New techniques for urban river rehabilitation

Transcription

1 New techniques for urban river rehabilitation (WP8) URBEM Urban River Basin Enhancement Methods New techniques for urban river rehabilitation Methodology Work Package 8 LNEC João Rocha Elsa Alves EVK-CT June 2005 Deliverable 8.1 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology i

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3 New techniques for urban river rehabilitation (WP8) URBEM Research Contractor Contact Details Laboratório Nacional de Engenharia Civil Av. Brasil, Lisboa, Portugal Tel/fax / web site All methodologies, ideas and proposals in this document are the copyright of the URBEM project participants. These methodologies, ideas and proposals may not be used to change or improve the specification of any project to which this project relates, to modify an existing project or to initiate a new project, without first obtaining written approval from those of the URBEM participants who own the particular methodologies, ideas and proposals involved. This report is a contribution to research generally and it would be impudent for third parties to rely on it in specific application without first checking its suitability. The URBEM partner organisations accept no liability for loss or damage suffered by the client or third parties as a result of errors or inaccuracies in such third party data. Dissemination Status Public Report Authors João Soromenho Rocha, Laboratório Nacional de Engenharia Civil (LNEC), Lisbon, Portugal jrocha@lnec.pt Elsa Alves, Laboratório Nacional de Engenharia Civil (LNEC), Lisbon, Portugal ealves@lnec.pt Deliverable 8-1 New techniques for urban river rehabilitation. Methodology i

4 URBEM New techniques for urban river rehabilitation (WP8) Summary In this deliverable it is presented the methodology for the application of techniques on rehabilitation of urban rivers, taking into account the information available from other Work Packages and the research on river engineering. Contributions to this document represent findings on experience gained in the analysis of case studies and on the experience of the river engineering practice on the countries of the URBEM partners. The rehabilitation of urban rivers includes the knowledge of adequate techniques, and its relations with all needed type of interventions, both before and after the implementation of techniques. The technical interventions are divided in two main groups: interventions to be practised in the drainage basin (controlling the hydrological processes) and interventions to protect maintain and improve the hydromorphological conditions in stream channels (controlling the hydraulic processes in bed and banks). The other associated deliverable 8.2 consists on a set of documents, namely, recommendations, specifications and guidelines. In the description of methodology there are remissions do that deliverable and also other deliverables of URBEM project, guiding the application of techniques to other aspects of the urban river rehabilitation. ii Deliverable 8-1 New techniques for urban river rehabilitation. Methodology

5 New techniques for urban river rehabilitation (WP8) URBEM Contents 1. Introduction Initiative for urban river rehabilitation Initiative in case studies Methodology for the initiative in urban river rehabilitation Site definition in urban river rehabilitation Site definition in case studies Methodology for site definition in urban river rehabilitation Two ways for site definition Site definition for urban river rehabilitation Site definition for urban rehabilitation including its associate river Formulation of river rehabilitation Introduction Assess baseline condition in urban river rehabilitation Set objectives Set boundaries Identify controlling factors Development of options Introduction Identify options Describe the consequences of options Score and choose options Monitoring of rehabilitated urban river Introduction Decide what to monitor Design monitoring programme Implement option and monitoring Review monitoring results References ANNEX Deliverable 8-1 New techniques for urban river rehabilitation. Methodology iii

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7 New techniques for urban river rehabilitation (WP8) URBEM 1. Introduction One of the specific technical and scientific objectives of the URBEM research project is "to develop innovative urban watercourse rehabilitation techniques for use in future schemes". This objective is covered by Work Package 8 - New techniques for urban river rehabilitation (WP8). The deliverable 8.1 presents the methodology to adopt sound techniques for urban river rehabilitation. The techniques for urban river rehabilitation may be applied to the drainage basin (controlling the hydrological processes) and to protect, maintain and improve the hydromorphological conditions in stream channels (controlling the hydraulic processes in bed and banks). There are different types of techniques in both groups. However, the application of techniques shall be done in a harmonized procedure where beside the technique implementation; other aspects of river rehabilitation are taken into consideration. Consequently, the proposed methodology considers the tool developed to assess the potential for urban watercourse rehabilitation (Work Package 5), the implementation and review of the assessment tool (Work Package 6), the decision support methodologies (Work Package 9) and finally the development of indicators of success (Work Package 10). A great importance was done to the result of the work done for the Work Package 2, existing case studies, providing a base for the choice of the techniques and for the understanding of relative success of different techniques. The reflexions on the behaviour of different techniques and the conceptual research developed in the project had done the opportunity to define the proposed methodology. In a minor way it is also incorporate the work developed in the study-site monitoring (Work Package 3) and aesthetic evaluation (Work Package 4). The deliverable 8.2 complement the present deliverable. The deliverable 8.2 is a set of recommendations, specifications and guidelines. The recommendations on how to naturalise flow regimes is the first work document prepared in WP8. Information from Work Package 2 - Existing Case Studies, was used to define current methods for re-naturalising watercourse flow. The recommendations are divided into 5 chapters, namely, Characterisation of flow regimes, Modifications of flow regimes in urban areas, Water Framework Directive and flow regimes, Procedures for re-naturalising flow regimes and Recommendations on how to re-naturalise flow regimes. The procedures for re-naturalising flow regimes in urban rivers are divided in two main groups: measures to be practised in the drainage basin (controlling the hydrological processes) and measures to protect, maintain and improve the hydromorphological conditions in stream channels (controlling the hydraulic processes in bed and banks). The two groups are divided in six types of measures. Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 1

