BEFORE THE HEARING COMMISSIONER In the Matter of: The Resource Management Act 1991 And Proposed Rangitikei District Plan Change 2016 Application by: Rangitikei District Council Section 42A of the Resource Management Act 1991 Report by Alistair Beveridge Flood Hazard Mapping Dated: 15 June 2016 1 1.0 Introduction 1.1 My name is Alistair Beveridge. I am a Director of The Catalyst Group, an environmental management consultancy firm based in Palmerston North. 1.2 I hold the following qualifications: • Bachelor of Science (Honours), majoring in Physical Geography from the University of Otago 1992, and • Master of Science, in Fluvial Geomorphology (the study of waterway form and function), from the University of Otago 1995 1.3 Work experience relevant to this matter includes: • Two years (1996-1997) with Manawatu-Whanganui Regional Council (now known as Horizons Regional Council) as an Environmental Management Officer. My sole duty during this time was compiling available flood hazard information to prepare regional flood hazard maps. The flood hazard maps I developed were adopted into the first generation District Plans for the seven district and city councils making up the Manawatu-Whanganui region. • Three years (1997-1999) with Manawatu-Whanganui Regional Council as an Environmental Management Officer where I was responsible for: (1) the continued compilation of existing and new flood hazard information, and (2) provision of flood hazard information to members of the public and in response to resource/building consent enquiries from district/city councils, surveyors and developers. I was the first person to occupy the position that Horizons Regional Council now calls the District Liaison Officer. • During the remainder of my time with Horizons Regional Council (1999-2011) I undertook a number of flood-related duties that were additional to my normal day-to- day functions. These included: o preparing the regional Flood Hazard manual, a series of documents produced by Horizons Regional Council detailing the nature and extent of natural hazards in the region, which informed regional civil defence response and was a base document for the Lifelines (risks to essential infrastructure) assessment, o a variety of roles during flood events, including a major logistical role in the response to the 2004 flood event o was a trained Moutoa Spillway gate operator, and o co-authored a summary document on the major 2004 flood event, and was the lead liaison with Te Manawa Museum during the development of an exhibition on the same flood event and its aftermath. • Five years (2011-present) as a Director of The Catalyst Group, providing expert advice to Rangitikei District Council on a variety of matters, including flood hazards, as part of the District Plan review process (2010-13), and current plan change process. 1.4 I have read the Code of Conduct for Expert Witnesses in the Environment Court’s Consolidated Practice Note 2014 and agree to comply with it. The evidence presented in this statement is within my area of expertise. I have not omitted to consider material facts known to me that might alter or detract from the opinions I express. 2 2.0 Scope of Statement 2.1 This report is provides background on the methodology employed to prepare the flood hazard maps appearing in the Operative District Plan, and the methodology used, and justification for, revising the flood hazard map for Tutaenui Stream and Hunterville, which is the subject of a plan change. 3.0 Original Flood Hazard maps 3.1 I was originally employed by Manawatu-Whanganui Regional Council in 1996 to: (1) compile the available existing flood hazard information, (2) prepare regional flood hazard maps, and (3) provide the flood hazard maps to the seven district/city councils in the region for inclusion within their first generation District Plans. These maps were adopted into all seven District Plans, and even into several second generation District Plans. 3.2 This was the first attempt by the regional council to consolidate the available flood hazard information into a single, readily available form, for passing onto district councils, who are the principle controllers of land use. Up until this point, available knowledge on the flood hazards was patchy, spread across different departments within council, only in people’s heads, and various external sources. 3.3 My first task was to collect the various flood hazard sources and pieces of information together. This involved a detailed search of council and external organisation records, interviewing long-serving staff members and ex-staff members (particularly field officers and those in the river engineer department), compiling and cataloguing an extensive flood photograph library. 