3.2 PROPOSED DAM EXTENSION - LOT 29 (NO. 531) BERRY ROAD, GIDGEGANNUP
(Gidgegannup) (Development Services)
KEY ISSUES
• The applicant is seeking approval for extension of an existing on-stream dam with a maximum capacity of 47,843m3.
• The applicant maintains that the existing dam and the proposed extension are more appropriately classified as a 'catchment dam' as opposed to an 'on stream' dam.
• Discussion with officers at the Department of Water supports the view of City staff that the dam is most appropriately defined as an 'on stream' dam. Based on the foregoing, assessment of the proposal in accordance with the City's Dam Policy (Po-C-089) has classified the dam extension as being of potentially 'high impact'.
• The dam design and construction is not in accordance with standards of the City's Engineering department guidelines for Small Rural Dams, capturing surface run off in excess of 25% of the catchment yield.
• The proposed increased capacity of the dam will allow for a continuation and increase in the obstruction of the stream flow and may have adverse impacts on both the down stream environs (ecosystem) and users.
• The proposal involves the removal of areas of vegetation to the south of the existing dam wall.
• The landowner advised that remedial works are required to reduce seepage and erosion of the existing dam wall. The increased dam capacity is to allow for revegetation of the property, establishment and maintenance of five hectares of lawn and gardens, revitalisation and expansion of the existing orchard, residential water use (unspecified) and stock water.
• The proposed end use of the extra water is for the establishment of extensive ornamental lawn and garden areas (total 3.55 hectares). It is considered that this is contrary to the intent and objectives of the General Rural area in preserving rural character of the area.
It is recommended that the Council refuse the proposed dam extension on the basis that the applicant has failed to provide the relevant information required by City's Dam Policy (Pol-C-89), namely a detailed and accurate hydrological assessment and structural details prepared by a suitably qualified engineer. In the absence of the foregoing information City staff are unable to make a thorough and informed assessment of the potential impacts associated with the obstruction of winter and summer flows on the downstream environment. Justification received from the applicant does not adequately demonstrate that the proposed capacity increase to the subject dam is integral to the function of an existing and approved rural activity
undertaken from the subject lot.
DETAILS OF THE PROPOSAL
The proposal involves the extension of a pre-existing 24,321m3 below ground, on- stream dam. The proposed development will increase the dam size to a total length of approximately 180 metres, up to 90 metres wide and 12 metres deep. The area of extension allows for an increased capacity of 23,522kL and the inclusion of an "island"
within the dam design. The proposed dam extension will increase the total capacity of the dam to 47,843m3 with a wall height of approximately 8 metres from the nearest adjoining natural ground level.
The applicant asserts that the dam's southern embankments are eroding and that the extension is remedial works and the extra water is to be used for bush fire suppression, revegetation of native flora, revitalisation of orchard and for the establishment and reticulation of five hectares of lawn and gardens and residential use.
Assessment of the proposed extension was undertaken in accordance with the City's Dam Policy (Pol-C-089), which identified the dam as falling within the 'high impact' classification. Accordingly, the proposal was advertised with the erection of a sign on site, newspaper advertisement and direct contact to all residents within 200m of the subject lot's boundary lines.
DESCRIPTION OF SITE
The subject lot is approximately 49.8 hectares in size and is located on the south side of Berry Road. The property slopes away from the road towards a watercourse at the rear of the lot. The average slopes are 2.9%, however become steeper at the rear of the lot (22% on the north side of the watercourse and 19% on the south side).
Vegetation cover consists of nearly 4 hectares of abandoned orchard and the existing remnant vegetation which although not dense maintains good coverage of the majority of the lot, especially the steeper portions adjacent to the watercourse.
The dam is located approximately 600 metres to the south of Berry Road along the western boundary line.
At present the applicant has access to approximately 47,843 kilolitres of water from both the existing dam and bore water licence for 10,000 kL. The applicant also has access to three onsite water tanks each, with an estimated capacity 120,000 litres.
SITE HISTORY/PREVIOUS APPROVALS
26 May 1999: Advice from landowners (F & J Klashorst) that property no longer qualifies for urban farm rating as orchard was decommissioned (fruit trees ripped out) and sheep sold.
February 2002: Ancillary Accommodation approved August 2002: Shed approved
July 2006: Filling of land approved (to front of existing shed - for parking of machinery and play area for children)
6 September 2006: Change of Land Use - Distillery (approved by Council)
OTHER RELEVANT PREVIOUS DECISIONS OF COUNCIL
NilAPPLICANT'S SUBMISSION
• "The proposed extension is required to stabilise the eroding embankment along the southern wall of the existing dam, works are for remedial purposes only.
