Moisture profiles in swelling soils

Soil Research ◽  
1974 ◽  
Vol 12 (2) ◽  
pp. 71 ◽  
Author(s):  
T Talsma
Keyword(s):  
Water Table ◽  
Water Movement ◽  
Moisture Gradient ◽  
Clay Soils ◽  
Upward Flow ◽  
Swelling Soils ◽  
Equilibrium Profile ◽  
Moisture Profiles

In situ moisture profiles are examined, in two soils of clay texture and in a loam, for the condition of equilibrium about a water table. In addition, moisture profiles during periods of approximately steady upward flow are examined in one of the soils of clay texture. Equilibrium moisture profiles in the clay soils are typical of the 'hydric' profiles which have been predicted for swelling materials. Upward water movement occurs against the moisture gradient. The equilibrium profile in the loam is typical of those observed for non-swelling materials.

Moisture equilibrium in the vertical in swelling soils. II. Applications

Soil Research ◽  
1969 ◽  
Vol 7 (2) ◽  
pp. 121 ◽  
Author(s):  
JR Philip
Keyword(s):  
Hydraulic Conductivity ◽  
Water Table ◽  
Soil Mechanics ◽  
Three Dimensional ◽  
Moisture Distribution ◽  
Specific Yield ◽  
Swelling Soils ◽  
Total Potential ◽  
Equilibrium Distributions ◽  
Moisture Profiles

The paper discusses, with the aid of calculated examples, applications in hydrology and soil mechanics of the analysis developed in Part I. Various classical concepts of groundwater hydrology fail completely for swelling soils. The distributions of saturation and of hydraulic conductivity relative to the water table differ entirely from the conventional picture. Variations in surface topography affect moisture distribution in swelling soils. The theory of this effect is developed for topographies that are not too steep and is illustrated by examples. The equilibrium distributions found would be classically interpreted as disequilibrium states persisting because of small hydraulic conductivity; but, in fact, the moisture differentials are maintained, not by a lack of conductivity, but by a lack of difference in total potential. The variation of specific yield with water table elevation and stratum thickness in swelling soils is basically different from that in non-swelling soils. The analysis of Part I is used to discuss the following topics in soil mechanics: the variation of equilibrium soil levels with water-table depth, and with water depth over the soil; the effect of surface loading on equilibrium moisture profiles and on soil levels. Extension of the analysis to two- and three-dimensional systems is treated briefly.

Remotely sensed temperature is a proxy of greenhouse gas emissions in intact and managed peatlands

2021 ◽  
Author(s):  
Ain Kull ◽  
Iuliia Burdun ◽  
Gert Veber ◽  
Oleksandr Karasov ◽  
Martin Maddison ◽  
...  
Keyword(s):  
Soil Temperature ◽  
Greenhouse Gas Emissions ◽  
Greenhouse Gas ◽  
Water Table ◽  
Ecosystem Respiration ◽  
Ghg Emissions ◽  
Remotely Sensed ◽  
Water Table Depth ◽  
Gas Emissions

<p>Besides water table depth, soil temperature is one of the main drivers of greenhouse gas (GHG) emissions in intact and managed peatlands. In this work, we evaluate the performance of remotely sensed land surface temperature (LST) as a proxy of greenhouse gas emissions in intact, drained and extracted peatlands. For this, we used chamber-measured carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) data from seven peatlands in Estonia collected during vegetation season in 2017–2020. Additionally, we used temperature and water table depth data measured in situ. We studied relationships between CO<sub>2</sub>, CH<sub>4</sub>, in-situ parameters and remotely sensed LST from Landsat 7 and 8, and MODIS Terra. Results of our study suggest that LST has stronger relationships with surface and soil temperature as well as with ecosystem respiration (R<sub>eco</sub>) over drained and extracted sites than over intact ones. Over the extracted cites the correlation between R<sub>eco</sub> CO<sub>2</sub> and LST is 0.7, and over the drained sites correlation is 0.5. In natural sites, we revealed a moderate positive relationship between LST and CO<sub>2</sub> emitted in hollows (correlation is 0.6) while it is weak in hummocks (correlation is 0.3). Our study contributes to the better understanding of relationships between greenhouse gas emissions and their remotely sensed proxies over peatlands with different management status and enables better spatial assessment of GHG emissions in drainage affected northern temperate peatlands.</p>

