Development of Unstable Flow and Reduced Hydraulic Conductivity due to Water Repellence and Restricted Drainage
23
Citation
64
Reference
10
Related Paper
Citation Trend
Abstract:
The effect of water repellence and antecedent soil moisture on wetting front stability and infiltration rate are reported for a seasonally water repellent topsoil. The effect of water repellence on infiltration was determined by comparing the in situ infiltration of water to that of a 7M ethanol solution. Wetting front stability was measured during infiltration of water into repacked, wettable and water repellent soils, within a Hele‐Shaw chamber. Water repellence restricted in situ movement of water through large macropores (>500 μm), which decreased intrinsic permeability by 1 to 2 orders of magnitude. In repacked soils, water repellence caused the development of unstable wetting fronts and reduced infiltration from 240 mm h − 1 to 101.7 mm h − 1 . Infiltration into wettable soils at moisture contents near field capacity was expected to result in rapid infiltration and stable wetting fronts. However in repacked soils, wetting front instability developed, and infiltration rates were 190% lower when air and/or water movement through the base of the chamber was restricted. Infiltration into in situ soil was also slower at high antecedent soil moisture. The hydraulic conductivity of the 7M ethanol solution decreased significantly from 112.3 mm h − 1 in dry water repellent conditions, to 35.6 mm h − 1 in wettable soils at high antecedent moisture contents. Consequently the previously reported development of wetting front instability and reduced infiltration into in situ wettable soils at high moisture contents were confirmed and attributed to difficulty displacing existing soil water during infiltration of new water.Keywords:
Infiltration (HVAC)
Water repellent
Macropore
Pedotransfer function
Outflow
Water retention curve
Cite
Citations (14)
Traditional approaches for estimating soil hydraulic parameters (such as the RETC code) perform well when experimental data for both the retention curve and hydraulic conductivity function are available; however, unsaturated hydraulic conductivity data are often unavailable. The objective of this work was to develop an approach to estimate robust soil hydraulic parameters from water retention curve data alone. The proposed approach, called the Multiobjective Retention Curve Estimator (MORE), is based on the Multiobjective Shuffled Complex Evolution Metropolis (MOSCEM‐UA) algorithm and estimates an optimal parameter set by simultaneously minimizing two objective functions each representing water content and relative unsaturated hydraulic conductivity residuals. To address the lack of observed unsaturated hydraulic conductivity data, MORE transforms both predicted and observed water contents into the hydraulic conductivity space using a pore‐size distribution model (e.g., the Mualem model) and also optimizes the soil hydraulic parameters in this fictitious space. We applied MORE to two cases. In the first case, MORE was used to estimate soil parameters using only retention curve data for 12 random soils selected from the UNSODA database. While the soil hydraulic parameters estimated using RETC and MORE fit the retention curve similarly, the MORE approach consistently decreased the error in fitting unsaturated hydraulic conductivities by as much as 5% compared with RETC. The second case involved using the parameters fitted using the MORE and RETC approaches to model a field‐scale experiment. Compared with RETC, the error in predicted water contents decreased by 25% using parameters predicted by MORE. The MORE approach was shown to fit robust soil hydraulic parameters; however, the approach is relatively slower and more time consuming than RETC.
Water retention curve
Pedotransfer function
Cite
Citations (19)
Abstract Preferential movement of surface‐applied chemicals to the groundwater has resulted in a great need to physically model the movement of water into and through the soil media. The objective of this study was to develop equations capable of predicting both matrix and macropore saturated conductivity and to relate the equation parameters to readily available soil properties. Equations for predicting the matrix and macropore saturated conductivity were developed by coupling fractal processes with the Marshall saturated conductivity formulation. The equation uses matrix and macropore porosity, maximum pore radius, and number of pore classes. Prediction equations were developed relating the number of pore classes and maximum pore radius to soil properties. The modified Marshall saturated hydraulic conductivity equation appears to provide reasonable estimates of matrix and macropore saturated conductivity and is applicable to a wide range of soil textures.
Macropore
Richards equation
Matrix (chemical analysis)
Cite
Citations (86)
Many soils worldwide show water repellency to some degree. Soil water repellency (SWR) is known to alter hydraulic processes. Particularly in water‐repellent soils a decreased water infiltration rate can be observed. In this case soil hydraulic properties, like the hydraulic conductivity, not only are a result of the soil's pore system but also depend on the physicochemical properties of the pore surfaces (water repellency). Ethanol as a completely wetting liquid is not influenced by the soil's water repellency. In this study we introduce the concept of intrinsic soil hydraulic properties, that is, the hydraulic properties that are only dependent on the porous system and independent of its surface properties. We used the concept of intrinsic permeability, originally developed for saturated conditions. The effect of different liquid surface tensions of water and ethanol, important under unsaturated conditions, was incorporated using a correction factor for the matric potential. Retention and saturated and unsaturated liquid conductivity of water and ethanol were systematically measured in sand and glass‐bead porous media with different wettabilites. Results showed no difference between the intrinsic hydraulic properties (measured with ethanol) and the hydraulic properties (measured with water) in fully wettable porous media. In water‐repellent porous media, intrinsic hydraulic properties deviate from measured hydraulic properties. Measurements further showed that the influence of soil water repellency on hydraulic conductivity and retention of water can be predicted as a function of the macroscopic contact angle (CA) in these model substrates. In summary, at least for well‐defined substrates such as sands, we suggest measuring the hydraulic conductivity and intrinsic liquid retention of the pore system with ethanol as a standard procedure.
Infiltration (HVAC)
Cite
Citations (30)