• The water captured as a result of the extension is to be used for bush fire suppression, native revegetation, revitalisation of the existing orchard and establishment of lawn and gardens (approximately five hectares).
Details provided indicate that the applicant wishes to expand the existing area of the orchard. Tree variety and the overall area are yet to be established.
• Increased capacity of the dam also goes towards the establishment of sustainable energy technologies of thermal heat exchange. This is to allow for the cooling and heating of space based on the thermal energy contained in the water body of the dam;
• The dam is located on a groundwater seepage line and is of a 'moderate impact'.
• The proposed island features included the area of extension are proposed to provide a habitat for birdlife. The applicant proposes to fence these areas off from predatory wildlife such as foxes.
• Removal remnant and riparian vegetation will be necessary to allow for the increased capacity of the dam.
• The dam wall needs to be strengthened to allow for machinery and trucks to traverse the embankment;
• The new dam wall and surrounding embankments will be stabilised using non erosive layers such as compacted gravel and compaction of clay material and establishment of native trees and grasses;
• The redesign of the dam would allow for the inclusion of an outlet flow, to release water both automatically when it reaches an optimum level and manually.
• The applicant has developed a three stage program to be implemented over the next eight (8) years, end date 2015, to allow for the development and establishment of the proposed gardens and orchard."
PUBLIC CONSULTATION
Under the City's Dam policy those assessed as having a potentially 'high impact' are required to undergo a 21 day advertising period including the erection of a sign on site for a period of three weeks, a newspaper advertisement and notification to the relevant departments, local interest groups and direct contact with all adjoining landowners within 200 metres (from the boundaries of the subject lot).
A total of four parties have lodged submissions. Two objections and two non- objections were received. Issues raised in the submissions are addressed in the body of the report.
CONSULTATION WITH OTHER AGENCIES AND/OR CONSULTANTS
Referral was undertaken to the Department of Water. The following comments were provided:
• The Department of Water are primarily concerned with the approval for the interference with beds and banks (beds & banks permit) and for the approval for the taking of water from the proposed dam.
• The Department does not control the size of dams, construction or safety issues.
However, they encourage dams to be of a reasonable size and that appropriate summer by-passes are installed to maintain flow, if any, to downstream properties.
• The application has been assessed as an 'on stream' dam;
• A copy of the applicant's initial application was provided to the City. The application indicates that the increased volume of water is required for the keeping of livestock (cattle), orchard maintenance and establishment, lawn and gardens.
REPORT
Use Class and Permissibility
The applicant has applied for construction and extension to an existing dam, classed as a 'use not listed under the City's Town Planning Scheme No.9. The foregoing use is classified as an ‘AA’ use in the General Rural zone. This means the use is not permitted unless special permission is granted by Council. Hence the application is presented for consideration by Council on its merit.
Zoning
The subject lot is located within the General Rural Zone, the City's Town Planning Scheme No.9 provide the objectives of the General Rural Zone under Clause 8.2.4 (2) of the Scheme that are relevant to this proposal are:
d) Protection of water quality and watercourses within existing and proposed water catchment areas.
Clause 8.3.5 (5) of the Scheme states that Council when considering development proposals under this paragraph (relating to dam construction) shall consider the following:
a) Impact on existing and future Water Authority of Western Australia surface catchment areas;
b) Impact on stream environments;
c) Water area and capacity;
d) Purpose of the dam;
e) Visual intrusion including embankment heights; and
f) Stability of the structure, and in that connection the need for structural engineering design or certification.
Dams Policy (Pol-C-089)
The City's "Dams" Policy ranks proposed dams according to a number of criteria including, location, and size, maintenance of natural flows, cumulative impacts and vegetation clearing. Assessment of the proposal in accordance with the foregoing policy resulted in a score of 15 (out of a possible 15) for the proposed dam extension.
Accordingly, the proposal was classified as having a ‘high impact’ potential.
The objectives of the City's "Dams" policy include:
• To ensure that dams do not have a significant negative impact on the environment;
• To ensure that dams are properly designed and constructed;
• To ensure that dam sizes relate to the capability and catchment of the site and the intended use.
The City's "Dams" policy states that dam constructed on watercourses impedes the natural base flow of water, specific rain events and may also have a tendency to cause erosion resulting in movement of sediment downstream. On-stream dams may also cause disturbance to fringing vegetation and fauna habitat and potentially deprive downstream users of water.
Dam Design & Construction
The proposed dam extension involves the realignment of the southern wall of the existing dam. The applicant maintains that the dam size will remain unchanged with a maximum length of 120 metres however the capacity will increase.
