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Preferential water flow in a glacial till soil
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
2005 (English)In: Nordic Hydrology, ISSN 0029-1277, Vol. 36, no 1, 1-11 p.Article in journal (Refereed) Published
Abstract [en]

Measured and simulated response of runoff during snowmelt has suggested that preferential water flow occurs as part of the infiltration process in glacial till. However, only a few quantitative studies have been presented. TDR measurements of soil water content were performed during the growing period in a till slope (7-10%) outside Stockholm. Soil cores were used to determine the water retention curve and the saturated hydraulic conductivity. A physically based one-dimensional model was used to simulate soil water dynamics in the slope. Two simulation approaches were used: a strict one-domain Darcian approach and a two-domain approach accounting for a bypass of the matrix flow system. The measured response of soil water content occurred within the first few hours after rainfall. This was best represented by the two-domain approach, while the response for the one-domain approach was significantly delayed with time and depth. The general behaviour of the soil water content throughout the season was, however, best simulated with a one-domain approach. The results indicated that preferential flow patterns through the unsaturated zone does not need to be considered to describe the seasonal pattern in glacial till soil. However, the results also point out that the purpose of the simulation is decisive when choosing a simulation approach, depending on whether the general soil water content over the season or the instant behaviour immediately after rainfall is of major interest.

Place, publisher, year, edition, pages
2005. Vol. 36, no 1, 1-11 p.
Keyword [en]
infiltration, macropore, runoff; two-domain, unsaturated
National Category
Physical Geography
Identifiers
URN: urn:nbn:se:kth:diva-5472ISI: 000228802600001Scopus ID: 2-s2.0-18144387575OAI: oai:DiVA.org:kth-5472DiVA: diva2:9847
Note
QC 20100901Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2012-02-08Bibliographically approved
In thesis
1. Urban microclimate and surface hydrometeorological processes
Open this publication in new window or tab >>Urban microclimate and surface hydrometeorological processes
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The urban near surface atmosphere is of great concern since it affects the climate to which an increasing amount of people are immediately exposed. This study investigated the microclimate in central Stockholm in terms of the thermal conditions in the 0-2.5 m air layer and the water and heat exchange processes at different types of surfaces found within the urban environment. The main objective was to improve our understanding of the urban small-scale climate system.

The urban microclimate was measured in terms of vertical air temperature profiles along a horizontal transect running through a vegetated park and its built-up surroundings during three clear and relatively calm summer days. The results showed that the air temperature at 1.2 m height within the park was 0.5 to 1.5 K lower than in the surrounding city blocks, and that the thermal stratification was generally stable (increasing temperature with height) in the park and unstable (decreasing temperature with height) in the built-up areas. In addition, there were a few examples of temperature gradients orientated in different directions within the lowest 2.5 m air layer, indicating horizontal advection between the park and the built-up areas. Climate conditions simulated with a three-dimensional microclimate model agreed well with observations and the model was therefore assumed to provide reasonable representations of important climate processes such as surface-air energy exchange processes. However, there were some discrepancies between observations and simulations that are discussed in terms of differences in real and modelled heat storage processes and wind conditions. Processes that need to be included for a more precise model description of areas such as the Stockholm environment include dynamic heat storage in buildings and dynamic wind forcing during the course of the simulation.

A soil-vegetation-atmosphere transfer model was used to study soil water transport, the surface energy balance of an asphalt surface, and the impact of urban climate on evapotranspiration. Based on model calibration to field measurements of soil water content in a till catchment outside Stockholm, new parameter values were estimated that can be used for water flow modelling of till soils. The heat fluxes of an asphalt surface were reliably simulated without knowledge of site-specific calibration and the model was useful in identifying problems with energy balance closure based on measurements only. Simulations of ‘urban’ modifications to the forcing climate conditions demonstrated that increased air temperature, and thereby increased vapour pressure deficit, had most effect on evapotranspiration from tall vegetation, while increased long-wave radiation raised grass evapotranspiration the most.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. viii, 24 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1027
Keyword
CoupModel, ENVI-met, roughness sub-layer, urban heat island
National Category
Physical Geography
Identifiers
urn:nbn:se:kth:diva-3879 (URN)91-7178-295-8 (ISBN)
Public defence
2006-03-24, Sal D3, Lindstedtsvägen 5, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100901Available from: 2006-03-14 Created: 2006-03-14 Last updated: 2010-09-01Bibliographically approved

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