Hrund Ólöf Andradóttir

Impact of exchange flows on wetland flushing

National Institute of Environmental Health Sciences. Superfund Basic Research Program (grant P42-ES04675)

Thermal Mediation by Littoral Wetlands and Impact on Lake Intrusion Depth

Lake inflow dynamics can be affected by the thermal mediation provided by shallow littoral regions such as wetlands. In this study, wetland thermal mediation is evaluated using a linearized dead-zone model. Its impact on lake inflow dynamics is then assessed by applying the model sequentially to the river reach, wetland, and lake. Our results suggest that littoral wetlands can dramatically alter the inflow dynamics of reservoirs located in small or forested watersheds, for example, by raising the temperature of the inflow during the summer and creating surface intrusions when a plunging inflow would otherwise exist. Consequently, river-borne nutrients, contaminants, and pathogens enter directly into the epilimnion, where they enhance eutrophication and the risk of human exposure. The addition of a littoral wetland has less significant effects in larger watersheds, where the water has already equilibrated with the atmosphere upon reaching the wetland and sun shading is less prominent.

Thermal mediation in a natural littoral wetland: Measurements and modeling

National Institute of Environmental Health Sciences (Superfund Basic Research Program, grant P42-ES04675)

Assessment of flood hazard in a combined sewer system in Reykjavik city centre

Short-duration precipitation bursts can cause substantial property damage and pose operational risks for wastewater managers. The objective of this study was to assess the present and possible future flood hazard in the combined sewer system in Reykjavik city centre. The catchment is characterised by two hills separated by a plain. A large portion of the pipes in the aging network are smaller than the current minimum diameter of 250 mm. Runoff and sewer flows were modelled using the MIKE URBAN software package incorporating both historical precipitation and synthetic storms derived from annual maximum rainfall data. Results suggest that 3% of public network manholes were vulnerable to flooding during an 11-year long rainfall sequence. A Chicago Design Storm (CDS) incorporating a 10-minute rainfall burst with a 5-year return period predicted twice as many flooded manholes at similar locations. A 20% increase in CDS intensity increased the number of flooded manholes and surface flood volume by 70% and 80%, respectively. The flood volume tripled if rainfall increase were combined with urban re-development, leading to a 20% increase in the runoff coefficient. Results highlight the need for reducing network vulnerabilities, which include decreased pipe diameters and low or drastically varying pipe grades.

Status of small water supplies in the Nordic countries: Characteristics, water quality and challenges

Access to safe water is essential for public health and is one of the most important prerequisites for good living and safe food production. Many studies have shown that non-compliance with drinking water quality standards in small water supply systems is much higher than in large systems. Nevertheless, people served by small water supply systems have the right to the same level of health protection. Actions are therefore needed to improve the situation. The objective of the present study was to carry out a baseline analysis of the situation in the Nordic region and provide recommendations for governmental policy and actions. Data were gathered on number of water supplies, population served, compliance with regulations and waterborne disease outbreaks from various sources in the Nordic countries. The collected data showed that there are about 12500 regulated water supplies, 9400 of which serve fewer than 500 persons. The number of unregulated and poorly regulated supplies is unknown, but it can be roughly estimated that these serve 10% of the Nordic population on a permanent basis or 2.6 million people. However, this does not tell the whole story as many of the very small water supplies serve transient populations, summerhouse dwellers and tourist sites, with many more users. Non-compliance regarding microbes is much higher in the small supplies. The population weighted average fecal contamination incidence rate in the Nordic region is eleven times higher in the smaller supplies than in the large ones, 0.76% and 0.07%, respectively. Registered waterborne disease outbreaks were also more frequent in the small supplies than in the large ones.