Grange Planning Brain

title: Kilmore Flood Study council: mitchell state: vic category: constraint classification: MAJOR status: in-progress last_compiled: 2026-05-31 source_docs:

  • Mitchell Shire Council Meeting Agenda 20 November 2023.pdf
  • Mitchell Shire Council Meeting Minutes 20 November 2023.pdf
  • Kilmore Flood Mapping and Intelligence Study_Final Report.pdf
  • Kilmore Creek Flood Study Engaging Mitchell Page.pdf
  • Goulburn Broken CMA Annual Report 2019-20.pdf
  • Goulburn Broken CMA Annual Report 2021-22.pdf
  • Mitchell Shire flood study summary.pdf
  • Kilmore Flood Mapping and Intelligence Study_Final Report Executive Summary Sections 1-5.pdf

Kilmore Flood Study

The Kilmore Flood Mapping and Intelligence Study converts a previously unmapped flood constraint into a proposed statutory planning-control layer for Kilmore, with the largest planning consequence being the potential introduction of Floodway Overlay and Land Subject to Inundation Overlay controls across more than 1,700 properties in the township (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.145). The mechanism is not only a mapped hazard line: the study links hydrology, hydraulic modelling, emergency planning, building controls, potential drainage works, and a future planning scheme amendment into one constraint pathway for Kilmore (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.5-6; Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.140-145).

Background

The study was announced for funding by the Minister for Water in July 2014 and was commissioned by Mitchell Shire Council in partnership with DELWP and the Goulburn Broken Catchment Management Authority (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.1). Kilmore had no previous flood study, no stream-gauge record for Kilmore Creek, limited recent major-flood evidence, and no flood planning controls in the Mitchell Planning Scheme before the study pathway commenced (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.1, 4; Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.140).

The study area covers the upper Kilmore Creek, Ryans Creek and Hamilton Creek catchments, with catchment areas of approximately 31.4 square kilometres, 12.4 square kilometres and 9.2 square kilometres respectively (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.1). The township then had approximately 7,000 people and occupied about one third of the study area, while the remaining two thirds comprised low-density residential, rural living and grazing land (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.1).

The study was connected to the Kilmore Structure Plan because future investigation areas for residential rezoning in Clause 21.11-3 of the Mitchell Planning Scheme were used to define the developed-condition modelling scenario (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.1). Community consultation was held through two information sessions on 23 February 2017 at Kilmore Library to test draft 1% AEP flood mapping against local knowledge before finalisation (Source: Kilmore Creek Flood Study Engaging Mitchell Page.pdf). The final study was reported as complete on 16 April 2018 and was described by Council as information for emergency services, future planning and building decisions, and longer-term flood mitigation options (Source: Kilmore Creek Flood Study Engaging Mitchell Page.pdf).

Analysis

Constraint Mechanism: From Unknown Flood Risk to Statutory Controls

The central planning issue is that Kilmore moved from a position of limited formal flood knowledge to a mapped flood constraint that Council now intends to translate into the Mitchell Planning Scheme (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.140-145). Council’s 20 November 2023 agenda states that no flood planning controls currently existed for Kilmore because the township’s flood risk had not previously been surveyed and recent flood evidence was limited (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.140).

The proposed statutory mechanism is a planning scheme amendment applying the Floodway Overlay and Land Subject to Inundation Overlay, with the Floodway Overlay identified as the more stringent and prescriptive control and the Land Subject to Inundation Overlay generally directed to ensuring building levels sit above anticipated flood levels (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.145). The consultant report recommends assigning areas with depth greater than 300 millimetres and/or velocity-depth product greater than 0.4 square metres per second to the more restrictive Floodway Overlay or Urban Flood Zone, with lower hazard areas subject to the Land Subject to Inundation Overlay (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.72).

The immediate practical effect is a permit-screening and design-level constraint across a large number of lots rather than a prohibition across the whole mapped area (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.72; Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.145). Council reported that combined FO and LSIO controls would be introduced to more than 1,700 Kilmore properties, with some properties partly affected and others affected across the whole property depending on the flood data (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.145).

Modelling Architecture and Reliability

The model is built on a two-part hydrologic and hydraulic method: RORB was used for runoff and TUFLOW was used for two-dimensional hydraulic behaviour (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.6, 27). The hydraulic model covers approximately 2,500 hectares, uses a 3 metre grid, includes nested one-dimensional drainage elements, and represents Council’s underground drainage system and road drainage structures (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.27).

