How Some Trees Survive the Summer Dry Season

Abstract. Forests are thought to play an important role in the regional dynamics of the West African monsoon, through their capacity to extract water from a permanent and deep groundwater table to the atmosphere even during the dry season. It should be the case for riparian forests too, as these streambank forests are key landscape elements in Sudanian West Africa. The interplay of riparian forest and groundwater in the local hydrodynamics was investigated, by quantifying their contribution to the water balance. Field observations from a comprehensively instrumented hillslope in northern Benin were used. Particular attention was paid to measurements of actual evapotranspiration, soil water and deep groundwater levels. A vertical 2-D hydrological modelling approach using the Hydrus software was used as a testing tool to understand the interactions between the riparian area and the groundwater. The model was calibrated and evaluated using a multi-criteria approach (reference simulation). A virtual experiment, including three other simulations, was designed (no forest, no groundwater, neither forest nor groundwater). The model correctly simulated the hydrodynamics of the hillslope regarding vadose zone dynamics, deep groundwater fluctuation and actual evapotranspiration dynamics. The virtual experiment showed that the riparian forest transpiration depleted the deep groundwater table level and disconnected it from the river, which is consistent with the observations. The riparian forest and the deep groundwater table actually form an interacting transpiration system: the high transpiration rate in the riparian area was shown to be due to the existence of the water table, supplied by downslope lateral water flows within the hillslope soil layer. The simulated riparian transpiration rate was practically steady all year long, around 7.6 mm d−1. This rate lies within high-end values of similar study results. The riparian forest as simulated here contributes to 37% of the annual hillslope transpiration, and reaches 57% in the dry season, whereas it only covers 5% of the hillslope area.

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Effectiveness Analysis of Canal Blocking in Sub-peatland Hydrological Unit 5 and 6 Kahayan Sebangau, Central Kalimantan, Indonesia

Journal of Engineering and Technological Sciences ◽

10.5614/j.eng.technol.sci.2021.53.2.5 ◽

2021 ◽

Vol 53 (2) ◽

pp. 210205

Author(s):

Yadi Suryadi ◽

Indratmo Soekarno ◽

Ivan Aliyatul Humam

Keyword(s):

Significant Influence ◽

Satisfactory Result ◽

Good Condition ◽

Ground Level ◽

Dry Season ◽

Groundwater Table ◽

Central Kalimantan ◽

Effectiveness Analysis ◽

Below Ground ◽

Groundwater Rise

The height of canal blocking has a significant influence on re-wetting peatland, depending on the canal’s distance. An effective canal in good condition has to raise the groundwater table to -0.4 m below ground level according to the Indonesian Ministry of Environment and Forestry (MENLHK). The effectiveness of different canal blockings was modeled by Freewat software with variation of canal distance (200 m, 250 m, 300 m, 350 m, and 400 m) and blocking height (0.2 m, 0.3 m, 0.4 m, 0.5 m, 0.6 m). This simulation was carried out using recharge and evapotranspiration data covering 20 years. The input of the conductivity value was done using 50 m/day according to the calibration. From the modeling, 0.6 m high canal blockings give a satisfactory result at every canal distance. The study took place during the annual dry season, when recharge was almost zero and average evapotranspiration was 6 mm/day. Adjusting the canal blocking to a maximum of 0.6 m and the canal distance to 400 m, the groundwater table slowly rose 0.38 m and it took 30 days to reach full-re-wetting capacity. This study revealed that the effectiveness of canal blocking is directly related to evapotranspiration and recharge, which has a positive correlation with the groundwater rise and the re-wetting period.

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Assessing the Effects of Rainfall Intensity and Hydraulic Conductivity on Riverbank Stability

Water ◽

10.3390/w11040741 ◽

2019 ◽

Vol 11 (4) ◽

pp. 741

Author(s):

Toan Thi Duong ◽

Duc Minh Do ◽

Kazuya Yasuhara

Keyword(s):

