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Hydrological response of sedum-moss roof

In English

Författare

Summary, in English

Eco-roofs are becoming popular for aesthetic reasons and also as units of stormwater systems. It is thought that such roofs with soil cover and vegetation reduces the total runoff, the peak flows and improves the quality of the roof water. Here are reported investigations of runoff from thin, 3-4 cm soil, extensive green roofs with sedum-moss in southern Sweden. The two-year study was performed on new roofs in the eco-city Augustenborg and also on nearby old vegetative roofs. The rain intensity and the roof runoff were measured with 5 min, or in some experiments with 1 min, resolution. The annual runoff from the eco-roofs was about half that from hard roofs and was close to that of small natural rivers. However, although most rainy days there was no or little runoff from the roofs, the highest observed daily runoff values were close to the daily rainfall. Runoff is initiated, when the soil is at field capacity. Thereafter the hourly runoff corresponds closely to the hourly rainfall. For short-term high intensity storms, the runoff peak is attenuated relative the rain intensity. The time of concentration for runoff was experimentally determined applying artificial rains on existing roofs and on experimental roof plots with varying slopes and using different drainage layers. The peak runoff from the roofs was found to correspond to the rain intensity over 20-30 minutes. The probability of high rain intensity is much higher than the probability of high runoff. When intensity-duration-frequency curves were constructed, runoff with 0.4 year return period corresponded to rain with 1.5 year return period. The influence of the slope of the roofs on the runoff peak was minor as was the effect of drainage layer. The vertical flow in the soil dominates the runoff process. The influence of extensive sedum-moss vegetated roofs on runoff quality was also studied to ascertain whether vegetated roofs behave as sink or source of pollutants and whether the runoff quality changes with roof age. The results show that in general vegetated roofs behave as a source of contaminants. With the exception of a 15-year old roof, the studied vegetated roofs contributed phosphate-phosphorus to the runoff. Some metals appeared in concentrations that corresponds to moderately polluted water. However, nitrate-nitrogen is retained by the vegetation and the soil.

Publiceringsår

2004

Språk

Engelska

Dokumenttyp

Konferensbidrag: abstract

Ämne

  • Water Engineering

Conference name

AGU (American Geophysical Union) Fall Meeting, 2004

Conference date

2004-12-13 - 2004-12-17

Conference place

San Fransisco, United States

Status

Published