The study used 1 metre gridded LiDAR captured in 2009-10 as the base terrain dataset and verified it against 118 surveyed spot heights, finding that 85% of surveyed locations were within plus or minus 100 millimetres and that the average difference was -0.05 metres (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.9). Because LiDAR did not adequately represent Kilmore Creek bathymetry through the urban area, 12 surveyed cross-sections were captured between Green Street and Willowmavin Road to improve channel definition (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.9).

The main reliability limitation is calibration: there are no stream gauges on Kilmore Creek, and the 1992 event could not be assigned a design AEP because rainfall data was too distant and catchment conditions were unusually saturated (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.33-34). The study therefore validated flood behaviour against rational-method estimates, regional flood-frequency estimates, newspaper evidence, and community information rather than against a gauged historic flood hydrograph (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.17-20, 34-35).

The modelling sensitivity testing suggests the mapped 1% AEP extent is more sensitive to storage assumptions than to RORB kc or Manning’s roughness assumptions (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.36). In Scenario 1, the 1% AEP flood extent area was 5,549 square metres with 1,784 flooded properties, while reinstated storage reduced the extent area by 7.4% and reduced flooded properties by 0.5% (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.36). This matters because the model conservatively assumed storages were full before design events, while some retarding basins are designed to be empty before storms (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.33).

Flood Behaviour and Development Sensitivity

Flooding in Kilmore is generally confined along defined flow paths, including Kilmore Creek and other channelised drainage lines, rather than forming a broad regional floodplain across the whole township (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.39-41). In the 20% AEP event, flooding is largely contained within the creek and immediate floodplain, while rarer events progressively increase breakaway flooding around Curry Street to Bindley Court, Union Street between Andrew and Albert Streets, Powlett Street, and industrial land off the Northern Highway (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.39).

The developed-condition scenario increases flood levels and extents only modestly at the 1% AEP event, generally by 10 to 50 millimetres along main flow paths except for larger localised increases immediately upstream of blocked structures (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.39). Peak 1% AEP two-hour flows increase from 70.4 cubic metres per second to 75.0 cubic metres per second in Kilmore Creek, from 17.5 to 17.8 cubic metres per second in Ryans Creek, and remain at 20.9 cubic metres per second in Hamilton Creek under Scenario 2 (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.25).

The relatively modest developed-condition change is explained by catchment imperviousness: Kilmore Creek’s average impervious fraction increases from 13.0% to 17.2%, Ryans Creek’s increases from 6.8% to 7.4%, and Hamilton Creek remains at 5.8% under Scenario 2 (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.15). This means future development still matters locally, especially upstream of structures and drainage paths, but the study does not indicate a step-change in catchment outlet flows from the planning-scheme development scenario (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.15, 25, 39).

The property-exposure count is high even where over-floor damage risk is more selective because the mapping counts flooding within property boundaries above a 50 millimetre cut-off (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.40). Scenario 1 identifies 1,047 flooded properties in the 20% AEP event, 1,140 in the 10% AEP event, 1,268 in the 5% AEP event, 1,443 in the 2% AEP event, 1,578 in the 1% AEP event, 1,765 in the 0.5% AEP event, 1,948 in the 0.2% AEP event, 2,081 in the 0.1% AEP event, and 2,739 in the PMF event (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.41). Scenario 2 identifies 1,650 flooded properties in the 1% AEP event, compared with 1,578 under Scenario 1, indicating 72 additional properties with mapped boundary flooding under the developed-condition 1% AEP scenario (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.41).

Damage Economics and Public Infrastructure Exposure

The damages assessment uses the Rapid Appraisal Method and distinguishes building, agricultural, road-infrastructure and indirect damages (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.49-54). For the existing-condition 1% AEP event, building damages are estimated at 10.563 million, agricultural damages at 2,900, road infrastructure damages at 525,720, indirect damages at 3.328 million, and total damages at $14.419 million (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.54).

The study estimates total average annual damages for Kilmore at $1.625 million, largely due to building damage and particularly residential lots (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.54). The building-damage assumptions are conservative because the assessment uses the provided cadastre and planning scheme, including some lots classified as industrial or residential before they are actually developed (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.50).

