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Report, 1997

Avrinningsmönster i ett litet åkerområde under 40 år av successiv urbanisering

Djodjic, Faruk


A long-term series (1952-1990) of water discharge at Ultuna was studied to evaluate impacts of changed landuse on water discharge. During this period substantial changes with increased urbanisation and new agriculturai management occurred. Urbanisation led to establishment of new conditions for water flow paths. Besides measurements, the SOIL model has been used as well as other methods to estimate water discharge. A comparison between an earlier period and a period after urbanisation showed that an increased discharge can be expected as a consequence of increased area under hard surfaces. The area with hard surfaces has been estimated to 3-5 % in period 1952-1959 and 20-25 % in latter period. Calculations with these values for hard surfaces resulted in increased discharge compared to simulations with out hard surfaces with 6-11 and 25-27 % respectively, depending on the distribution of precipitation. However, it is more the pattern of water discharge that make a difference between periods than the amount of water. The most obvious difference occurred during summer months. On one hand, precipitation over areas with hard surfaces cause almost immediate response in form of surface runoff. On the other hand, the discharge from arable land is either missing because of soil water deficit or delayed in case that the soil is near saturation. Differences in peak-flows occurrence and behaviour were traced as well. Even the low precipitation during periods with increased hard surfaces caused high peak-flows but the duration were shorter. Discharge from small watersheds is more sensitive to changes caused by an increased area of hard surface. Urbanisation is not the only way to decrease water infiltration and increase surface runoff. Modern agriculture involve the usage of heavy machinery which can decrease conductivity due to packing. However, no obvious changes were found in the present data that could be explained by changed soil properties.

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Publisher: Institutionen för markvetenskap, avdelningen för lantbrukets hydroteknik

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