance of the energy tunnel improved by groundwater is less relevant to the existence of the insulation layer. The relevant findings can provide an effective guidance for the following research and design of the energy tunnel.

scholarly journals Numerical estimation of fracture network permeability based on GEOFRAC model for groundwater modeling in a tin mine

2018 ◽  
Vol 10 (2) ◽  
pp. 243-248
Author(s):  
Lei Lu ◽  
Chunxue Liu ◽  
Gang Chen ◽  
Liang Guo
Keyword(s):  
Groundwater Flow ◽  
Slope Failure ◽  
Groundwater Modeling ◽  
Flow Simulation ◽  
Fracture Network ◽  
Fracture Plane ◽  
Two Dimensional ◽  
Mining Operations ◽  
Sample Data ◽  
Ore Distribution

Abstract Numerous geological research studies and mining operations have proved that fracture is one of the important factors controlling groundwater flow, mineralization, and ore distribution in metallic deposits. Most current approaches to groundwater flow simulation of naturally fractured media rely on the calculation of equivalent permeability tensors from a discrete fracture network (DFN). This study is aimed at developing a rational two-dimensional DFN by GEOFRAC, a geostatistical method of fracture direction and locations of sample data from a tin mine in the Gaosong area, Gejiu city, southwest China, and utilizing 3,724 outcrop fractures sampled on the ground of mountain Gaosong. Principal inputs of the DFN are density, direction, and continuity of disks that constitute a fracture plane. Fractures simulated by GEOFRAC were validated in that their directions corresponded well with those of the sample fractures. The permeability tensor of each modeling grid was then calculated based on the fracture network constructed. The results showed that GEOFRAC is valuable for two-dimensional DFN modeling in mines and other fracture-controlled geological phenomena, such as groundwater flow and slope failure.

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