Road exposure is material for emergency access and asset management because the 1% AEP event inundates an estimated 18 kilometres of road and generates estimated road damages of 525,720 (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.53). The PMF scenario increases road exposure to 54 kilometres and estimated road damages to 1.888 million, which indicates that rare-event transport disruption is a separate resilience issue from the more frequent local drainage nuisance areas (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.53).

Structural Mitigation: Five Concepts, No Tested Design Yet

The study identifies six flood-risk focus areas from consultation and modelling: Gehreys Lane upstream of Mollison Court, residential properties west of Mill Road between Gehreys Lane and Harrington Drive, Elms Boulevard and Willow Court, the Northern Highway-Mitchell Street intersection, the flow path north of Union Street between Albert and Andrew Streets, and the industrial area south of Willowmavin Road (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.56). These areas translate into five conceptual structural mitigation schemes, but the study states that the schemes had not been designed or tested in the hydraulic model at the conceptual stage (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.57).

Scheme 1 is the largest and most consequential concept because it combines open channels, culverts, retarding basins, pipe upgrades and possible Kilmore bypass road integration to address south-western Kilmore flooding around Gehreys Lane, Mollison Court, Mill Road, Curry Road and Harrington Drive (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.56-58). Scheme 1 has an estimated capital cost in the order of $6.0 million, may require land acquisition not included in the estimate, and would create ongoing retarding-basin maintenance obligations (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.58).

Scheme 2 proposes an open bypass channel along McIvors Road to divert overland flow away from The Elms Boulevard development and has an estimated capital cost in the order of 800,000 (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.58). Scheme 3 proposes repair and upgrade of the Mitchell Street bluestone drain and Melbourne Street culverts to match the capacity of outlet pipes under the Northern Highway, with an estimated capital cost in the order of 200,000 (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.59). Scheme 4 proposes Albert Street channel and pipe works with an estimated capital cost in the order of 50,000, but its effectiveness is limited by the existing underground pipe network running through private property and possibly under buildings (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.59). Scheme 5 proposes Willowmavin Road channel and Kilmore Creek culvert capacity upgrades with an estimated capital cost in the order of 650,000 and may require further private-business drainage works to fully address local flooding (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.59).

The planning implication is that the overlay amendment is the near-term implementable measure, while structural mitigation remains a capital-works investigation pathway subject to design, hydraulic testing, land access, environmental checks and funding decisions (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.57-59, 73). This sequencing matters because statutory controls can manage new development before mitigation works are delivered, but existing exposure remains unless warning, response, building-level and drainage measures are progressed (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.65-73).

Emergency Management and Flash-Flood Warning

Kilmore Creek is treated as a flash-flood catchment because response time is estimated at about 45 to 60 minutes under wet antecedent conditions and time to peak is estimated at about 3 to 6 hours (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.65). The study states that no flood warning system currently exists for Kilmore Creek, but that the project delivered inundation mapping, updated MFEP information, an indicative flood/no-flood guidance tool using publicly available rainfall data, and text for a Local Flood Guide (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.65).

The recommended warning system is deliberately low-complexity because the report concludes that investment in a more sophisticated forecast tool is probably not warranted given Kilmore’s relatively low flood risk (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.68). The recommended actions include seeking near real-time public access to the Willowmavin gauge, giving the flood/no-flood tool to the Kilmore VICSES Unit, considering a rain/river DipStik gauge in Apex Park, developing flood class levels if the gauge is installed, making flood maps and MFEP appendices available, completing the Local Flood Guide, and using community-facing awareness and social-media arrangements (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.67-71).

The emergency-management mechanism is therefore community interpretation rather than formal Bureau of Meteorology creek-specific forecasting (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.66-69). This has a direct planning consequence because land-use controls reduce future exposure, while warning and response measures reduce residual risk for existing properties already located in mapped flow paths (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.65-73).

Governance and Amendment Pathway

Goulburn Broken CMA identified Kilmore in a Mitchell Shire flood-risk assessment as needing flood overlay controls in the planning scheme, with land-use planning and municipal flood emergency planning both ranked as high priorities (Source: Mitchell Shire flood study summary.pdf, p.2). The same assessment recorded the Kilmore Flood Mapping and Intelligence Study as ongoing at that time and identified flash-flood warning services as a matter to be considered (Source: Mitchell Shire flood study summary.pdf, p.2).