8 URBEM New techniques for urban river rehabilitation (WP8) All types of measures may be applied in each case, depending on the modifications the urbanisation has imposed. Only measures for river basin are to be used when the river channel did not suffer significant modifications. Rarer is the case where there are no modifications in the river basin; this may happen when an urban area is situated near a large river, where only the interventions on river channel are done, and the urban area is a small percentage of the entire river basin area. In this case only measures on river channel and banks are needed. The general situation is to apply both types of measures. The recommendations to re-naturalise the flow regimes in urban rivers include the assessment of the present situation and of the previous situation of the flow regime, before the intervention on river basin/channel; the comparison of both situations in order to obtain the synthesis of the modifications imposed by the presence of urban areas in the river basin; the choice of the measures to be designed for the river basin or/and river channels and banks; the Implementation of measures and the definition of a monitoring plan if considered necessary for the follow-up of the re-naturalisation. The recommendation on incorporation of wetlands, floodplains and sustainable drainage methods into urban schemes is the second work document prepared in WP8. The recommendations are divided into 5 chapters, namely, Wetlands in rivers, Characterisation of floodplains in rivers, Influence of urban drainage systems on rivers, Procedures to define urban schemes near rivers and Recommendations on incorporation of wetlands, floodplains and sustainable drainage methods into urban schemes. Presently, wetlands in urban areas may serve for flood control, for water quality issues and for recreation and wildlife purposes. Within the river rehabilitation concept, retention facilities close to residential and commercial areas are used as parks, playgrounds and artificial wetlands. One important percentage of wetlands is generally associated with floodplains. Many cities have grown on floodplains and urban planning has to account for potential inundations, as flooding is part of the natural hydrological cycle. Design of flood control measures often base on a 100-year event, but it is more and more understood that however large the design capacity is, catastrophic events may overwhelm this magnitude or technical measure may fail. Flood damage reduction rather than flood protection is a more realistic goal for urban areas. Considering the remaining risk even when sound structural measures are present there is always necessary to develop emergency measures and catastrophe management. The design of sustainable urban drainage facilities is not primarily a technical problem but more of an institutional concern, basically the cooperation between different departments in a city s administration. City administration tends to follow well established principles of clear responsibility boundaries. The nature of urban drainage normally requires joint ownership and operation. This often necessitates interdepartmental cooperation in city councils in areas were often no well established 2 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology

9 New techniques for urban river rehabilitation (WP8) URBEM lines of communication and assignment of responsibilities exist. The choice of SUD measures is highly dependent on political and public support. Other crucial factors in most installations are land availability, types of pollutants to be removed, groundwater levels, soil types, construction costs, maintenance costs and desired pollutant removal. The specifications of new materials and techniques are mainly dedicated to the interventions on the rivers itself, namely to improve instream morphology (by classical river engineering and by soil bio-engineering), to interventions in drainage basin or to protect the flood in the river valleys. The design of sustainable urban drainage facilities, and the interventions in drainage basin, is not primarily a technical problem but more of an institutional concern, basically the cooperation between different departments in a city s administration. However, it is included in the specifications. The specifications are prepared for three main domains related to the rivers: the instream interventions, the river valley interventions and drainage basin interventions. The first are also divided in two types of interventions: the classical river engineering and the soil-bioengineering. Considering that division of interventions they are prepared two specifications documents, each one for one of the types previously defined. The Specifications 8.1 deals with the river engineering, using classical methods of intervention, although taking into account the specific case of urban river rehabilitation. The Specifications 8.2 deals with soil-bioengineering instream interventions. Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 3