Hydraulic Conductivity ◽

Unsaturated Soil ◽

Rainfall Intensity ◽

Groundwater Table ◽

Wetting Front ◽

Soil Hydraulic Conductivity ◽

Rainwater Infiltration ◽

Soil Hydraulic ◽

Transient Seepage ◽

Riverbank Stability

Riverbank failure often occurs in the rainy season, with effects from some main processes such as rainfall infiltration, the fluctuation of the river water level and groundwater table, and the deformation of transient seepage. This paper has the objective of clarifying the effects of soil hydraulic conductivity and rainfall intensity on riverbank stability using numerical analysis with the GeoSlope program. The initial saturation condition is first indicated as the main factor affecting riverbank stability. Analyzing high-saturation conditions, the obtained result can be used to build an understanding of the mechanics of riverbank stability and the effect of both the rainfall intensity and soil hydraulic conductivity. Firstly, the rainfall intensity is lower than the soil hydraulic conductivity; the factor of safety (FOS) reduces with changes in the groundwater table, which is a result of rainwater infiltration and unsteady state flow through the unsaturated soil. Secondly, the rainfall intensity is slightly higher than the soil hydraulic conductivity, the groundwater table rises slowly, and the FOS decreases with both changes in the wetting front and groundwater table. Thirdly, the rainfall intensity is much higher than the soil hydraulic conductivity, and the FOS decreases dominantly by the wetting front and pond loading area. Finally, in cases with no pond, the FOS reduces when the rainfall intensity is lower than hydraulic conductivity. With low hydraulic conductivity, the wetting front is on a shallow surface and descends very slowly. The decreasing of FOS is only due to transient seepage changes of the unsaturated soil properties by losing soil suction and shear strength. These obtained results not only build a clearer understanding of the filtration mechanics but also provide a helpful reference for riverbank protection.

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Migration and Transformation of Chromium in Unsaturated Soil during Groundwater Table Fluctuations Induced by Rainfall

Journal of Hazardous Materials ◽

10.1016/j.jhazmat.2021.126229 ◽

2021 ◽

pp. 126229

Author(s):

Yaqiang Wei ◽

Xiaoyun Xu ◽

Ling Zhao ◽

Xiang Chen ◽

Hao Qiu ◽

...

Keyword(s):

Unsaturated Soil ◽

Groundwater Table

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Natural Attenuation of Volatile Hydrocarbons in Unsaturated Soil Zone

Journal of Agricultural and Marine Sciences [JAMS] ◽

10.24200/jams.vol7iss2pp9-15 ◽

2002 ◽

Vol 7 (2) ◽

pp. 9

Author(s):

P. Grathwohl ◽

U. Maier

Keyword(s):

Unsaturated Soil ◽

Arid Regions ◽

Groundwater Table ◽

Transfer Rates ◽

Volatile Hydrocarbons ◽

Soil Zone ◽

Outdoor Test ◽

The Individual ◽

Contaminant Transfer ◽

Surface And Groundwater

Scenario-specific numerical simulations were performed in order to assess the diffusive spreading of volatile fuel constituents and their biodegradation in the unsaturated soil zone. This is especially important in arid regions where the groundwater table is far below the surface and groundwater recharge is limited. The model results compare well with data from a controlled outdoor test with an emplaced source of kerosene. Modelling results illustrate that the overall biodegradation rates depend mainly on properties of the fuel constituents such as Henry’s Law constant, on the individual degradation rate constants, the soil water content and temperature. The contaminant transfer rates into groundwater can be determined provided the spreading processes in the unsaturated zone are understood.

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Riparian forest and permanent groundwater: a key coupling for balancing the hillslope water budget in Sudanian West Africa

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-10-5643-2013 ◽

2013 ◽

Vol 10 (5) ◽

pp. 5643-5686

Author(s):

A. Richard ◽

S. Galle ◽

M. Descloitres ◽

J. M. Cohard ◽

J. P. Vandervaere ◽

...

Keyword(s):