The exact methodology for construction has not been provided. The applicant has indicated that this will be established through an onsite geotechnical assessment to ascertain the acceptability of site conditions, once Council has reached a resolution. It should be noted that in this instance the existing dam has been present for approximately 30 years and provides a level of assurance regarding the ability of the site to allow for dam construction. However, it is further noted that the increased capacity will contribute to greater stress on the proposed dam wall and surrounding areas.
The proposed dam design involves the creation of an island which the applicant maintains is to allow for native fauna habitat establishment, principally ducks, to nest and contribute to ecological diversity on the subject site and the locality of Gidgegannup in general. It is the applicant's contention that the island will isolate the bird life from potential predators such as foxes.
On balance it is considered that the provision for an island within the dam design is an aesthetic feature of the proposed extension. It is conceivable that birdlife could be equally served through the establishment of suitable flora species to allow for protection from predatory wildlife.
It is recommended that should Council resolve to approve the proposed dam extension it is advised that the application be granted pending the submission and approval of the following items:
a) A redesign of the proposed dam configuration to omit the island feature; and b) A geotechnical and engineering report prepared by an appropriately qualified
professional prior to the commencement of any ground works.
Dam Capacity
The applicant proposes to increase the capacity of the dam by approximately 23,522 kilolitres, to a total capacity of 47, 843 kilolitres.
The City, as part of its suite of development and construction guidelines, provides design standards for Small Rural Dams - Construction Details and Requirements (STD- 80-1s, Amendment B). The foregoing standard provides a list of Minimum Engineering Requirements for Small Rural Dams including one at point six (6) which states the following:
"The capacity of the dam shall not exceed 25% of the catchment yield based on the average annual total winter rainfall of 500mm. This applies especially when the dam is constructed directly over an existing creek…"
It should be noted by the Council that the 25% maximum catchment yield (The average annual volume of run-off from a catchment) applies only to those dams classified as 'on-stream'. In this instance the City's records indicate that the subject dam is indeed located on an identified watercourse, a view that has been supported by the Department of Water.
The City's engineers undertook assessment to define catchment area and subsequently calculate the potential yield based on an average annual total winter rainfall of 500mm. These investigations found that the potential total catchment yield would be approximately 63,411m3.
The existing dam has the capacity to capture and hold a total of 24,321m3, being 38.3% of the potential total catchment yield. Were the City to approve the application to extend the existing dam to allow for the capture and storage of up to 47, 843m3 the applicant could be able to capture up to 75.4% of the total catchment yield.
The capture and detention of more than 25% of the total catchment yields means that downstream users are deprived of water resources and the reduced flow of streams and creeks contributes to the deterioration of stream ecosystems, riparian vegetation, fauna and aquatic life and biodiversity.
It is recommended that the subject application be refused and the applicant is encouraged to submit a revised design reducing the overall capacity of the dam in accordance with the City's design standard STD-81-1s (Rev B) for Small Dam Construction.
Water Use and Rights:
The applicant maintains that the increased volume of water is justifiable due to the demand for water on the subject lot. The table below provides a breakdown of the proposed uses. The applicant states that the proposed works including the orchard revitalisation and maintenance, planting of gardens and lawns will be staged over the next six to eight years.
WATER REQUIREMENT SCHEDULE Area Plant/crop
types Irrigated area Water
allocation Water budget New Main
residence and cottage
(existing)
Grass 2 ha 7,800kL/ha 15,600kL
Native shrubs
and gardens 0.55ha 5,200kL/ha 2,800kL
Orchard Citrus 2 ha 9,750kL/ha 19,500kL
Front entrance Grass & Trees 1 ha 7,800kL/ha 7,800kL Thermal heat exchange system - does require the use of a specified volume of water.
However requires a minimum depth of 2 metres to be maintained.
The City does not have the authority to determine the rights an individual or company may have to draw water either in terms of quantity or end use. In this vein the landowner has made application to the Department of Water (DoW) with respect to the drawing of water for the purpose of undertaking numerous agricultural and horticultural pursuits. The City has been advised that determination of this application will take place once the City has reached a resolution.
Notwithstanding the above, the intent of the applicant to use approximately 55% of the proposed dam capacity for the establishment and maintenance of extensive ornamental lawn and gardens over 3.55 hectares is considered to be at odds with the rural nature of the property and aims and objectives of the general rural zone.
Objections raised the issue of water from the dam being used in the distilling process, proposed in a previous application to the City. Should Council to resolve to approve the application it is considered appropriate that a condition be applied to alert the applicant of the potential hazard of using dam water for human consumption and use.
