Augusta Street Group Special Charge Scheme, Mount Martha

The sedimentation of Balcombe Creek is a well-documented and significant issue for the aquatic ecosystem. Below are two studies commissioned by the Shire and delivered in 2017. The ‘Alluvium’ study was conducted by The University of Melbourne, retrieved core samples of sediment from Balcombe Estuary for analysis and reviewed historical aerial photos of the Estuary to review how it changed over time. This study focused more on the Estuary (rather than the creek further upstream) and on the impact of sedimentation.

The ‘CAPIM’ study was also conducted by the University of Melbourne, and investigated sediment loads and water quality at multiple sites in the Estuary and Creek. In the second stage of this study the focus was narrowed to assess stormwater flows at three sites, including the Augusta Street outfall.

Both studies are available here.

Alluvium-Balcombe-Estuary-sediment-history-July2017.pdf(PDF, 4MB)

CAPIM-Report-Balcome-Creek-July-2017.pdf(PDF, 4MB)

Brief study summaries

Alluvium

This study describes the layers of the core samples, with the oldest (deepest) layers dating back approximately 7,000 years, and reviewed historical aerial photography of the Estuary to asses the changes over some 40 years. Evident in the core sample layers is a sea grass bed that has been smothered by sediment within the last 80 years (i.e. following European settlement and the introduction of agricultural practices within the catchment). The islands within the estuary that are exposed at low water levels are built by sedimentation and the bayhead delta at the Henley Avenue outfall has grown from sedimentation. The core samples show coarse material (gravel) in the upper layers deposited from local urban subcatchments during storm events.

The Augusta Street area is not mentioned in this study as the outfall for these roads is further upstream from the study area in Balcombe Creek. However, the study is important to this proposal as the CAPIM study demonstrates that the Augusta St outfall contributes high sediment loads into the Creek that becomes the Estuary. Fine sediment is suspended in water for longer periods than coarse particles (like gravel), so as the Creek flows into the Estuary and the water flow slows, the fine sediment is deposited.

While this study recommends sealing existing unsealed roads, it also recommends avoiding “curb and gutter arrangements” in favour of vegetated swales. It is important to note that this recommendation relates particularly to the Henley Avenue subcatchment (though it does also apply generally). The Henley Avenue subcatchment does not have the steep slopes and densely vegetated roadsides that the Augusta St Group has. Both of these factors are limitations on the use of swales, which is why the Augusta St Group concept plan includes kerb and channel drainage.

CAPIM

This study sampled 15 sites, from the mouth of the Estuary to where Balcombe Creek runs closest to Uralla Road, to prioritise sites with high sediment loads for further study. Three subcatchments were found to contribute substantial sediments loads to the estuary, being Ferrero Reserve, Henley Avenue, and Augusta Street (in that order).

The study states that sealing existing unsealed roads in the Augusta Street catchment may help alleviate stormwater sedimentation loads but goes on to caution of the impacts this would have on increased water flow rates. This is a well-understood function of underground drainage systems and water sensitive urban designs (please see the section below under ‘Treating the issue’) can be used to control the increased flow.

The CAPIM study describes the Augusta Street outfall as being not a major source of sediments and a lower priority. Is it important to note that this is in the context of the three outfall sites that were selected for further study because they contribute the highest sediment loads of the 15 sites initially considered. In other words, although the Augusta Street outfall contributes the least sediment of the three selected for further study, that still places it as the third highest of 15 sites in the Estuary and Creek.

Treating the issue

Removing a major source of sediment (i.e. the unsealed road surface) is expected to significantly reduce stormwater sediment loads. It has been demonstrated that unsealed roads produce up to 100 times more sediment in stormwater runoff than sealed roads¹.

The CAPIM study shows that the Ferrero/Hopetoun Creek and Henley Avenue subcatchments are a higher priority for treatment than the Augusta Street Group, and Council has acted according to that priority. A special charge scheme to construct Hopetoun Avenue was attempted in around 2008 and a gross pollutant trap (GPT) was installed to reduce sediment from the Henley Avenue subcatchment (as recommended in the CAPIM study). As discussed above, the conditions and technical limitations in the Augusta Street Group are not necessarily comparable to that of the Henley Avenue subcatchment, which is why the proposed treatment differs.

While sealing and properly draining the roads is expected to provide the greatest impact on sediment reduction, there are a range of other measures that may also be used both in the Augusta Street Group and other subcatchments. If this project does not proceed Shire officers will be exploring those other measures in greater detail, with a view to prioritising maximal sediment reduction versus costs.

Stormwater sediment also comes from other sources, so a large part of sediment reduction involves Water Sensitive Urban Design (WSUD). WSUD can be defined as designing works (buildings, developments, civil infrastructure) to minimise the impact on the surrounding environment. In practice, it can include many different types of techniques to reduce environmental impacts and depends greatly on local conditions, restrictions, the issue sought to be resolved, and where in the water cycle WSUD is to be used.

For road construction projects WSUD might including rain gardens in the road reserve, sediment ponds, wetlands, permeable surfaces, sediment traps in kerbs, and a range of other designs or products. The WSUD treatments used for this proposal can only be determined during detailed design (discussed further below), though the general aims are to further reduce sediment loads in the stormwater and control the rate of stormwater flow.

¹Blue Mountains Urban Runoff Control Program (BMURCP). 1999. Rainfall Simulation Trials Blue Mountains. University of Western Sydney Nepean, Hawkesbury-Nepean Catchment Management Trust, Engineering Report CE14.

