This paper describes current practice in road surface and subsurface drainage in Sweden and analyzes the necessity for adaptation of the planning, construction, operation, maintenance and monitoring of road drainage measures to climate change. Based on a survey of professionals working with various aspects of road drainage, the study sought to identify: (1) problems experienced concerning road drainage, focusing on the current Swedish climate; (2) future problems regarding climate change impacts such as flooding and high flows; and (3) suggestions for adaptation measures concerning road drainage systems, taking future climate change into account. Suggested improvements concerning management and planning included clarification of responsibility for drainage issues, better overview of the location and condition of drainage facilities, inclusion of drainage system maintenance in procurement of operation contracts, maintenance plans for drainage facilities, and monitoring and inspection of drainage measures. Suggestions concerning drainage system construction, operation and maintenance included increasing the capacity of drainage facilities, stabilizing ditch slopes and various measures to prevent clogging of culverts.

The consequences of heavy rainfall and other extreme weather events are strongly influenced by land use within watersheds. The tested catchment consists of arable land, forest, living areas, and a creek which crosses a main road at the bottom of the catchment. The theoretical hydrological responses to different land use changes and four different extreme events were quantified by model simulations using MIKE-SHE. Land use composition and configuration was found to affect discharge; clear-cutting on 30% of the catchment area produced a 60% increase in peak discharge and a 10% increase in total runoff during a 50-year summer event. There were only small effects on peak discharge during smaller storms. Reforestation of 60% of basin area was the most effective measure to reduce peak flow, mainly for smaller (2-, 5- and 10-year) storms. Grassed waterways reduced water velocity in the stream and resulted in a 28% reduction in peak flow at the catchment outlet with the same 50-year event. A smaller degree of reforestation (30%) of the basin area was the most efficient measure to decrease total runoff. Hence different measures may be the most efficient for peak discharges and total runoff from the area. The specific effect of land use measures on catchment discharge depends on their spatial distribution and on the size and time of storm events.

Four hydrological models (LISEM, MIKE SHE, CoupModel and HBV) were compared with respect to their capability to predict peak flow in a small catchment upstream of a road in SE Norway on an hourly basis. All four models were calibrated using hourly observed streamflow. Simulated and observed discharge generated during three types of hydrological situations characteristic of winter/spring conditions causing overland flow were considered: snowmelt, partially frozen soil and heavy rain events. Using parameter sets optimised for winter/spring conditions, flows simulated by HBV coupled with CoupModel were comparable to measured discharge from the catchment in corresponding periods. However, this combination was best when all the parameters were calibrated in HBV. For ungauged basins with no real-time monitoring of discharge and when the spatial distribution is important, MIKE SHE may be more suitable than the other models, but the lack of detailed input data and the uncertainty in physical parameters should be considered. LISEM is potentially capable of calculating runoff from small catchments during winter/spring but requires better description of snowmelt, infiltration into frozen layers and tile drainage. From a practical road maintenance perspective, the usefulness and accuracy of a model depends on its ability to represent site-specific processes, data availability and calibration requirements.