3.4 The second step involved the transfer of this information onto regional maps so the location and extent of flooding could be visibly displayed. However, the available information was incomplete and not all of the same quality or reliability. As such, a hierarchy was applied to the information in regards to reliability and how much weight could be applied to it for mapping purposes. The hierarchy was as follows (from most reliable to least): • modelled flood extents by council or other reputable firms • photographs of flooding (slightly less reliable, because they are invariably taken after the peak of flooding) • written descriptions, and • oral recollections 3.5 The best and most complete information was for urban centres, river management scheme areas, and areas that had recently experienced major flooding. Unfortunately, this left large areas of the region with little or no information, even though many areas were still expected to experience flooding. 3.6 As such, a third step requiring a different approach was required to fill in the gaps in these areas. This approach invovled the assessment of topographic maps, aerial photographs, and the interpretation of vegetation and river forms (e.g. terraces, and human structures) to estimate where flooding was likely to occur in a large flood event. A limited number of field visits were used to refine the estimates generated by the desk-top assessment. This approach drew upon my fluvial geomorphology background. 3 3.7 The final step involved drawing (with pencil) the collated flood hazard information onto 1:50,000 topographic maps, and larger scaled (more detailed) maps where the reliability of the available information supported this. This drawn information was then digitised into council’s GIS system. The GIS flood hazard layer was in turn made available to the city/district councils. 3.8 The methodology and information used was not infallible, and errors could be introduced in a number of ways: • inaccuracies or errors in the original data • mis-interpretation of flood photographs • incorrect interpretation of maps, aerial photographs and vegetation/river forms, and • drafting and digitising errors 3.9 Reflecting the differences in quality and reality of the available information, the use of methods to estimate flooding extent, and likely errors this created in flood hazard maps, instructions were provided to city/district councils on how the maps should be interpreted and used. The maps identified Flood Hazard 1 and Flood Hazard 2 areas. Flood Hazard 1 being those areas with the most accurate information, and the most extensive flooding in terms of depth and velocities. Such areas were to be avoided for future development, as were activities likely to cause damming or diverting of floodwaters onto neighbouring and downstream properties. 3.10 In contrast Flood Hazard 2 was based on less accurate information, and councils, professionals and members of the public were encouraged to make contact with the regional council regarding any proposals so a site assessment could be made. 3.11 It was always the intention the flood hazard maps would be updated in response to new information (e.g. records from more recent flooding, new modelling) or changing requirements (e.g. One Plan’s 0.5% AEP (200-year return period) flood threshold). 4.0 Proposed Flood Hazard Map Amendments 4.1 As part of the proposed Rangitikei District Plan change process I was engaged by the Council to provide expert advice on flood hazard mapping matters, as they related to Tutaenui Stream and Hunterville. In providing this advice I adopted methodologies that were consistent with: (1) those outlined above, and (2) the intention to base decisions on the most accurate and reliable information available. 4.2 I detail the advice and input provided for the Tutaenui Stream and Hunterville separately below. 5.0 Tutaenui Stream 5.1 Horizons Regional Council recently completed a revision of its flood model for the Tutaenui Stream (the primary source of flooding in Marton and Bulls). As such, this is the most up-to- date and most accurate flood information available for this waterway, and should be adopted into the District Plan in preference to the existing flood information. 4 5.2 However, given the model was limited in its extent (i.e. it did not extend upstream of the various flood detention dams situated on tributaries of the Tutaenui Stream), existing flood information beyond the model boundaries should be retained. 6.0 Hunterville 6.1 The original flood hazard map for Hunterville was generated on the basis of: • Recollections of staff • Interpretations of topographic maps, aerial photographs, and vegetation/river forms 6.2 No site visit was made to confirm the original flood hazard map for the township which is at risk from flooding from both the Porewa Stream and a small unnamed tributary that flows through the town from the West, parallel with Bruce Street. 6.3 As part of the plan change process I visited Hunterville with the intention of confirming and where necessary reviewing the flood hazard map for the township. My visit confirmed there were a number of errors associated with the original flood hazard map.