title: Seymour Township and Goulburn River Environs Floodplain Controls council: mitchell state: vic category: constraint classification: MAJOR status: active last_compiled: 2026-05-31 source_docs:
- seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf
- Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf
- Mitchell Planning Scheme Map No 3LSIO-FO.pdf
Seymour Township and Goulburn River Environs Floodplain Controls
Seymour’s floodplain controls operate as a linked system: mapped statutory overlays identify land affected by flood risk, emergency-management documents explain flood behaviour and warning thresholds, and the 2006 mitigation investigation tests whether structural works could reduce township-scale flood damages. (Source: Mitchell Planning Scheme Map No 3LSIO-FO.pdf) (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.3) (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.1-1)
The main planning implication is that flood risk at Seymour is not a single river-edge constraint: the Goulburn River, Whiteheads Creek, Sunday Creek, Lake Eildon’s attenuation function, local drainage behind any levee, and statutory referral requirements all interact before land can be assessed as suitable for subdivision, dwellings, fill, or flood mitigation works. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, pp.3-7) (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, pp.6-4-6-10)
Background
Seymour is located on the Goulburn River floodplain, with Whiteheads Creek flowing along the eastern edge of the township before entering the Goulburn River. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.1-1) The flood record cited in the local flood sub-plan identifies major or notable flood years including 1916, 1917, 1934, 1952, 1973, 1974, 1975 and 1993. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.3)
The 1916 and 1917 floods are described as the largest floods in Seymour’s history, and the sub-plan states that those floods contributed to the business centre concentrating along Station Street rather than the original Emily Street location. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.4) The 1973 event is identified as Seymour’s most severe flash flood from Whiteheads Creek and involved one fatality. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.3) The 1974 event is described as the largest flood since Lake Eildon filled, with the flood sub-plan recording a Seymour gauge peak of 7.64 metres, or 137.884 metres AHD, approximately 0.64 metres above the major flood level and equivalent to about a 30-year ARI event. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.4)
The planning-control base was informed by flood inundation mapping prepared for Seymour, which the flood sub-plan states was intended both for the flood warning system and as base mapping for statutory land-use planning controls in the Mitchell Shire planning scheme. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.3) The planning scheme map extraction confirms that Mitchell Planning Scheme Map No 3LSIO-FO applies Land Subject to Inundation Overlay and Floodway Overlay mapping in the Seymour area, with the map printed on 10 January 2006 and associated with Amendment C27. (Source: Mitchell Planning Scheme Map No 3LSIO-FO.pdf)
Analysis
Flood Behaviour and Planning Mechanism
The Goulburn River catchment upstream of Seymour is approximately 8,600 square kilometres and includes Sunday Creek, Whiteheads Creek, King Parrot Creek, the Yea and Murrindindi Rivers, Home Creek, and the Acheron and Rubicon Rivers. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.3) This matters for planning because Seymour’s flood exposure is not generated only by rainfall at the township: runoff and storage behaviour across a large upstream catchment influence local flood levels. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.3)
Lake Eildon is a material dependency in the flood-risk mechanism because the flood sub-plan states that it significantly attenuates flows to the Goulburn River. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.3) During the October 1993 flood, Lake Eildon reduced peak discharge from 170,000 ML/day inflow to 46,630 ML/day peak outflow, but the sub-plan also warns that future dam-safety requirements may reduce the same level of surcharge-based flood mitigation if the reservoir is full. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.4) The practical planning consequence is that mapped flood risk should be treated as a managed-system outcome, not merely a natural-channel outcome, because upstream storage operation can affect downstream flood severity. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.4)
The flood sub-plan identifies the mapped 1% event as the area that may be inundated in a major flood representing a 1-in-100-year frequency. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.4) For assessment purposes, that means subdivision, dwellings, fill, drainage, and access decisions need to be tested against the flood extent and design levels rather than against recent flood memory alone. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, pp.4,6-7)
Statutory Overlay Controls
The planning scheme map extraction shows Floodway Overlay and Land Subject to Inundation Overlay mapping across the Seymour locality on Map No 3LSIO-FO. (Source: Mitchell Planning Scheme Map No 3LSIO-FO.pdf) The flood sub-plan links those controls to subdivision and dwelling approvals by stating that, where the Goulburn Broken Catchment Management Authority is the referral authority, planning approval may require potential house sites to be above the determined 1% flood level. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.6)
The sub-plan states that subdivision conditions may require selected fill to build up house sites, and that larger subdivisions may require drainage plans and retarding basins. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.6) This creates a direct cause-and-effect chain: if land is inside a mapped flood constraint, subdivision design may need to allocate area and engineering capacity for fill, drainage infrastructure, and flood conveyance, which can alter site layout and developable area. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.6)