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11 New techniques for urban river rehabilitation (WP8) URBEM 2. Initiative for urban river rehabilitation 2.1 Initiative in case studies In the Work Package 2, Existing case studies, it was presented how the urban river rehabilitation case studies were started. The most used initiatives are from public administrative institutions, almost 90 % of the cases. The fact the river are, in general, administered by public institutions shall be the major reason to find that. In second place the initiative is coming from civic stakeholders. It is thought a significant percentage of civic stakeholders are in certain way in relation with public institutions. The two major type of initiators of urban river rehabilitations have in general a technical staff, where the perception of the techniques to be used are known. The other two explicit types of initiators are the interest groups and the need to respond to legal demands. In those two types it is less probable to find technical staff to take into consideration the technical aspects by itself. It also important to know the reasons to initiate urban river rehabilitation. The same Work Package shows the major objective to the urban river rehabilitations is the ecological improvement, almost 100% of cases. However, the term ecological shall be considered in an extended way, as it is explained later. The second two objectives are the amenity/recreation and urban recreation. Both are urban driven objectives, being the first one a river driven objective. At a relative low distance appears flood control as an objective. In this case there is a joint river and urban driven objective. The last objectives to initiate urban river rehabilitations are the public involvement, visual improvement and education. Al three are social driven. The term ecological is, in certain way, related to the terminology of the EU Water Framework Directive (WFD). Indeed, all subdivisions considered in the analysis of objectives for the ecological improvement use concepts defined in the in the WFD. The most named objective is the stream morphology, 50 % of cases. The second objective is the water quality. The following objectives are related with the first one: hydrology/hydraulics, continuum and lateral connectivity. The last two objectives are the target species and the vegetation. Both are directly related with last of the three components defined in the WFD, the ecology. It is remarkable that the objectives are in very evident ranking, first in the hydromorphology component, next the water quality and finally, the ecology. Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 5

12 URBEM New techniques for urban river rehabilitation (WP8) 2.2 Methodology for the initiative in urban river rehabilitation It is clear there are two main reasons to initiate a new urban river rehabilitation process: to rehabilitate a river that it is in a bad condition, referred to the transformations its channel, its water or its habitats had suffer during the urbanisation process, or to rehabilitate the urban area around the river, referred to the historical evolution of the urban occupation. These two types of reasons are completely different, departing from different rationales, although there are some common parts in the rehabilitation processes. In the proposed methodology there is a strong emphasis in the first type of reasons, the rehabilitation of the river itself. Of course, the rehabilitation of the river demands an intervention on urban aspects, but they may appear as a need, and as a consequence, and not as a point of start. It is the rehabilitation of the river that forces the use of the appropriate techniques to deal with river channel, river banks and river basin, in general. On contrary, when the reason is to do an intervention in the urban area, contemplating the river passing in that area, the river rehabilitation is a consequence, and in that condition, the rehabilitation in the river is only to obtain a better urban area. Of course, the hydromorphological, water quality and ecological aspects shall be taken into consideration, but they tend to be considered secondary objectives, unless they are included members in the team that deal in an adequate way the technical considerations for the river features. It is proposed the initiative to rehabilitate urban rivers, independently of the main reason to do that, shall include the scope inserted in the EU Water Framework Directive (WFD). The instream interventions to improve the morphology of river in urban rivers, the water quality and the ecological conditions of rivers within Europe shall comply with the WFD. In this it is expected, but for that purposes it is also needed, to have the appropriate hydromorphology of the river, river bed and river banks. This is applicable either in natural rivers or in Heavily Modified Rivers. The last case is present in almost cases in the urban rivers subjected to rehabilitation. When the initiative for river rehabilitation is done by the River Basin Administration is natural the process considers all aspects defined in WFD. When the initiative for river rehabilitation is done by Urban Administrations shall be made contacts with the River Basin Administration in order to guarantee the process also includes the WFD scope. According to WFD one of the main objectives of the instream interventions is to achieve good ecological conditions by combining water resources management and city planning, hence improving the quality of life. The interventions shall be done with 6 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology

13 New techniques for urban river rehabilitation (WP8) URBEM the best practicable technology and the present methodology is made to guide cities how to achieve good ecological potential in its urban rivers. The rehabilitation of urban rivers shall result of a planning process that may start a few years leading to the implementation of measures involving stakeholders that define goals and objectives and setting quantifiable targets that can be monitored. Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 7