By 2019-20, Goulburn Broken CMA’s annual reporting listed the Kilmore Flood Mapping and Intelligence Study as high priority and completed, with flood zone and overlay work completed and Council to prepare a planning scheme amendment (Source: Goulburn Broken CMA Annual Report 2019-20.pdf). By 2021-22, Goulburn Broken CMA’s annual reporting stated that Council would amend its planning scheme as part of a group amendment with Campaspe, Greater Shepparton, Murrindindi and Strathbogie councils (Source: Goulburn Broken CMA Annual Report 2021-22.pdf).

Council endorsed the Kilmore and Whiteheads Creek flood studies on 20 November 2023 and resolved to seek financial and resource assistance from the Department of Transport and Planning to implement the recommended planning scheme changes (Source: Mitchell Shire Council Meeting Minutes 20 November 2023.pdf, p.16). Council also resolved that if Victorian Government funding is not available, a further report will be required before undertaking the planning scheme amendment (Source: Mitchell Shire Council Meeting Minutes 20 November 2023.pdf, p.16).

The current amendment dependency is therefore external implementation support from DTP, not technical completion of the flood study (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.140-145; Source: Mitchell Shire Council Meeting Minutes 20 November 2023.pdf, p.16). Council’s own risk table identifies two high risks: updated flood data not reflected in the planning scheme, and flood data not being publicly available or incorporated into the planning scheme (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.144).

Current Status

As at the 20 November 2023 Council meeting, the Kilmore Flood Mapping and Intelligence Study had been completed, peer reviewed through Goulburn Broken CMA, endorsed by Council, and positioned for a future planning scheme amendment to implement FO and LSIO mapping (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.140-145; Source: Mitchell Shire Council Meeting Minutes 20 November 2023.pdf, p.16). The amendment had not yet been documented in the supplied corpus as authorised, exhibited, adopted, approved or gazetted (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.140-145).

Dependencies

  • Blocks: Full statutory transparency of mapped flood risk in Kilmore is blocked until the FO and LSIO amendment is prepared and progressed through the Victorian planning scheme amendment process (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.140-145).
  • Blocked by: The amendment pathway is dependent on DTP financial and resource assistance or, if that assistance is not available, a further Council report to commence the amendment (Source: Mitchell Shire Council Meeting Minutes 20 November 2023.pdf, p.16).
  • Informed by: The study is informed by RORB hydrology, TUFLOW hydraulics, LiDAR, targeted channel survey, Council drainage data, community flood evidence, damages assessment, and GBCMA peer review (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.6-10, 17-20, 27, 49-54; Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.144).
  • Implements: The amendment would implement floodplain-management policy requiring planning schemes to identify land affected by flooding, including the 1% AEP flood event or floodplain-management-authority determination (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, p.144).
  • Conflicts with: No direct policy conflict is evidenced in the supplied documents, but there is an implementation tension between the completed flood intelligence and the absence of current statutory controls in the Mitchell Planning Scheme (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.140, 144).

The flood study is cross-agency rather than purely local because it involves Mitchell Shire Council, DELWP/DTP, Goulburn Broken CMA, VICSES and the Bureau of Meteorology across planning, floodplain management and emergency-warning responsibilities (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.1, 65-71; Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.141-144). The Goulburn Broken CMA annual reporting places Kilmore within a broader regional flood-overlay implementation program involving other councils, including Campaspe, Greater Shepparton, Murrindindi and Strathbogie (Source: Goulburn Broken CMA Annual Report 2021-22.pdf).

Gaps in This Analysis

The corpus does not include the actual exhibited or draft planning scheme amendment documents, so the precise FO and LSIO schedule wording, map-sheet changes, notice requirements, submission issues and amendment lifecycle stage cannot be analysed (Source: Mitchell Shire Council Meeting Agenda 20 November 2023.pdf, pp.140-145). The corpus also does not include the full GIS overlay package, property-by-property flood level table, MFEP appendix, Local Flood Guide final publication, or any post-endorsement DTP correspondence, so this page cannot verify the exact parcel-level statutory effect or whether the warning-system recommendations have been implemented (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, pp.65-72). The structural mitigation options remain conceptual because the supplied report states that they had not been designed or hydraulically tested at the time of reporting (Source: Kilmore Flood Mapping and Intelligence Study_Final Report.pdf, p.57).

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