The sub-plan also states that dwellings may be permitted in flood fringe areas where inundation does not exceed 500 millimetres, does not create danger to life or health, and floor levels are 300 millimetres above the 1% AEP flood contour. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.7) The same section states that industrial and commercial buildings are to be dealt with on their merits in accordance with Victorian Planning Provisions flood-management practice notes. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.7)
Flood Warning Thresholds and Urban Consequence
The flood sub-plan gives indicative Goulburn River gauge thresholds for Seymour of 4.0 metres for minor flooding, 5.2 metres for moderate flooding, and 7.0 metres for major flooding. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.12) It describes minor flooding as affecting low-lying areas next to watercourses, moderate flooding as potentially requiring evacuation of some houses and covering main traffic routes, and major flooding as inundating extensive rural areas and appreciable urban areas with possible isolation and numerous evacuations. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.12)
These thresholds matter for planning because land-use decisions need to preserve not only finished-floor immunity but also access, evacuation feasibility, road network function, and floodway capacity. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, pp.6-7,12) The sub-plan states that planning approvals may be conditioned on providing and maintaining floodways, and warns that floodways should not later be restricted or obstructed by fences, buildings, or other works. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.7)
Quantified Damages and Mitigation Rationale
The 2006 WBM report estimated Seymour’s annual average flood damages at 490,000 using flood inundation maps from the Seymour Flood Study and ANUFLOOD damage assessment guidelines. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-1) For a 1-in-100-year event, the report estimated 288 flood-affected properties, 263 buildings flooded above floor level, and total estimated damages of 14.6 million. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-1) For a 1-in-50-year event, it estimated 282 affected properties, 235 buildings flooded above floor level, and 8.7 million in damages. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-1) For a 1-in-20-year event, it estimated 277 affected properties, 147 buildings flooded above floor level, and 3.4 million in damages. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-1)
The damage profile explains why the mitigation investigation moved beyond mapping into structural options: even lower-frequency floods were expected to produce substantial above-floor flooding in the existing township. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-1) The report assessed four detailed options: an inner town levee on the 1984 SRWSC alignment, an outer town levee on the 1984 SRWSC alignment, an outer town levee on an alternative alignment, and lowering Emily Street with associated waterway crossing works. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-2)
The preferred option was the alternative outer town levee, later amended to include an extension from Villers Street to the Eastern Railway Line along Whiteheads Creek. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-4) The preferred design standard was a 100-year ARI levee with 600 millimetres freeboard. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-10)
Levee Impacts, Costs, and Residual Risk
The preferred levee was modelled using the TUFLOW model established for the Seymour Flood Mapping Study. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-4) The modelling found that construction of the preferred levee would increase flood levels upstream of the town by approximately 0.6 to 0.8 metres, with small isolated areas immediately adjacent to the levee near Eliza Street experiencing increases of more than one metre. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-5) The modelling also found that changes in peak flow speed were generally between 0 and 0.2 metres per second. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-5)
The levee would not remove all flood consequences because seven properties outside the preferred alignment were already flooded in the 100-year event under existing conditions and would experience increased flood levels and increased flood frequency as a result of the levee. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-5) The report states that individual property solutions should be considered for those properties at detailed design stage. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-5)
The cost estimate for a 100-year levee with 0.6 metres freeboard and pumps was 3.91 million, compared with 3.32 million for a 50-year levee with freeboard and pumps and $2.71 million for a 20-year levee with freeboard and pumps. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-10) The 100-year option had the highest benefit-cost ratio at 1.54, compared with 1.12 for the 50-year option and 0.02 for the 20-year option. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-10)
The cost estimates excluded some residual design items because the report states that levee costs did not include local drainage modifications other than pumps, and it separately notes that emergency spillways and relief channels may be required at additional cost. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, pp.6-9-6-10) This is a key implementation risk because the preferred concept depends on internal drainage, flap gates, pump sizing, and potential breach-management infrastructure being resolved before a final scheme could be relied on for land-use or emergency-management purposes. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, pp.6-6-6-10)
Community Preferences and Decision Tension
The WBM questionnaire received 34 returns. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-2) Respondents ranked damage to houses or businesses as the leading flood concern at 24% of total responses, followed by warning time at 18%, personal financial hardship at 17%, economic effects on the community at 15%, personal safety at 14%, and damage to other property at 13%. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-2)