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15 New techniques for urban river rehabilitation (WP8) URBEM 3. Site definition in urban river rehabilitation 3.1 Site definition in case studies Site definition within case studies has displayed as well subjective approaches as methodological approaches. In the majority of case studies, about 70 %, the sites were defined with existing knowledge, no selection method being applied. In remaining case studies the site definition is based in a selection method. But these definitions have been determined by three different specific and complementary reasons: city wide, river network based or basin wide assessments. Again, the site definition, as the initiative, is commanded or by city administration or by river administration (network or basin). The methods used to assess (potential) rehabilitation were the following (Table 7 in deliverable of Work Package 2): Area wide assessments of water body state (including in landscape planning, water body development plans, territorial development programmes, landscape assessments); Impact analysis and assessments; Ecological studies analysing restoration potential; Pilot projects/on-site tests; Site visits and assessment of the knowledge of stakeholders. The aspects covered were the following: Significance of reducing water pollution; Potential for ecologic rehabilitation, e.g. re-colonisation; Significance of social/aesthetic/cultural/economic enhancement Potential to reduce flood damage Site ownership and boundary lines. It is noteworthy the aspects covered did not included explicitly the largest type of intervention, in the river morphology, although it may appears in the reduction of flood damage aspect. The space and time scales are also important characteristics to be taken into consideration in the site definition. In the case studies they were analysed the width and length of the rehabilitated sections. The largest ranges of width were 1-5 m (stream) and 5-25 m (small river), both with 30% of cases; the third range was less than 1 m width (streamlet) in 23% of cases; the range m (large river) had 9% of cases, and finally in 4% of cases the range was m (major river). In 4% of cases no information was available. Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 9

16 URBEM New techniques for urban river rehabilitation (WP8) The lengths of rehabilitated sections of water courses showed also a wide range: the largest ranges of length were m and 1-2 km m, both with 22% of cases; the third and fourth ranges were 2-3 km and larger than 3 km, in 17% of cases; the range km had 9% of cases, and finally in 9% of cases the range was less 100 m. The mean length was about 2000 m. According to the authors of the Work Package 2 deliverable, the emphasis of the survey to primarily consider complex rehabilitation approaches with good practice character, larger scheme may prevail. In fact, it can be assumed that a much higher proportion of spatially restricted schemes may be found in European cities. According to the deliverable of Work Package 2, rehabilitation projects range in scale from incorporating an entire drainage basin down to single interventions along very short reaches of water courses. Urban river rehabilitation projects very often are combined with a general upgrading of the more or less close surrounding of the water course itself. Not seldom the schemes comprise the landscaping of the adjacent land, the establishment of new paths or facilities for information. For this reason the land areas affected by rehabilitation projects also differ in size but without close relation to the size of water course addressed. The average duration from initiation to implementation of a scheme took between 6 to 8 years, varying from a few months up to about two decades. Implementation duration averaged 2.9 years, varying from a few weeks to 15 years. Longer time periods usually were connected to basin wide or citywide programmes, while shorter time periods related to less complex, site related projects. 3.2 Methodology for site definition in urban river rehabilitation Two ways for site definition The site definition is made by two different main processes, in relation with main scope of the intervention, and by consequence, the technical aspects of river rehabilitation. One of the main processes is centred in the river itself, although some urban aspects are necessarily included. In this process the driving forces are in the River Basin Administration or equivalent institutions. The main scope is to rehabilitate the river, situated in an urban area, taking into consideration the target a better river, and by consequence also a better urban in the adjacent area, banks and flood valleys. In this case, it is natural to find an emphasis on the river techniques. A joint work to city administration is needed. The other main process is centred in the urban rehabilitation near an existing bad river. Of course, the river aspects are also necessarily included, but in a certain way more as an urban solver. In this process the driving forces are in the Urban 10 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology

17 New techniques for urban river rehabilitation (WP8) URBEM Administration or equivalent institutions. The main scope is to rehabilitate the city, situated near a river, taking into consideration the target a better city, and by consequence also a better river passing there, with its banks and flood valleys saw as urban zones. In this case, it is natural to find an emphasis on the urban techniques. A joint work to River Basin administration is needed. The site definition for these two main processes is not the same, although some aspects are necessarily present in both Site definition for urban river rehabilitation When the rehabilitation of an urban river is initiated is needed to define the river reach. There are not rigid rules to define the site where the rehabilitation is to be implemented. However, using the WFD terminology is possible to define simple criteria to define the site where the rehabilitation is to be done. Considering the type and intensity of efforts to be used in the rehabilitation it is possible to divide the type of intervention, and consequently the site definition. The first basic distinction is the 1) Instream river rehabilitation; 2) River basin rehabilitation (including or not the instream). The instream river rehabilitation is concentrated in the main channel, and its lateral adjacent zones where the flood pass. The site definition contemplates, at least, the definition of the downstream and upstream cross sections. This is relatively straightforward but only an expert in flow regimes can find the appropriate cross sections to tackle with the hydraulic aspects. The definition of the adjacent areas, equivalent to the flood prone area, is relatively more difficult, being advisable to use a step by step approach, unless previous data gives directly the right definition. An accurate definition is cost and time consuming. At a first guess a rough definition may be done with the analysis of geomorphology and geology maps, or with the help of the inhabitants knowing the history of past river floods, or analysing probable flood marks. The other more accurate definitions for the flood prone area will be done based in hydraulic modelling of present, past or future situations. The hydraulic modelling needs good river data to guarantee reliable results. The calibration and validation of hydraulic modelling shall be imposed because is the only way to be successful in the proposed river rehabilitation. For hydraulic modelling is needed to define the contributing river basin. That definition is only to determine the river discharge to be used in the computation. In Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 11

