Spatio-temporal relevance and controls of preferential flow at the landscape scale
<p>The spatial and temporal controls of preferential flow (PF) during infiltration are still not fully understood. As soil moisture sensor networks allow us to capture infiltration responses in high temporal and spatial resolution, our study is based on a large-scale sensor network with 135 so...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-11-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/23/4869/2019/hess-23-4869-2019.pdf |
| Summary: | <p>The spatial and temporal controls of preferential flow (PF) during
infiltration are still not fully understood. As soil moisture sensor
networks allow us to capture infiltration responses in high temporal and
spatial resolution, our study is based on a large-scale sensor network with
135 soil moisture profiles distributed across a complex catchment. The
experimental design covers three major geological regions (slate, marl,
sandstone) and two land covers (forest, grassland) in Luxembourg. We
analyzed the responses of up to 353 rainfall events for each of the 135 soil
moisture profiles. Non-sequential responses (NSRs) within the soil moisture
depth profiles were taken as one indication of bypass flow. For sequential
responses maximum porewater velocities (<span class="inline-formula"><i>v</i><sub>max</sub></span>) were determined from the
observations and compared with velocity estimates of capillary flow. A
measured <span class="inline-formula"><i>v</i><sub>max</sub></span> higher than the capillary prediction was taken as a
further indication of PF. While PF was identified as a common process
during infiltration, it was also temporally and spatially highly variable. We
found a strong dependence of PF on the initial soil water content and the
maximum rainfall intensity. Whereas a high rainfall intensity increased PF
(NSR, <span class="inline-formula"><i>v</i><sub>max</sub></span>) as expected, most geologies and land covers showed the highest PF
under dry initial conditions. Hence, we identified a strong seasonality of
both NSR and <span class="inline-formula"><i>v</i><sub>max</sub></span> dependent on land cover, revealing a lower
occurrence of PF during spring and increased occurrence during summer and
early autumn, probably due to water repellency. We observed the highest
fraction of NSR in forests on clay-rich soils (slate,
marl). <span class="inline-formula"><i>v</i><sub>max</sub></span> ranged from 6 to 80 640 cm d<span class="inline-formula"><sup>−1</sup></span> with a median of 120 cm d<span class="inline-formula"><sup>−1</sup></span> across all events and soil
moisture profiles. The soils in the marl geology had the highest flow
velocities, independent of land cover, especially between 30 and 50 cm depth,
where the clay content increased. This demonstrates the danger of treating
especially clay soils in the vadose zone as a low-conductive substrate, as
the development of soil structure can dominate over the matrix property of
the texture alone. This confirms that clay content and land cover strongly
influence infiltration and reinforce PF, but seasonal dynamics and flow
initiation also have an important impact on PF.</p> |
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| ISSN: | 1027-5606 1607-7938 |