Soil Moisture ◽

Water Balance ◽

Riparian Forest ◽

Dry Season ◽

Groundwater Table ◽

Riparian Forests ◽

Actual Evapotranspiration ◽

Anthropogenic Pressure ◽

Deep Groundwater ◽

African Monsoon

Abstract. Forests are thought to play an important role in the regional dynamics of the West African monsoon, through their capacity to extract water from permanent aquifers located deep in the soil and pump it into the atmosphere even during the dry season. This is especially true for riparian forests located at the bottom of the hillslopes. This coupling between the riparian forests and the permanent aquifers is investigated, looking for quantifying its contribution to the catchment water balance. To this end, use is made of the observations available from a comprehensively instrumented hillslope through the framework of the AMMA-CATCH (African Monsoon Multidisciplinary Analysis – Coupling the Tropical Atmosphere and the Hydrological Cycle) observing system. Attention is paid to measurements of actual evapotranspiration, soil moisture and deep groundwater level. A vertical 2-D approach is followed using the physically-based Hydrus 2-D model in order to simulate the hillslope hydrodynamics, the model being calibrated and evaluated through a multi-criteria approach. The model correctly simulates the hydrodynamics of the hillslope as far as soil moisture dynamics, deep groundwater fluctuation and actual evapotranspiration dynamics are concerned. In particular, the model is able to reproduce the observed hydraulic disconnection between the deep permanent groundwater table and the river. A virtual experiment shows that the riparian forest depletes the deep groundwater table level through transpiration occurring throughout the year so that the permanent aquifer and the river are not connected. Moreover the riparian forest and the deep groundwater table form a coupled transpiration system: the riparian forest transpiration is due to the water redistribution at the hillslope scale feeding the deep groundwater through lateral saturated flow. The annual cycle of the transpiration origin is also quantified. The riparian forest which covers only 5% of the hillslope generates 37% of the annual transpiration, this proportion reaching 57% during the dry season. In a region of intense anthropogenic pressure, forest clearing and its replacement by cropping could impact significantly the water balance at catchment scale with a possible feedback on the regional monsoon dynamics.

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Assessment of landslide behaviour in colluvium deposit at Doi Chang, Thailand

Scientific Reports ◽

10.1038/s41598-021-02363-3 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Suttisak Soralump ◽

Avishek Shrestha ◽

Worawat Thowiwat ◽

Ramatre Sukjaroen ◽

Thapthai Chaithong ◽

...

Keyword(s):

Rainy Season ◽

Ground Surface ◽

Site Investigation ◽

Dry Season ◽

Groundwater Table ◽

Slope Movement ◽

Large Area ◽

Wet Season ◽

Movement Rate ◽

Infinite Slope

AbstractThe paper presents the case study of the recurrent slope movement in colluvium deposits at Doi Chang, Thailand. A thorough site investigation confirmed the slope movement rate corresponding to slow creep during dry season, while in the rainy season, its velocity remarkably increased. Despite frequent repair, the movement rate was sufficient to result in the recurrent damage of infrastructures like roads and buildings, causing economic loss and public concerns. Furthermore, surface mapping revealed that the hill's topography led to the concentration of flowing water in a particular area. This resulted in a high level of groundwater table, especially during the rainy season. The inclinometer installed in that area suggested an average movement rate of 20.5 mm/month in the wet season. In contrast, during the dry season, it was limited within 2 mm/month, indicating that the increase in the rate of slope movement in the colluvium deposit was primarily due to the rising groundwater table. Field and laboratory tests were conducted to determine the properties of the colluvium deposit. Landslide susceptibility assessment was performed using infinite slope model and later integrated with GIS to evaluate the factor of safety (FS) over a large area. The FS decreased below 1 when the groundwater level rose to 0.3 cm below the ground surface, and using GIS, based on infinite slope model, the potential risk zone were delineated.

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Evaluation on slope stability of unsaturated soils

Journal of Nepal Geological Society ◽

10.3126/jngs.v22i0.32303 ◽

2000 ◽

Vol 22 ◽

Author(s):

L. J. Wang ◽

M. Zhang

Keyword(s):

Unsaturated Soil ◽

Unsaturated Soils ◽

Pore Water Pressure ◽

Limit Equilibrium ◽

Water Pressure ◽

Matric Suction ◽

Groundwater Table ◽

Degree Of Saturation ◽

Engineering Properties ◽

Soil Slopes

In drought-prone and semiarid areas, the groundwater table is deep and the soils are at an unsaturated state because of evaporation or transpiration. The negative pore water pressure or matric suction (ua-uw) is an important property of unsaturated soils that are situated above the groundwater table. In the conditions of rainfall, ground seepage, or drainpipe leakage, the matric suction will decrease with the increase of the degree of saturation, and the soils will lose their part of shear strength, which is the main reason why many unsaturated soil slopes become unstable. This paper discusses the engineering properties of unsaturated soils. Following the limit equilibrium principle, the unsaturated soil slopes are evaluated by applying the slice method.

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