REYKJAVÍK, ICELAND AUGUST 11-13, 2008 - Veðurstofa Íslands

The table 2 shows a great difference in annual precipitation in Reykjavik
and at Vifilstaðir or 336mm/yr. The temperature at Vifilstaðir is slightly
higher in summer than in Reykjavik but in autumn slightly low. The
developer, Þekkingarhúsið EHF, is keen on the winter runoff conditions in the
area, Thorolfsson, (2004).
In urban hydrology time and area scale are different from that in hydrology
in rural catchments, i.e. minutes or hours vs. days and months and m 2 and
hectares vs. km 2 . The urban runoff is characterized by a quick response
compared to rural runoff, because of impervious surfaces, lined surfaces,
vegetation removal and drainage facilities such as pipes etc for quick
conveyance of the stormwater out of the catchment.
When planning and designing urban stormwater facilities data on shortterm
rainfall are required. Jónasson et al. (1994) has analyzed the
precipitation data in the Reykjavik region regarding designing stormwater
facilities and presented so-called M5-curves. These curves can be used to
design stormwater facilities at Urriðavatn. Such IDF-curves are presented in
Aasen et al. (2005) prepare by Sigurdsson (2004) for the Urriðavatn area,
based on M5 = 53.5 mm/day.
STORMWATER MANAGEMENT AT LAKE URRIDAVATN
Goals and criteria for stormwater management are to relay on regulation
and requirements to protect Lake Urriðavatn, Umhverfismálaráðuneyti Íslands
(1999). The following goals and criteria were prepared for stormwater
management in urbanized areas:
• The stormwater is to be managed locally i.e. it is not to be conducted
out of the watershed, because the water balance in Lake Urriðavatn is
to be maintained
• The stormwater is to be treated, because the water quality in the Lake
Urriðavatn is to be affected as little as possible and may meet the
requirements to the future water quality.
• The runoff intensity in developed areas should differ as little as
possible from that before urbanization. The drainage system must be
designed in such a way that damages and inconvenience during flood
don’t occur
• The stormwater is to be utilized as a local resource for experience,
recreation and biological diversity.
The strategy to achieve these goals and criteria are as follows:
• Developing guidelines for stormwater management, which each
developer is required to follow it on his lot and property
• As much as possible of the stormwater should be conducted into the
ground or conducted to natural runoff near the source, such as roof
water, road water, water from parking places
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