18 URBEM New techniques for urban river rehabilitation (WP8) some cases the river basin is entirely outside the urban area, in other cases the contrary may be found, all area is in the urban area. These two limiting cases are quite different in the implications the study may have. The last case may generate a chain of scenarios for the reciprocal influence of river basin and instream. The river basin definition is relatively simple on the conceptual point of view, it is to determine the river basin boundaries, where the river processes are generated and transported to the river channel. Indeed, the river basin, a spatial area where complex physical, chemical and biologic processes are generated and transmitted downstream, may also be viewed as a network of small streams going from the river basin boundaries downstream to the lower cross section where the river basin is defined. The next distinction in the site definition is related with the type of intervention in the instream rehabilitation. Following also the WFD terminology, and from a soft to a hard intervention they may be defined three levels of urban river rehabilitation: a) Biological; b) Water quality; c) Hydromorphological. In a strictly sense they shall be viewed as a forced set of three aspects of an unique intervention, but in practical terms, the two first types of interventions may be used without any physical (hydromorphological) intervention. In more complex river rehabilitations it is necessary to have heavy hydromorphological interventions as a base for better water quality and biological interventions. Also, some times there is only one type of intervention. So the consideration of the three proposed levels of instream river rehabilitation to define the site is quite useful. For each level the definition of the site have some particular features. Considering again the WFD terminology, and also the rationale considered in that Directive, the base level of intervention is the hydromorphological, an element supporting the biological elements. The definition of the site shall include the three basic hydromorphological elements: the hydrological regime (quantity and dynamics of water flow and connection to groundwater bodies), the river continuity and the morphological conditions (river depth and width variation, structure and substrate of the river bed and structure of the riparian zone). Consequently for the site definition it will be necessary to gather all pertinent data related with the above to mentioned elements. From the beginning, first in a very simple way, the site definition shall consider those hydromorphological elements. For the definition of the boundaries of the site (upstream and downstream river cross sections) all those elements are needed. As each element has different types of control and influence they will be found different cross sections. Some times the hydraulic control will be dominant, imposing larger distances for those cross sections, other times the river bed structure are dominant, and so on. Consequently it 12 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology

19 New techniques for urban river rehabilitation (WP8) URBEM is not easy to find general and simple criteria to help find the border cross sections for the site. This is the reason to propose the site definition by a hydraulic expert. The same type of considerations is valid for the chemical and physico-chemical elements supporting the biological elements and for the biological elements. The chemical and physico-chemical elements include a list of parameters (general and specific pollutants) and consequently, in order to consider different types of influence and its evolution along the river, it may imply different cross section localisations for the borders of the site, either in the river itself, either in the main affluents to the river. The biological elements include the compositions and abundance of aquatic flora, benthic invertebrate fauna and fish fauna. The last element shall also consider the age structure. For each of biological element we may find different border to analyse the situation. Considering all these elements it is straightforward to conclude the site definition in the river must be done by a small team including at least to basic domains: hydraulic and biology. It is very probable that each element implies different cross section in upstream and downstream border. It is possible to assert the site definition may imply a variable geometry. This is not contrary to the fact in simple case it is enough to define only two cross sections for the border of a river reach to be subject to rehabilitation. Each of the main cross sections used as boarders of river reach to be rehabilitated defines a river basin. Some of the river basins are not urban and are not included in the rehabilitation intervention. However, others of the river basins are in the urban areas. In this case a careful definition of river basin limits shall be done, including the main sub basins inside Site definition for urban rehabilitation including its associate river When the rehabilitation of an urban area is initiated including an existing river is also needed to define the river reach. But in this case the site definition is more intensely marked by the urban scope. The definition of the river reach where the rehabilitation may occur may be influenced more by the urban site definition than by the river limit definition. Beside that, all considerations presented in are applicable. In general, in urban rehabilitation a strong presence of river basin rehabilitation (including or not the instream) is present. The instream river rehabilitation, concentrated in the main channel, and its lateral adjacent zones where the flood pass, are confined strictly with urban area, unless an appropriate hydraulic approach leads to a more technical based definition. Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 13

