Ras og jordtap som følge av flom

As soil formation is an extremely slow process, soil can be considered a non-renewable resource. Soil functions have been under critical treat globally as a consequence of many processes. An European consortium has performed the RECARE project. The main aim of RECARE was to develop effective prevention, remediation and restoration measures using an innovative trans-disciplinary approach. NIBIO Environmental division is leading WP2 of the project. The main focus in Norway is if flood risk increase, both in frequency and intensity, will lead to more streambank erosion, and if that can mask the effects of measures taken at agricultural areas to reduce particle and phosphorous losses. The experimental area in the RasFlom project is at the Hobøl river, and has as major goal to set up a Norwegian network to disseminate knowledge generated in the RECARE project, and connects to other relevant Norwegian projects and research and public partners. The most promising measures to reduce flood peaks and protect streambanks have been discussed during the previous reporting period. This year we have calculated the effectiveness of the measures. In addition, we have conducted experiments to (i) measure the effectiveness and (ii) quantify the different parameters. Finally, we have gathered stakeholders in a demonstration day to show and discuss different measures to reduce flood peaks. Streambank In an area along the Hobøl river, we have established an experiment with three different vegetation types. Model runs are done for those different vegetation types, different water levels in the river, and differences in soil water content. This is done using the BSTEM model. The scenarios that have been included in the calculations are (i) no vegetation; (ii) flooding; (iii) low water level; and (iv) high soil-water content combined with low water level in the stream (after-flood period). Vegetation types used were grass, bushes and tree. Preliminary results show that vegetation type can have an effect on stabilizing streambanks. Flood peak We have calculated the effect of retention areas, in cooperation with Haldenvassdraget water board, in the Melleby-stream area. For this, a spatial model for calculating surface runoff, flooding and erosion is used (LISEM model). We have calculated the area with and without retention ponds, and with different rainfall episodes (2, 5, 10 and 25 re-occurrence). Initial results show that use of retention ponds can be an effective measure to reduce the flood peak, which can contribute to reducing flood-risk in down-stream areas. We have started a process with the water boards of Øyeren, Haldenvassdraget, Glomma-sør and Morsa to identify potential areas for implementation of retention ponds. This has resulted in a preliminary map with possible locations, based on a decision system discussed with the water boards. Demonstration A demonstration day is organized, with stakeholders representing the agricultural agency, water boards, farmers and researchers. The day was organized in one of our experimental areas with a retention pond in Svinndal to discuss possible measures and their effectivity. Based on the observations of the farmer, flood frequency has reduced from 2-3 times each year to 1 time every second year. In an evaluation of implementation of retention ponds in the RECARE project among stakeholders, it showed that there was consensus on the advantages of implementing ?small? retention ponds in forest areas. There was, though, not a unanimous opinion if those ponds will reduce floods, since the effectivity depends on scale and amount of ponds in catchment. Concerning is also shown on the possible costs to implement a pond, as well as the security in maintaining the area. Less concern was there on the fact that some of the forest area will be used for a pond.

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Jord kan anses å være en ikke-fornybar ressurs fordi jordsmonndannelse er en ytterst langsom prosess. Globalt er imidlertid jordfunksjonene allerede kritisk truet av en rekke prosesser.Nylig har en Europeisk konsortium definert RECARE prosjektet. Hovedfor målet med RECARE prosjektet er å utvikle og validere forebygging, utbedring og gjenoppretting tiltak med en innovativ trans-disiplinære tilnærming. Bioforsk Jord og Miljø er WP2 leder i RECARE prosjektet. Et viktig spørsmål er om en økning av flomfrekvens og intensitet vil føre til akselerert erosjon av elvebredder, og om dette kan «maskere» tiltak mot avrenning av partikler og fosfor fra landbruksområder. RasFlom tar utgangspunkt i Hobølelva som forsøksområde og ha som hovedmålsetning å etablere et Norsk nettverk som kobler sammen kunnskap som resulteres fra RECARE prosjektet med Norske prosjekter og forsknings- og forvaltningsinstitusjoner. RasFloms aktiviteter er: Akt 1. Klimaendring med Norsk fokus; Akt 2. Tiltaksanalyse; Akt 3. Nettverkbygning. Ras Flom skal formidle resultater fra RECARE til flere interessegrupper, som lokale og nasjonale myndigheter, gjennom et årlig seminar. RasFlom leverer en rapport som inneholder: 1. Beskrivelse av effekter av endrende klima på vannføringen i Hobølelva 2.Overs ikt av lovende tiltak mot jordras i Hobølelva 3.Framdriftsplan om en nettverksorganisering fra forskings- og forvaltningsmiljøer om jordras problematikken langs elv områder i Norge.