Monitoring of water table dynamics in peatlands with OPTRAM: Towards globally applicable algorithms in Google Earth Engine using Landsat and Sentinel-2

2021 ◽  
Author(s):  
Iuliia Burdun ◽  
Michel Bechtold ◽  
Viacheslav Komisarenko ◽  
Annalea Lohila ◽  
Elyn Humphreys ◽  
...  
Keyword(s):  
Time Series ◽  
Water Table ◽  
Input Data ◽  
Short Wave ◽  
Google Earth ◽  
Google Earth Engine ◽  
Short Wave Infrared ◽  
Northern Peatlands ◽  
Sentinel 2

<p>Fluctuations of water table depth (WTD) affect many processes in peatlands, such as vegetation development and emissions of greenhouse gases. Here, we present the OPtical TRApezoid Model (OPTRAM) as a new method for satellite-based monitoring of the temporal variation of WTD in peatlands. OPTRAM is based on the response of short-wave infrared reflectance to the vegetation water status. For five northern peatlands with long-term in-situ WTD records, and with diverse vegetation cover and hydrological regimes, we generate a suite of OPTRAM index time series using (a) different procedures to parametrise OPTRAM (peatland-specific manual vs. globally applicable automatic parametrisation in Google Earth Engine), and (b) different satellite input data (Landsat vs. Sentinel-2). The results based on the manual parametrisation of OPTRAM indicate a high correlation with in-situ WTD time-series for pixels with most suitable vegetation for OPTRAM application (mean Pearson correlation of 0.7 across sites), and we will present the performance differences when moving from a manual to an automatic procedure. Furthermore, for the overlap period of Landsat and Sentinel-2, which have different ranges and widths of short-wave infrared bands used for OPTRAM calculation, the impact of the satellite input data to OPTRAM will be analysed. Eventually, the challenge of merging different satellite missions in the derivation of OPTRAM time series will be explored as an important step towards a global application of OPTRAM for the monitoring of WTD dynamics in northern peatlands.</p>

Moisture equilibrium in the vertical in swelling soils. I. Basic theory

Soil Research ◽  
1969 ◽  
Vol 7 (2) ◽  
pp. 99 ◽  
Author(s):  
JR Philip
Keyword(s):  
Soil Mechanics ◽  
Scalar Potential ◽  
Moisture Ratio ◽  
Moisture Distribution ◽  
Soil Physics ◽  
Swelling Soils ◽  
Total Potential ◽  
Common Notion ◽  
Classical Behaviour ◽  
Equilibrium Profile

The classical methodology of the scalar potential is used to develop the theory of equilibrium moisture distribution in the vertical in swelling soils. In addition to the well-known moisture potential � and the gravitational potential -z (z being the vertical ordinate, taken positive downward), the total potential � includes a further component �, the overburden potential. It is shown that � = de/d� [P(Zo) + ?zzo] (A) where e is the void ratio, 6 is the moisture ratio, P(zJ is the load (if any) at the surface z = z,, and y is the apparent wet specific gravity. The equilibrium condition that � be constant in depth reduces to a first-order differential equation, the solutions of which represent equilibrium moisture profiles. The singular solution � = �pt for all z > zo (B) separates two distinct classes of non-singular solutions. �p, designated the pycnotatic point, is the moisture ratio at which � assumes its maximum value. Swelling soils satisfying certain conditions (which appear to be theoretically reasonable and agree with the data of soil physics and soil mechanics) possess one, and only one, pycnotatic point. In such soils, then, three distinct types of equilibrium profile occur: (i) Hydric profiles, for which the surface moisture ratio �o > �p. 6 decreases with increasing z, asymptotically approaching 8, at great depths. (ii) Pycnotaticprojiles, for which 8, = aP and equation (B) is satisfied. (iii) Xeric profiles, for which �o < �p. � increases with z, asymptotically approaching �p at great depths. The physical significance of this result is discussed with the aid of calculations for an illustrative example. The hydrology of swelling soils is entirely different in character from classical hydrological behaviour, which ignores the consequences of volume change. Contrary to a common notion, the effects of overburden potential manifest themselves right to the surface of the soil: it is not the magnitude of n, but that of d�/dz, which is important. The effect of swelling on the behaviour of the soil water may be crudely summarized as follows: Gravity operates completely in reverse to the expectations of classical theory in the 'normal' part of the hydric range; its effect diminishes to zero at the pycnotatic point; and it approaches classical behaviour at the dry end of the xeric range. Applications of the analysis to equilibrium states in hydrology and soil mechanics are treated in Part II. In later papers the concept of the overburden potential is applied to steady vertical flows and to infiltration in swelling soils.