The applicant should be further advised that the re-establishment of the orchard has not been considered as part of this application and may require the approval of the City under Town Planning Scheme No.9.
Environmental Impacts:
The applicants maintain that the subject dam (existing and proposed) is not located on a watercourse but rather on a groundwater seepage line and is more appropriately classed as a catchment dam. Consequently the applicant maintains that there is minimal environmental impact associated with the proposed development.
City records indicate an identified stream traversing the subject lot leading to the dam from the north and another creek line originating to the south of the existing dam wall (refer to attachments). At present this line is broken, which may in part be due to the restricted flow of the stream caused by the current dam design, which does not incorporate an overflow or bypass around the dam to allow for continued flow of the stream and ensure water for the downstream properties. The applicant has indicated that water is only able to continue the down stream flow, when the dam exceeds its current capacity.
Dams act to control or obstruct the flow of water in order to create a supply of water and may either be on or off stream. An on stream dam, simply put, is one capable of being filled by the flow of a waterway. Many of the environmental impacts associated with dam construction come from changes in ecosystem hydrology, including the release of sediment, land clearing, alteration of aquatic species migration patterns, seepage, dam failure and changes in the water quality parameters including, nutrients, turbidity, salinity and pathogen levels.
The proposed extension does make provision to rectify this issue and allow for the implementation of a water outlet to maintain the flow of water year round in accordance with the Department of Water's, Water Quality Protection Note Dam Construction and Operation in Rural Areas provides direction on matters relating to dam placement and construction methods. However, given the increase in the amount of water able to be captured due to the increased capacity there is no assurance that down stream users will not be further deprived of water resources or that the impacts of the downstream environments will not be adversely affected.
It is recommended, that regardless of the final determination that the applicant be compelled to upgrade the dam to allow for continued flow through the implementation of an outlet valve to ensure seasonal flow and environmental health.
Removal of Riparian and Remnant Vegetation
The proposed realignment of the dam will require the removal and inundation of areas of remnant vegetation.
The subject lot has previously been used for rural purposes including an operational orchard, still evident in aerial photographs and indicated on the site plan (refer attachments), as well as for sheep grazing. Despite this, large areas of the subject lot
remain significantly vegetated, including the proposed area to the south of the existing dam (refer to attached photos).
Riparian vegetation is vegetation on land that adjoins, directly influences or is influenced by, a body of water. Locally, riparian vegetation can be degraded as a direct consequence of clearing or activities such as gravel extraction, cropping or unlimited stock access. At a catchment scale, changes in flow regimes can also affect riparian vegetation either directly by drowning, or indirectly through erosion and bank slumping.
The City's dam policy provides that where the removal of riparian vegetation is required the application will generally not be supported. The area of vegetation is to the south of the dam embankment and may more appropriately be classed as remanent vegetation. However, given that the present design of the dam seeks to obstruct the stream flow, it is difficult to quantify the impact that the removal of this vegetation may have.
Given the weight of evidence on the negative ecosystem impacts resultant from the removal of vegetation, the precautionary principle requires that decisions on clearing should be deferred until sufficient information is obtained to demonstrate no unacceptable environmental impacts will result, including biodiversity loss or land and water degradation. In this instance, no information has been provided in regards to the impacts that may occur as a result of the area of vegetation or as to the quality or species involved. Accordingly, it is recommended that no action be taken in regards to its removal without first substantiating its value and the potential impacts associated with it's removal.
However, should Council resolve to approve the subject application, it is recommended that the applicant be compelled to provide for the approval of the City a strategic revegetation plan for areas surrounding the dam and the stream and creek lines.
Furthermore, the applicant shall be advised that submission may need to be made to the Department of Environment for the removal of remanent vegetation.
Visual Amenity (embankment height)
The proposed extension will require reconstruction of the southern embankments to a finished ground level of 203 metres (AHD), a maximum 8 metres from the nearest adjoining natural ground level (195m AHD).
In terms of visual impact the most likely affects will be to the westerly adjoining property, where the proposed extension comes to within 5 metres of the property boundary. The adjoining landowner has provided a statement of no objection detailing that the works are required to stabilise the progressively eroding embankment and that they are in full support of the works.
In all other respects the proposal is unlikely to cause adverse visual impact as the dam is setback over 600 metres from the street front and there is significant fall in the land away from the road and remnant vegetation is present over the subject lot to screen the dam from view. The nearest building on the adjoining property is approximately 148 metres south west of the proposed dam wall. Aerial photography and onsite inspection confirms that significant areas of remanent vegetation may act to block any potential visual intrusion. Furthermore, the adjoining landowner provided a comment of no objection and was in fact in favour of the proposal.