The preferred mitigation measures in the questionnaire were community education and awareness programs at 17%, flood proofing or raising individual buildings at 17%, land acquisition at 16%, land-use planning at 14%, floodways at 10%, levees or floodwalls at 9%, vegetative cleaning of waterways at 9%, and enlargement of existing waterways at 8%. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-2) This shows a tension between community preference and technical recommendation: levees ranked sixth in stated community preferences, but the engineering and economic assessment selected an outer town levee as the preferred structural option. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, pp.5-2,6-2-6-10)
The same questionnaire found that 50% of respondents preferred protection against a 20-year flood, 40% preferred protection against a 50-year flood, and 10% preferred protection against a 100-year flood. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.5-3) The technical assessment nevertheless selected the 100-year ARI design standard because it produced the highest benefit-cost ratio. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-10)
Current Status
The source set confirms that Seymour has mapped FO and LSIO controls on Mitchell Planning Scheme Map No 3LSIO-FO, printed 10 January 2006 and marked with Amendment C27. (Source: Mitchell Planning Scheme Map No 3LSIO-FO.pdf) The source set does not include the current ordinance clauses, current schedules, current VicPlan layer extract, or any later amendment history confirming whether the 2006 preferred levee was funded, designed, constructed, abandoned, or superseded. (Source: Mitchell Planning Scheme Map No 3LSIO-FO.pdf) (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.7-2)
The 2006 report recommended that Council adopt the report findings, consult affected landowners, resolve concept design issues for pumping and levee location, review scheme costs, and prepare a Floodplain Management Plan for public comment under section 223 of the Local Government Act. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.7-2) The available source set does not include that subsequent Floodplain Management Plan or any adoption record. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.7-2)
Dependencies
- Blocks: Unresolved flood levels, floodway capacity, finished-floor requirements, and drainage design can constrain subdivision layout, dwelling siting, fill placement, and building permits on affected land. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, pp.6-7)
- Blocked by: Any levee implementation is blocked by detailed design of levee alignment, pumping requirements, local drainage capacity, emergency spillways, landowner consultation, cost review, and a Floodplain Management Plan process. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, pp.6-6-6-10,7-2)
- Informed by: The controls and mitigation work are informed by the Seymour Floodplain Mapping Study, the flood sub-plan, the Mitchell Planning Scheme FO/LSIO map, and the WBM mitigation investigation. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.3) (Source: Mitchell Planning Scheme Map No 3LSIO-FO.pdf) (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, pp.1-1,2-1)
- Implements: The mapped controls implement floodplain risk management through planning permit referral, floor-level expectations, drainage conditions, and protection of floodways. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, pp.6-7)
- Conflicts with: The preferred levee creates residual adverse impacts for seven properties outside the alignment and increases upstream flood levels, so mitigation for the township can transfer or intensify risk in specific locations unless detailed design resolves those effects. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.6-5)
Cross-Jurisdictional Links
The Goulburn Broken Catchment Management Authority is identified as the regional floodplain-management body and as the referral authority for relevant planning approvals. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.6) Goulburn-Murray Water is relevant to flood-risk interpretation because Lake Eildon’s attenuation function and dam-safety operating assumptions affect downstream Goulburn River flood behaviour at Seymour. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.4)
The Bureau of Meteorology was represented on the Technical Steering Committee for the WBM mitigation investigation, and the flood sub-plan separately links warning categories and gauge heights to flood response actions. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.2-1) (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, p.12) These links mean Seymour floodplain controls sit across local planning, regional catchment management, state water-storage operations, and emergency warning systems. (Source: seymour_township_and_goulburn_river_environs_flood_sub-plan.pdf, pp.4,6,12) (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.2-1)
Gaps in This Analysis
The most important corpus gap is the Seymour Floodplain Mapping Study Final Report, March 2001, which the WBM mitigation report identifies as the source of the TUFLOW model, design flood extents, depths, velocities, and mapping used for both flood-risk communication and mitigation assessment. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, pp.1-1,3-1) Without that report, this page cannot independently test parcel-level flood depths, velocity hazards, flow paths, afflux locations, or the exact translation from flood modelling to FO/LSIO boundaries. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.3-1)
A second gap is the absence of current Mitchell Planning Scheme ordinance text for the Floodway Overlay, Land Subject to Inundation Overlay, schedules, referral requirements, and any incorporated floodplain-management documents. (Source: Mitchell Planning Scheme Map No 3LSIO-FO.pdf) Without the current ordinance, this analysis can identify the mapped presence of FO and LSIO controls but cannot state the current permit triggers, exemptions, decision guidelines, or schedule variations for affected Seymour land. (Source: Mitchell Planning Scheme Map No 3LSIO-FO.pdf)
A third gap is the absence of later Council records showing whether the 2006 preferred levee proceeded to a Floodplain Management Plan, detailed design, funding, construction, or abandonment. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.7-2) This limits the current-status assessment because the available source set establishes a recommended mitigation pathway but not its implementation outcome. (Source: Seymour Flood Mitigation Communication Investigation Final Consultants Report to Council February 2006.pdf, p.7-2)