scholarly journals A quasi-three-dimensional model for predicting rainfall-runoff processes in a forested catchment in Southern Finland

2000 ◽  
Vol 4 (1) ◽  
pp. 65-78 ◽  
Author(s):  
H. Koivusalo ◽  
T. Karvonen ◽  
A. Lepistö
Keyword(s):  
Soil Moisture ◽  
Water Table ◽  
Unsaturated Soil ◽  
Water Movement ◽  
Three Dimensional ◽  
Moisture Distribution ◽  
Richards Equation ◽  
Rainfall Runoff ◽  
Forested Catchment ◽  
Soil Moisture Distribution

Abstract. Runoff generation in a forested catchment (0.18 km2) was simulated using a quasi-three-dimensional rainfall-runoff model. The model was formulated over a finite grid where water movement was assumed to be dominantly vertical in the unsaturated soil zone and horizontal in the saturated soil. The vertical soil moisture distribution at each grid cell was calculated using a conceptual approximation to the one-dimensional Richards equation. The approximation allowed the use of a simple soil surface boundary condition and an efficient solution to the water table elevation over the finite grid. The approximation was coupled with a two-dimensional ground water model to calculate lateral soil water movement between the grid cells and exfiltration over saturated areas, where runoff was produced by the saturation-excess mechanism. Runoff was an input to a channel network, which was modelled as a nonlinear reservoir. The proposed approximation for the vertical soil moisture distribution in unsaturated soil compared well to a numerical solution of the Richards equation during shallow water table conditions, but was less satisfactory during prolonged dry periods. The simulation of daily catchment outflow was successful with the exception of underprediction of extremely high peak flows. The calculated water table depth compared satisfactorily with the measurements. An overall comparison with the earlier results of tracer studies indicated that the modelled contribution of direct rainfall/snowmelt in streamflow was higher than the isotopically traced fraction of event-water in runoff. The seasonal variation in the modelled runoff-contributing areas was similar to that in the event-water-contributing areas from the tracer analysis.

scholarly journals Numerical Study of Macropore Impact on Ponded Infiltration in Clay Soils

2013 ◽  
Vol 1 (No. 1) ◽  
pp. 16-22
Author(s):  
Kodešova Radka ◽  
Šimůnek Josef Kozak and Jiři
Keyword(s):  
Numerical Simulations ◽  
Preferential Flow ◽  
Water Movement ◽  
Numerical Study ◽  
Water Infiltration ◽  
Clay Soils ◽  
Saturated Water ◽  
Water Recharge ◽  
Considerable Impact ◽  
Hydrus 1D

The single-porosity and dual-permeability models in HYDRUS-1D (&Scaron;imůnek et al. 1998, 2003) were used to simulate variably-saturated water movement in clay soils with and without macropores. Numerical simulations of water flow for several scenarios of probable macropore compositions show a considerable impact of preferential flow on water infiltration in such soils. Preferential flow must be considered to predict water recharge in clay soils.

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