20 URBEM New techniques for urban river rehabilitation (WP8) The adjacent areas, defined as urban areas, may be quite different the flood prone areas. Some times they are larger, other times smaller ones. The river basin definition in an urban area may be complex, being the sub basins difficult to find, and the relations between surface processes and under ground networks, generating and transporting to the river channel water and diversified pollutants, not entirely identified for all areas. In most cases the river basin is entirely inside the urban area. The development of the urban areas creates pressures in river. The WFD also imposes the collection and maintenance of information on the type of the significant anthropogenic pressures to which the surface water bodies in each river basin district are liable to be subject (Annex II, 1.4). Among other items they are the following: 1) Estimation and identification of significant point source pollution, in particular by substances listed in Annex VIII, from urban and other installations and activities; 2) Estimation and identification of significant diffuse source pollution, in particular by substances listed in Annex VIII, from urban and other installations and activities; 3) Estimation and identification of significant water abstraction for urban and other uses, including seasonal variations and total annual demand, and loss of water in distribution systems; 4) Estimation and identification of the impact of significant water flow regulation, including water transfer and diversion, on overall flow characteristics and water balances; 5) Identification of significant morphological alterations to water bodies; 6) Estimation and identification of other significant anthropogenic impacts on the status of surface waters; 7) Estimations of land use patterns, including identification of the main urban areas and, where relevant, fisheries and forests. All type of above written items is needed to use in site definition. Indeed, when an urban area is rehabilitated, where a river is also or not rehabilitated, those items are needed to identify the pressure on the river reach. This river reach may not always be inside, or in front of, the urban area, because some actions related with water control may be sent, or received, from adjacent or larger distances from the urban area. The transfers to or from urban areas shall be taken into account in the definition site of rehabilitation area, river basin or river channel. 14 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology

21 New techniques for urban river rehabilitation (WP8) URBEM 4. Formulation of river rehabilitation 4.1 Introduction In the Work Package 5 it is described the tool for assessing potential for rehabilitation. Knowing any river rehabilitation may generate a large number of options it was chosen the multi-attribute decision making to select from a range of options. Like any other problem solution in river rehabilitation the decision maker has to: a) Set the objectives, b) Specify the criteria on which the analysis is to be based, c) Specify how the criteria on which the analysis is to be based, d) Specify the analysis method to be adopted, e) Review the results of the analysis In addition the decision maker may also be involved in: f) Developing different options to be assessed, g) Assessing the different options to be assessed. The decision maker may be a single person or may be a group; it may involve some or all of the stakeholders or their representatives. Also the problem may only one, with a large complexity, or it may be, in order to facilitate the decision, disaggregated in parts, when some independency may occur. The techniques for urban river rehabilitation, the main subject in the Work Package 8, may be one part of the disaggregation. Being or not disaggregated the complex of actions, in the methodology presented they are focused the options for the techniques used in river rehabilitation. Some remarks are made when strong links are present for other subjects related with river rehabilitation, such as urban, aesthetic, economic or social ones. As pointed out in Work Package 5, the first process in the assessment of the potential for rehabilitation is the process 1a, formulation of urban river rehabilitation. This process is divided in four parts: 1) Assess baseline condition; 2) Set objectives; 3) Set boundaries; 4) Identify controlling factors. The following sections of the methodology present these four parts of the first process applied to the techniques for urban river rehabilitation. Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 15

22 URBEM New techniques for urban river rehabilitation (WP8) 4.2 Assess baseline condition in urban river rehabilitation The assessment of the present condition of an urban river or, saw from a different point of view, an urban area where a river is running, may be done with different sensibilities, different perspectives, different interests, different institutions, shortly, is a large spectrum question. As posed by Work Package 5, this part may be done in two actions: 1. Review information on catchment and river, 2. Identify stakeholders. In the Recommendations 8.1 they are characterised the flow regimes in urban areas, in the present situation and in the previous conditions, in order to assess the river condition and the potential to be rehabilitated. Considering all elements included in that Recommendations 8.1 the following three steps are recommended to formulate the urban river rehabilitation, or to consider the re-naturalisation of the flow regimes in urban rivers: 1) To assess the present situation of the flow regime. The assessment will include the river basin and the river channel and banks elements, taking into account the information described in chapters 2 and 3, and 6.2 of the Recommendations 8.1. This assessment shall take into account the elements included in the WFD, as referred to in Chapter 3 of the Methodology. 2) To assess the previous situation of the flow regime, taking into account the information described in chapters 2 and 3, and 6.3 of Recommendations 8.1. The assessment may be done by two alternative ways; i) the real previous river regime is obtained gathering data base and historical facts and documents or ii) an ideal previous situation is obtained by comparison of neighbour unchanged river basins or by theoretical reasoning. 3) To compare both situations in order to obtain the synthesis of the modifications imposed, during all history, by the presence of urban areas in the river basin. The list of modifications is the basis to define the interventions to be applied for the river rehabilitation. From the knowledge of hydrological regime, the discharges for different time and space situations, it is possible to characterise the flow conditions in the river channels. The characterisation of channel flow processes should include the characterisation of bed and banks and the hydraulic structures. The only way to collect the required data is to survey the site. For important structures the design documents should be referred to, where hydraulic computations may be included. 16 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology

23 New techniques for urban river rehabilitation (WP8) URBEM The hydraulic computations using the available data may be relatively heavy, involving skilled human resources, appropriated models, and for good results, calibrations. It is very easy to make large errors when calibration is not done. The results of hydraulic computations are very sensitive to some input data, such as bed slope, and mainly to the roughness coefficients. There is no good method for using the right values for coefficients, unless a calibration is done or an experienced team is involved. For the alluvial rivers the difficulties are increased. The characterisation of river bed sediments should be always included. The characterisation of river flow processes should be done for the appropriate situations, being included in most cases, at least: 1) the flood events, where the river channels are small to convey all water, 2) the full bank where the beginning of flood occurs, 3) an average discharge situation, representing the more frequent situation and 4) low flow situations. For certain rivers the discharge decreases to zero, remaining, however, in most cases, sub superficial flows, and small stagnant water bodies. The computations, supported by calibrations, should deliver for the chosen cross sections, the water flow characteristics for the cases referred to above; water levels, velocities, singular flow behaviour (for instance changes of flow type, sub critical or super critical), 2D or 3D features (lateral currents, vortex). The hydraulic characterisation may advance the sediment transport and water quality characterisation, and also the biological characterisation. The degree of comprehensiveness of the hydraulic characterisation depends of the importance of the study. As the hydraulic computations are in general heavy they should be included, certainly, in large studies, but may be simplified accordingly the size of the problem. If we are dealing with a potential intervention on short reaches of small rivers it should be enough to do simple computations with a minimum of calibration procedures and light site surveys. The modifications encountered in the river channels situated in urban areas may vary from insignificant to large deviations. Similarly to the hydrological modification analysis the knowledge of the time evolution of the urban occupation is the basis for the characterisation of the previous conditions, and a reference situation shall be found. It may correspond to a situation where no urban occupation was present, or alternatively a light occupation existed. The choice is pure arbitrarily. It is evident the technical work shall be done taken into consideration the experience of all, being relevant the stakeholders, where studies may exist and personal knowledge has a precious value. 4.3 Set objectives The knowledge of the baseline condition of an urban river, or an urban area where an urban river runs, is the main base to set objectives for a potential river rehabilitation, Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 17

24 URBEM New techniques for urban river rehabilitation (WP8) or urban rehabilitation, including its river. Following the same questions for the assessment, the setting of objectives will be dependent of different sensibilities, different perspectives, different interests, different institutions, having a large spectrum scope. As posed by Work Package 5, this part may be done in three actions: 1. Set broad objectives, 2. Consultation with stakeholders, 3. Set specific objectives. In the Recommendations 8.1 they are presented, in chapter 5, the procedures for renaturalising flow regimes in urban rivers and urban river rehabilitation. They are divided in two main groups, measures to be practised in the drainage basin (controlling the hydrological processes) and to protect, maintain and improve the hydromorphological conditions in stream channels (controlling the hydraulic processes in bed and banks). The two groups are divided in six types of measures. Both types of measures may be applied in each case, depending on the modifications the urbanisation has imposed. Only measures for river basin are to be used when the river channel did not suffer significant modifications. Rarer is the case where there are no modifications in the river basin; this may happen when an urban area is situated near a large river, where only the interventions on river channel are done, and the river basin with urban areas is a small percentage of the entire river basin area. In these cases only measures on river channel and banks are needed. The general situation is to apply both types of measures. These recommendations are complemented by the Recommendations 8.2 where wetlands, floodplains and urban drainage methods are incorporated into urban schemes. It is known the urbanisation has been narrowing the watercourses to the minimum space possible. Due to urbanisation pressure and narrowing of watercourses within a very limited space, safety fencing and supporting walls have been built, as well as other buildings that strongly reduce the hydromorphological state and influence the physical state and biological state of the river. Consequently, a broad objective in river rehabilitation shall include measures to create basic conditions for widening of the stream and management of river banks. The basic problems are issues in terms of ownership rights and water-related rights linked with the buildings. Besides providing additional space for the improvement of the hydromorphological state, by widening the channel and the banks the channel flow is enhanced and the water level locally reduced. The extended channel enables meandering, formation of pools and rapids, dunes and wetland riparian areas. Also, the channel provides for a better flow of flood waters. The influence is favourable for the ecological state of the water body in its entirety. 18 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology

