Negative effects on water quality are created by eutrophication of the world’s water resources. Mitigation measures have been implemented, but poor improvements in water quality have been observed. Two-stage ditches have the possibility to increase nutrient and sediment retention to reduce eutrophication in receiving water bodies. A two-stage ditch has floodplain terraces on each side of the ordinary main channel. The terraces are available for flooding during high water flows and enables decreases in flow velocities. However, more knowledge is needed about the two-stage ditch and its effect in Swedish landscapes. The aim of the project was to study the two-stage ditch design with focus on water retention. Optimization of the two-stage ditch design was made by modeling and simulating design parameters and vegetation in the software Hydrologic Engineering Center’s River Analysis System (HEC-RAS). An existing two-stage ditch in Sweden was used as base and comparison to the theoretical model. In addition, a climate change scenario was studied to evaluate the impact of increased storm events in a two-stage ditch. Results showed that increased retention time of water, nutrients, and sediments theoretically can be given by designing two-stage ditches with maximum terrace width and minimum terrace height, and with terraces angled away from the main channel. Vegetation should also be kept on both terraces and in the main channel of the two-stage ditch to increase retention time. The study also showed that the two-stage ditch design has the possibility to decrease peak water levels during storm events, which can be expected to increase in the future. The impact on transport of nutrients and sediments from more future extreme hydrological events needs further studies. / Negativa effekter i vattenkvalitet skapas av övergödning i världens vattenresurser. Åtgärder för att begränsa övergödningen har genomförts, men svaga förbättringar i vattenkvalitet har noterats. Tvåstegsdiken har möjligheten att öka retentionen av näringsämnen och sediment för att minska övergödning. Ett tvåstegsdike har terrasser på vardera sida om den vanliga mittfåran. Terrasserna är tillgängliga för översvämning vid höga vattenflöden, vilket möjliggör minskning av flödeshastigheter. Dock krävs mer kunskap för tvåstegsdiken och dess effekt i svenska landskap. Syftet med projektet var att studera designen av tvåstegsdiken med fokus på retention av vattenflöde. Optimering av tvåstegsdikens design genomfördes via modellering och simulering av designparametrar och vegetation i programvaran Hydrologic Engineering Center’s River Analysis System (HEC-RAS). Ett befintligt tvåstegsdike i Sverige användes som bas och jämförelse mot den teoretiska modellen. Ett scenario för klimatförändring studerades även för att utvärdera effekten i ett tvåstegsdike då fler stormevent sker. Resultaten visade att ökad retentionstid for vatten, näringsämnen, och sediment teoretiskt kan ges genom att designa tvåstegsdiken med maximal terrassbredd och minimal terrasshöjd, samt med terrasser vinklade bort från mittfåran. Vegetation bör även behållas på terrasser och i mittfåran av tvåstegsdiket för att öka retentionstiden. Studien visade även att tvåstegs- dikets design har möjligheten att minska toppflöden vid stormevent, vilka kan förväntas öka i framtiden. Påverkan på transport av näringsämnen och sediment från fler framtida extrema hydrologiska event kräver ytterligare studier.

The purpose of this study is to empirically investigate the occurrence of Step 1 measures ofthe “four step principle” and the role of Strategic Choice of Measures (SCM) as it pertains tothe development of a sustainable transport system. The “four step principle” has been a partof Swedish transport planning for the last two decades with the purpose of modernising it. Byimplementing SCM the “four step principle” was supposed to take a central role in planning.SCM was supposed to offer an earlier and more open process to make strategic, nationaltransport planning more efficient and enable new perspectives in the process. However, newperspectives are few and far between and it is questionable how sustainable the measuressuggested in SCM processes actually are. The step-wise examination of the “four stepprinciple” seldom leads to suggestions where Step 1 measures are a considerable part, andit is even unclear what Step 1 actually is. Going beyond the SCM process it is questionable ifthe Measure data bank (Åtgärdsbanken), where all SCM-recommended measures aresupposed to be registered, works as a data and knowledge management database.This thesis steps in at that point.The goal of this report is to explain what Step 1 actuallyrepresents, how this is expressed in the SCM methodology and what the output of the SCMprocess is. By text analysis of documents from 150 SCM processes with possible Step 1measures an examination is made of what Step 1 represents and how Swedish TransportAdministration and other participants in SCM processes reach the measures suggested.What kind of so called primary Step 1 measures that are generated in the SCM process isalso within the scope of this report. In addition a more detailed investigation of patterns isperformed for SCM processes that generate primary Step 1 measures, pertaining to thedelimitation and actor setup in SCM:s. This is done in order to answer questions surroundingthe process of generating measures in SCM is concerned, and also to attempt to answer thecriticism that has been brought forth concerning the SCM process.The main conclusion of this report is that there are clear flaws in the SCM process. Theseshortcomings and flaws include difficulties in classifying measures, that particularly Step 1measures are packaged without individual effect evaluation, and that the process at largelacks the “rethink” perspective which the SCM process aims at. Looking at the primary Step1 measures generated, they are characterised as having a time scope connected to otherplanning processes, a limited, local geographical expanse, and as being multi-modal. Theresearch shows a contrast in that certain primary Step 1 measures occur at particulargeographical delimitations. Two common conditions for the generation of primary Step 1measures are the exclusion of Step 4 in the generation of measures, and packeting of Step1 measures for ease of handling. When investigating the SCM process the criticism that isbrought forth towards it shows signs of being legitimate. At the same time it is clear the theMeasure data bank does not function correctly as a data and knowledge management bankand improvements are needed for it to serve its intended purpose.Keywords: “four step principle”, Strategic Choice of Measures, sustainable transport,transport planning, Measure data bank, actor, Step 1, Primary Step 1 measure, instrument.