2019 SUDS Proposal Hadsten City IONELA TAMASAN BUSINESS ACADEMY AARHUS | VIBY J Contents Introduction ................................................................................................................................ 2 Current situation. Challenges ..................................................................................................... 2 Proposal...................................................................................................................................... 5 Retention pond ....................................................................................................................... 7 Pond dimensions .................................................................................................................... 8 Pond design .......................................................................................................................... 10 Replacement of hard surface in the car parking lot and the path ways with permeable surface .................................................................................................................................. 11 Conclusion ............................................................................................................................... 12 Appendix 1 Blue map .............................................................................................................. 13 Appendix 2 Blue map of the area represented together with the water channels along with the water’s flow direction .............................................................................................................. 14 Bibliography............................................................................................................................. 15 Introduction Denmark, as many other countries is expected to experience consequences caused by the global climate change phenomena (Arnbjerg-Nielsen, 2006). The most likely consequences identified are extreme rain storms events of different intensities that are expected to cause damage not only to agricultural crops but to infrastructure and buildings alike. For example, the sewer system in Denmark is designed to collect both waste water and rain water. In the past, this worked very well, however, in case of extreme rainfall the capacity of the system exceeds, and the extra water will cause flooding. Denmark is considering replacing the old sewer system with a new system which will separately collect the two types of water i.e. rain water and waste water. This way flooding episodes caused by low capacitated sewer system can be overcome (Gregersen, 2015). The Danish government has requested each municipality in Denmark to prepare a climate change adaptation plan based on its specific characteristics and needs, meaning precipitation expected to fall in the next years, temperature changes, elevation of the area, nature types (Danish Energy Agency, 2008). Favrskov Municipality has identified based on a calculation model 8 areas in the municipality that are in the most risk of flooding. The model includes a mapping of all the area prone to flooding risk as well as the level of damage expected, this way the most vulnerable areas are prioritized. The two consultancy firms, Orbicon and COWI were responsible for carrying the calculation. The methods used were the cloudburst maps SCALGO adjusted to the hydraulic model and considered annual average precipitation 700mm/year. The map was then adjusted in consideration to the hydraulic conductivity (data used from the Danish Nature Agency). Aside this hydraulic MIKE FLOOD mapping was carried. This model offered a better understanding on the connection between the terrain and the sewers system and the probable flooding caused by it. (Christiansen, 2013) One of the risk areas identified is Hadsten ( Favrskov Kommune, 2013). The city has as an approximate population of 8.086 with an area of 5,29 km² (ErhvervsNyhederne, 2016). The city centre is crossed by LilleÅ, a stream with a total length of 31400 m. The flood map indicates that the risk of flooding is high and is expected to affect buildings, roads, paths, living areas as well as parking areas and technical facilities within the following 5 streets: Evald Tangs Alle, Stationsstræde, Søndergade, Ved Åen, Ågade. The city centre is often affected by heavy rainfall especially during winter as the water level in Lilleå rises so much that the meadows from the east and west side of the stream cannot store and drain the excess water. ( Favrskov Kommune, 2013) Current situation. Challenges The following proposal will focus on a specific area, i.e. the parking lot and the recreational area located on Ågade street (56°19'34.6"N 10°02'42.6"E). Along this site the stream Lille å is running. Due to the heavy rain that is increasing over the years, combined with the hard surfaces on the parking lots as well as some parts of the recreational area, that prevent the excess water from draining in to the ground, and the fact that on some part of the stream the height of the banks is very low, causes the very fast flooding episodes. Figure 1Lille å during a cloudburst. Retrieved from (Favrskov Kommune, 2013) Figure 2 Lille å screening cloudburst. Retrieved from ( Favrskov Kommune, 2013) Based on the maps (Fig.2,3,4) prepared by Niras for Favrskov Municipality the area lying close to and around Lilleåen is subjected to high flooding probability events. The events are expected to significantly increase from year 2013 to year 2110 as a result of water level increase in the stream as well as the water increase over all due to the low-lying area the city of Hadsten is located in ( Favrskov Kommune, 2013). Figure 3 The flood map in the event of cloudburst. Retrieved from (Favrskov Kommune, n.d.) Figure 4 Flood screening at Hadsten, along Lilleåen. The card section shows one 10 (red), 20 (green) and 100-year events (blue) in 2012. The specific location the proposal is focusing on is located in a catchment area, meaning that the water from the soundings runs towards that particular direction, influencing the flooding possibility. Figure 5 Blue map of the area represented together with the water channels along with the water’s flow direction (Ionela Tamasan,2019 As shown in the map from Fig. 5 the area in discussion is likely to experience flooding since is located in a low-lying area and much of the water flowing from the hills reaches this particular zone. The intensity of the colour on the blue map represents the depth value and as seen from the map the colour is relatively constant, however the value near the stream is rather worrying (between 1.5-2.5). During January 2011, the Ernst B. Sund Plads and Ågade areas were significantly affected by the excess water (fig.6) that ran from Lilleåen, and more than a few houses as well as Kvickly super market were flooded to some degree. ( Favrskov Kommune, 2013) As the area is located in the middle of the city, where private proprieties/houses exist, a cost value of 8 is allocated. (On the scale from 1 to 10 where 10 represents the highest cost value and 1 the lowest) (Favrskov Kommune, n.d.) The parking lots next to the stream, have all hard surface that do not allow the water to drain. This is one of reasons for the flooding in the area. Figure 6 Flooded area, on the left. Retrieved from (LILMOES, 2011). Usual appearance of the area without flood, on the right (Ionela Tamasan 2019) Proposal The SuDS (Sustainable Drainage Solution) proposed includes two different solutions combined (see fig.7), that will contribute to the flooding prevention, will enhance wild life, will contribute to an aesthetically appealing recreational area, but most crucial will constitute a feasible solution for the flooding episodes. First solution proposes the establishment of a retention pond in an already established recreational area close to Lille å, that is expected to collect most of the excess water in case of flooding caused by the stream. The second solution proposes the replacement of the hard surfaces in the two parking lots next to Lille å, on Ågade street, with permeable surface that will allow a better drainage of the excess water in case of flooding. The pathways in the recreational area are hard surface as well thus, those are proposed to be replaced as well with permeable surface. The two solutions are connected, and they are meant to support each other. Considering the fact that the pond will be placed in a recreational area where small children play around, the depth of it cannot be high in order to avoid possible accidents. This means that less water will be stored in the pond and will have to be handled in another way, in this case by the permeable pavements. Figure 7 SuDS proposed: retention pond and hard surface replacement on the parking lots and path ways on the recreational area The replacement of the hard surface with permeable surface will notably contribute to the water management in the area. The solution chosen is locking concrete pavers (fig.8). The excess water will be collected into underground reservoirs. Further the water can be used for non-potable usages without the need of being treated. In the drainage process the water is filtered and will end up in the reservoir relatively clean. (California Department of Transportation Division of Design Office of Storm Water Management, 2014) Figure 8 Permeable Pavement with locking concrete pavers. Retrieved from (David J. Sample, 2013) Retention pond The area designed for recreational use has permeable