The concept plan on display at the property owners information evening (available here(PDF, 4MB)) is intended to provide you with an idea of how the road may be constructed. It is not the final design and, if the project proceeds, Shire officers will be consulting you on the detailed design before it is finalised. We welcome your suggestions and try to incorporate them into the design wherever possible.

The footpath was a particular point of interest for many people – the side of the road that the footpath would be built has not been decided (let alone the precise location relative to vegetation, driveways, etc.). Figuring out the best location for a footpath will require a detailed feature survey, which typically only happens as part of detailed design. Again, we will certainly be consulting you on this should the project go ahead.

The above is also true for other details such as crossovers, the location of drainage pits, the location and type of traffic calming devices, and many other things.

Retaining vegetation is a key goal of Mornington Peninsula Shire’s civil designers. Every effort is made to retain vegetation, though some vegetation removal is unavoidable. The extent of removal is usually lower than most people tend to expect, because the existing open swale drains are typically wider (and generally cannot be driven in) than rollover kerb (which is design be driven on). The footprint (or total width) of the constructed road is usually similar to the existing unsealed road however, the trafficable width (what you can safely drive on without getting stuck in a drain) of the sealed road is wider.

Below is a cross section diagram that shows the difference between the two types of roads. For ease of comparison, the trafficable width of both roads has been set to 5.5 metres. The unsealed road drawing is not necessarily representative of all existing conditions in the Augusta Street Group as the road widths vary depending on the location.

ASPHALT-AND-CRUSHED-ROCK-ROAD-SECTIONS.pdf(PDF, 236KB)

Total project cost estimate

Total project costs must be estimated at an early stage for all special charge schemes as this is a requirement of the legislated process for declaring a scheme. The estimate is provided by internal or external design engineers, civil works project managers, and quantity surveyors. It is based on the costs of recent similar works and projected costs. It is not possible to conduct an open tender for submissions from civil works companies at this stage, as the works are not fully designed nor is it even known yet if the project will go ahead.

After a special charge scheme project has been declared by Council (i.e. a final decision to deliver the project has been made by Council), the works are subject to a competitive public tender. This means that Council is able to achieve the best market price for the construction contract. If the total cost of the project is less than the estimate, the special charges paid by property owners are reduced (and there is no limit to the reduction). If the total cost of the project is more than the estimate, the special charges paid by property owners cannot increase by more than 10%.

Council's contribution

Council’s adopted policy for special charge schemes (available here) sets the proportion that it will contribute to special charge scheme projects of various types. The usual contribution to ‘Council initiated schemes’ (like this one) is 35% of total costs. It is only when a project provides significant, higher than usual, benefits to the broader community that Council will consider increasing its contribution to 50%, as in this case.

The presence of broader community benefits does not mean that there are no special benefits to property owners, and this is why special charges are still applied. The construction of local roads is not funded from general rates, and this has been the case for well over 100 years. In modern times developers are required to construct the infrastructure to service the land they wish to develop and sell however, Council’s have not always had the power to require this. If a road later requires upgrading, special charge schemes (known by other names through history, though retaining the same premise) have always been used throughout Victoria to fund those upgrades; the earliest Victorian example we are aware of is from 1867. The vast majority of sealed local roads on the Mornington Peninsula were paid for by the property owners that benefited from the roads, whether they were the developer or collective individual purchasers after development.

Affordability

Special charges may be paid in instalments over a period of up to 15 years, depending on the value of the charge. See the bottom of page seven of the Policy (linked above) for details on the terms.

Property owners experiencing financial hardship may apply for consideration under Council’s Financial Hardship Policy. Applications are assessed on a case-by-case basis and can be submitted only after a payment notice has been received.

The steps required for a special charge scheme can be grouped into two main categories: the statutory process, and additional consultation.

The statutory process includes all the steps required by Victorian legislation. The act and specific sections that apply are detailed in Council's Infrastructure Works Special Charge Schemes Policy. The statutory process must be observed by Council for the special charge scheme to be valid, which means that it cannot be altered or deviated from at Council’s discretion.

The additional consultation steps that Council undertakes are not required by the legislation, but they help to better inform councillors when making decisions on the proposed scheme. These steps are not required for the scheme to be legally valid, though Council’s view is that good community consultation is very important.

The entire special charge scheme process, additional consultation and statutory process, is set out in Council’s Policy (linked above) so that it is transparent and members of the community may know what to expect when participating in a scheme proposal.

Council meeting documents containing reports on this project may be found here:

Council Meeting Agenda - 5 September 2023 - see item 4.1 on page 11, under Management Reports, Planning and Infrastructure

Council Meeting Minutes - 5 September 2023- see page 12 for Council's decision.

It is Council’s job to balance the preferences of residents with its obligation to the wider community to protect the natural environment.

Special charge scheme caselaw demonstrates a general principle that enhanced services and amenity (e.g. a sealed road that is safer, reduces dust; underground drainage reducing localised flooding, puddles and mud; a footpath for safer pedestrian access, etc.) usually enhances the value of the land serviced, especially for residential land. That is to say that the open market tends to prefer sealed roads, formal drainage systems, and pedestrian facilities in residential areas even where some buyers do not share that preference.

Similarly, caselaw shows that the special benefit provided by the proposed works must be assessed objectively and is not reliant on the personal opinion or preferences of the property owner. This means that the improved amenity, safer access, reduced dust, improved drainage, etc. still provides a special benefit even if an individual would rather retain the unsealed road.

This is not to say that individual preferences are not valid – they certainly are, and the Council is required to consider every submission to a special charge scheme proposal when making a decision.