THE EFFECTS OF ROCK FRAGMENT SHAPES AND POSITIONS ON MODELED HYDRAULIC CONDUCTIVITIES OF STONY SOILS

Transcription

1 5 th International Conference 'Hydrus Software Applications to Subsurface Flow and Contaminant Transport Problems' THE EFFECTS OF ROCK FRAGMENT SHAPES AND POSITIONS ON MODELED HYDRAULIC CONDUCTIVITIES OF STONY SOILS Hana Hlaváčiková, Viliam Novák, Jirka Šimůnek, Ladislav Holko, Zdeněk Kostka, and Michal Danko Institute of Hydrology, Slovak Academy of Sciences University of California Riverside March 30-31, Prague 2017

2 Motivation In Slovakia, there are about 80% of forest and 47% of agricultural soils reffered to as stony soils (Šály,1978; Hraško and Bedrna, 1988) Despite this there is not available the standardized methodology: 1/ how to estimate hydrophysical properties of stony soils, and 2/ how to incorporate the influence of rock fragments into soil water flow modeling In water balance modeling or water storage estimations rock fragments are often neglected

3 Specific features of stony soils Fine soil Two different components: Rock fragments + Therefore enough large REV is needed for measurements which may be m 3 and larger Important characteristic of stony soils: SOIL STONINESS Relative volume or relative mass of rock fragments

4 The Jalovecký Creek catchment in the Western Tatra Mountains, northern Slovakia, central Europe AREA: 22,2 km 2 Slovakia The Jalovecký Creeck Catchment

5 REPRESENTATIVE SOIL PROFILES 5 - JALOVECKA VALLEY.840 m a.s.l., Cambisol Slope 70% FOREST 2 - ČERVENEC -OPEN AREA m a.s.l., Rendzic Leptosols Slope 10% MEADOW 3 - ČERVENEC FOREST m a.s.l., Cambisol Slope 24% 1- POD LYSCOM m a.s.l., Cambisol Slope 40% FOREST FOREST 4 - TOKARINY 700 m a.s.l., Fluvisol MEADOW

6 SOIL STONINESS (R v ) Relative volume of rock fragments Large spatial and also profile variability

7 THE INFLUENCE OF SHAPE AND DISTRIBUTION OF ROCK FRAGMENTS IN STONY SOILS ON SATURATED HYDRAULIC CONDUCTIVITY The main objectives The influence of stoniness, different shapes, position (vertical / horizontal) and distribution (regular / irregular) of RF on K s b Verification of available equations for K s b calculation HYDRUS-2D/3D model (Šimunek et al., 2008)

8 The main effects of RF on Ks 1/ RF reduce the effective cross sectional area (the area available to water flow) Ravina & Magier (1984) K rs b s f s K = = 1 K R v 2/ RF enlarge curvature of water flow paths and create additional hydrological resistances to water flow

9 The principle NUMERICAL DARCY EXPERIMENT v = K s h L Vertical steady state water flow through cross section of 1 x 1 m 2 Initial condition - full saturation, Pressure head gradient: 1 m, upper and lower boundary condition: +1 cm pressure head RF incorporated as impermeable objects in 1 x 1 m 2 cross section If L = 1 m and Δh = 1 m v = K s Assumptions: 1/ zero retention capacity of RF 2/ tight contact between RF and soil matrix 3/ soil matrix properties were the same for different stoniness 4/ RF were not in contact with each other

10 NUMERICAL DARCY EXPERIMENT PRESSURE HEADS Largest positive pressure heads above RF HYDRUS-2D (Šimunek et al., 2008) Smallest negative pressure heads below RF

11 NUMERICAL DARCY EXPERIMENT WATER CONTENTS HYDRUS-2D (Šimunek et al., 2008) Unsaturated zones below RF

12 NUMERICAL DARCY EXPERIMENT WATER FLUXES Non-uniform water fluxes in soil HYDRUS-2D (Šimunek et al., 2008) Minimum water fluxes, approaching zero, above and below RF

13 NUMERICAL DARCY EXPERIMENT WATER FLUXES 2D model 3D model R v = 31 % R v = 21 % in 2D: 35 objects in 3D: 403 objects!!!

14 NUMERICAL DARCY EXPERIMENT 1/ The stoniness was the most important factor (decrease by 70% at stoniness of 0.5) 2/ The second important factor was the orientation of the large ellipses (vertically, the lowest decrease 40%, and horizontally, the largest decrease 70% in K rs ) 3/ Different shapes of RF (circles, small ellipses, triangles) showed the similar influence on K rs as regular / irregular distribution of RF

15 NUMERICAL DARCY EXPERIMENT WATER FLUXES ANISOTROPY K y < K x POSSIBLE CONSEQUENCES: Ellipsoidal RF cause local anisotropy producing faster lateral outflow Preferential flow is certainly important phenomenon at hillslope scale, but RF can enhance outflow formation too

16 If you liked this presentation you can read more in: Hlaváčiková, H., Novák, V., Šimunek, J. (2016): The effects of rock fragment shapes and positions on modeled hydraulic conductivities of stony soils, Geoderma 281, Hlaváčiková, H., Novák, V. (2014): A relatively simple scaling method for describing the unsaturated hydraulic functions of stony soils. J. Plant Nutr. Soil Sci., 177, Hlaváčiková, H., Novák, Holko, L. (2015): On the role of rock fragments and initial soil water content in the potential subsurface runoff formation, Journal of Hydrology and Hydromechanics, 63,

17 Thank you for your attention!