Coasts

Buying waterfront land to develop?

Be wary if you intend buying vacant waterfront land on which to build a house. When Council receives your building application, you might receive a letter saying something like

Your property is subject to Code E16.0 Coastal Erosion Hazard. Therefore, please provide a report from a suitably qualified person demonstrating that your proposed development will meet Performance Criteria E16.7 Development Standards.

This means that the property is within a Coastal Erosion Hazard band. See my Flowchart for applying the Tasmanian Coastal Erosion Hazard Code, posted in August 2016.

As a suitably qualified person, I offer geotechnical investigations and reporting to address these Performance Criteria.

See my downloadable flowchart which sets out how to determine whether or not land is in a Coastal Erosion Hazard band, whether or not the Code applies, and what needs to be done if it is.

In response to Council’s request, a suitably qualified person (who incidentally is not defined in the Code) should first establish whether or not the banding is accurate (and if not, demonstrate why it is not), and then report on whether the Performance Criteria can be met.

Performance Criteria for a new house are:

(a)

Not increase the level of risk to the life of the users of the site or of hazard for adjoining or nearby properties or public infrastructure

(b)

Erosion risk from wave run-up, including impact and material suitability, may be mitigated to an acceptable level through structural or design methods used to avoid damage to, or loss of, buildings or works

(c)

Erosion risk is mitigated to an acceptable level through measures to modify the hazard where these measures are designed and certified by an engineer with suitable experience in coastal, civil and/or hydraulic engineering

(d)

Need for future remediation works is minimised

(e)

Health and safety of people is not placed at risk

(f)

Important natural features are adequately protected

(g)

Public foreshore access is not obstructed where the managing public authority requires it to continue to exist

(h)

Access to the site will not be lost or substantially compromised by expected future erosion whether on the proposed site or off-site

(i)

Provision of a developer contribution for required mitigation works consistent with any adopted Council Policy, prior to commencement of works

(j)

Not be located on an actively mobile landform

Meeting some of these requirements – particularly criteria (b) and (c) – may be costly. They may require geotechnical site investigations and engineering inputs.

It makes a lot of sense to check out these issues before you buy the land.

Be aware that some real estate agents are unaware of the Code.

There are other Codes which may also affect your decision to purchase. Those that I can help with are the On-site Wastewater Management Code, the Landslide Code, and the Acid Sulphate Soils Code. See my May 2016 news posts about them, and the accompanying flowcharts I’ve produced for them.

Again, you should check these out Codes and flowcharts before purchase. My strong suggestion is that in every contract to purchase land (wherever the land may be) you should insist that a clause is inserted which makes purchase by you subject to a satisfactory geotechnical report. Landslides, wastewater, coastal erosion, coastal inundation and a range of other issues (tunnel erosion, drainage, reactive soils, acid sulphate soils, etc) are all geotechnical in nature.

Groundwater in coastal sands

I have been investigating groundwater conditions in sandy coastlines since the early 1970s, and during that time have installed groundwater extraction systems for golf club irrigation at Seven Mile Beach and Greens Beach, for possible town water at Swansea, Greens Beach and Lady Barron, and for caravan parks and domestic supplies.

Some years ago I teamed up with Mark Hocking, a Victorian groundwater geologist with expertise in numeric computer modelling.  Mark’s model for Seven Mile Beach (commissioned by Clarence City Council) is a first for Tasmanian coastal sand aquifers, and can be used to investigate short-, medium- and long-term scenarios such as (but not limited to):

• which areas will flood under selected rainfall events?
• what will be the water table effects of reducing/increasing medium- or short-term rainfall?
• what water table changes can be expected under different sea level rise scenarios?
• what effects with changing vegetation patterns/revegetation/land clearing have on water tables?
• will sewering a coastal town mitigate groundwater effects of sea level change?
• what groundwater effects will result from coastal engineering structures employed to mitigate sea level rise?
• how effective will short-medium- and long-term groundwater pumping be in mitigating rising water tables caused by sea level change?

Any considerations about water tables and groundwater movement ought to be placed in context with other coastal management issues.

Shallow water tables in vulnerable coastal areas have been neglected when predicting flood scenarios under rising sea levels and high rainfall events. Both combine to exacerbate water table rise, so that coastal inundation maps predicting the extent of flood events may need to be revised for some areas. Mark and I organised a May 2013 presentation/discussion for engineers, researchers and planners which covered fundamental groundwater issues and predictive numeric computer models for such coasts.  Contact me for a pdf of the presentation.