25 New techniques for urban river rehabilitation (WP8) URBEM The extensions can be done in several variants, i.e. widening of the river bed only, or widening of banks with different approaches and modern consolidations made of natural materials. The rehabilitation may also include the reconstruction of bridges and enhancement of their scale. The improvement of instream morphology using river engineering shall be based in well sound application of river hydraulic knowledge. It is a specialised scientific domain, and when this is neglected the success of the intervention is low. If the above referred to broad technical objectives are worked by the expert in river hydraulics, a following round of stakeholders consultation is needed to refine the setting of objectives, taking into consideration not only the technical expertise, but also the diffuse knowledge of the river problems, coming from other disciplines, and the constraints imposed by the existence of urban areas. The main broad objective for the WFD is to achieve the good ecological potential of urban streams. Consequently, the setting of specific objectives in river rehabilitation shall also follow a more natural approach, in relation with simpler hard technical approach. In the past, many rivers were stabilised and hardened with concrete and steel in order to accommodate navigation and to protect urban uses from flooding and erosion. River shorelines were typically designed for a single purpose. Today should be followed a growing support for ecology and multiple uses as well as an interest in using soft engineering of shorelines at appropriate locations. Such an approach incorporates flood conveyance concerns, aquatic habitat, riparian habitat, water quality, recreation and aesthetics. The setting of specific objectives shall take into account all these aspects. 4.4 Set boundaries Following the knowledge of the baseline condition of an urban river, or an urban area where an urban river runs, and the setting of specific objectives for a potential river rehabilitation, or urban rehabilitation, including its river it is needed to set boundaries. As posed by Work Package 5, this part may be done in four actions: 1. Define spatial extent of assessment, 2. Define time-scale for assessment of plan or project, 3. Determine resources for assessment, 4. Define success indicators and acceptability criteria (initial review to be refined during assessment. The chapter 3 of the Methodology presents the first steps to set boundaries, i.e. the site definition. In the Recommendations 8.1 they are presented, in chapter 2 and 3, respectively about characterisation of flow regimes and modification of flow regimes in urban areas, the main definitions of physical processes in rivers to help the definition of spatial and time-scale boundaries. Also the content of two chapters in Deliverable 8-1 New techniques for urban river rehabilitation. Methodology 19

26 URBEM New techniques for urban river rehabilitation (WP8) Recommendations 8.2 helps to define those boundaries. The chapter 3, about characterisation of flood plains in rivers, is related to the definition of lateral boundaries. The chapter 4, about influence of urban drainage systems on rivers, has information on the urban systems that, in a certain way, are boundaries for the river system. The definition of spatial extension of the assessment shall take into account the relative spatial scale of the river and urban areas. In Work Package 4, Deliverable 4.2, Methodology of classification of the aesthetic value of the selected urban rivers it is recognized that river width is a geometric parameter that has a strong influence on the interrelationships between the river and the city. It influences the scale of the river corridor and the waterfront and its uses, the accessibility network, the transponibility, traffic and many other factors in the urban/watercourse environment. Indeed, the scale and size of an urban watercourse within the urban morphology is a very important relationship. The river width has been chosen in the methodology of classification of the aesthetic values as one of the starting items for selecting the case study, due to its relevance in the urban context. The width of a river is a good measure of the importance of a river, and is strongly correlated with many aspects of river system and river basin upstream feeding water, sediments, and other water constituents. In Recommendations 8.1, section it is presented an available quantification of the river characteristics based in the order of the rivers. It was find out that order of the major part of the rivers to be rehabilitated are between fourth (IV) and ninth (IX) orders. That means with river basin areas and river lengths between about 2 km 2 to 300 km 2 and 2 km to 50 km. According to Recommendations 8.1 the modifications in the river net are very dependent on the space scale of the two areas, the river basin area and the urban area. Different cases can occur, and for each case different spatial extent of assessment is necessary. Case 1 Urban area much smaller than the river basin The consequences for river modification, during past times, are minor except on the part of catchment area where the urban area is settled. In this case, only a part of the river may be changed during the past. Definition of spatial extent is relatively simple, being necessary to separate the parts of rivers basin, respectively included in the urban area and outside. Case 2 Urban area covering the major part of the river basin The consequences the river may be more or less important depending where the urban area is located in the catchment. If the urban area is in the upstream part of catchment, it may significantly alter the river network in the whole catchment, not only in the urban area, but also in the downstream part. If the urban area is in the downstream part of the river network the consequences to downstream are not felt, and the urban area receives a natural river network in 20 Deliverable 8-1 New techniques for urban river rehabilitation. Methodology