Notwithstanding the above, should Council resolve to approve the application a condition should be applied requiring the applicant to provide landscaping to stabilise the embankment and provide effective screening of the embankment to the adjoining property.
OPTIONS AND IMPLICATIONS
Option 1: Council may approve the application for the proposed dam extension. In doing so the Council would set an undesirable precedent for oversize on-stream dams that have not met adequately demonstrated compliance with the City's "Dams" Policy (Pol-C-89) and that may contribute to the deterioration of downstream health and water access.
This is not the preferred option.
Implications: The applicant would be conferred the right to undertake construction of the proposed dam in accordance with the approved plans. Contrary to Council policy.
Option 2: Council may refuse the application finding that the applicant has failed to:
a) Demonstrate that the increased dam capacity is integral to the operation of an approved existing rural use operating from the subject lot; and
b) Adhere to the requirements of the City's Dam policy in providing the necessary technical information including a detailed hydrological assessment and structural engineers report.
Implications: The applicant would not be permitted to extend the existing dam. If aggrieved by the decision the applicant may have a right of appeal to the State Administrative Tribunal under the Planning & Development Act 2005. This is the preferred option.
CONCLUSION
The applicant is seeking approval for extension to an existing on stream dam.
Justification received indicates that the proposed works are required for remedial purposes of suring up the dam walls to reduce seepage and to allow for increased capacity of 23,522 kL (total 47,843 kL) to supply water for future development of the subject lot to include the establishing and maintaining of four hectares of turf and gardens, re-establishment of the disused orchard, revegetation of native flora and stock water.
The subject proposal was assessed as a being of 'high impact', a point of contention confirmed by the Department of Water. Accordingly the applicant was required to provide a detailed hydrological assessment addressing the potential impacts of increasing the capacity of the dam on the down stream environment and an engineer's report detailing the methodology of construction, stability and land capability. To date this information has not been submitted.
In the absence of the foregoing expert reports City officers have not reasonably been able to assess the extent of any potential impacts associated with the proposal on downstream environments. Justification received from the applicant with respect to the need for the increased capacity does not adequately demonstrate the proposed capacity increase is integral to the function of the property or an existing approved rural use.
Accordingly it is recommended that the application be refused.
ATTACHMENTS
Location Plan Site PlanDam Contours and Design (existing and proposed) Dam cross sections
Photos (available for viewing by Councillors (only) upon request at the Administration Centre)
Schedule of Submissions
STRATEGIC IMPLICATIONS
Gidgegannup Rural StrategySTATUTORY ENVIRONMENT
Town Planning and Development Act 2005 Town Planning Scheme No.9
Dams Policy (Pol-C-089)
FINANCIAL IMPLICATIONS
NilRECOMMENDATION
That the Council resolve to:1) Refuse the proposed dam extension as submitted on the following grounds:
a) The proposed dam is categorised as "High Impact" in accordance with Council's adopted Policy on "Dams" and the applicant has not submitted the necessary information required to accompany the application, specifically:
(i) A comprehensive hydrological report prepared by a suitable qualified hydrologist or engineer providing an assessment of how the structure will affect the summer and winter flow patterns and describe summer and winter flow management provisions.
(ii) Certified report on dam structure by a suitably qualified engineer.
b) In the absence of the above information Council cannot reasonably assess the extent of any impact of the proposal on the downstream environment as required by Council Policy.
c) The applicant has not provided sufficient justification that the increased capacity of the dam is integral to the function of existing approved rural uses operating on the subject lot as required by Council Policy.
2) Advise the applicant that Council is prepared to consider a new Development Application for the proposed dam extension that is accompanied by the necessary information detailed above.
MOTION that the Council resolve to:
1) Defer consideration of this matter to the next Ordinary Meeting of Council to be held on 17 October 2007 to allow the Applicant to provide a hydrologist's report.
2) Advise the Applicant to revise his application to comply with all relevant City policies.
3) Advise the Applicant to provide sufficient justification for the increased capacity of the dam, catchment area and water usage.
4) Record that the reason for changing the Recommendation is to ensure Council has followed due process.
(Cr Bailey - Cr Haynes) RESOLVED UNANIMOUSLY TO:
1) Defer consideration of this matter to the next Ordinary Meeting of Council to be held on 17 October 2007 to allow the Applicant to provide a hydrologist's report.
2) Advise the Applicant to revise his application to comply with all relevant City policies.
3) Advise the Applicant to provide sufficient justification for the increased capacity of the dam, catchment area and water usage.
4) Record that the reason for changing the Recommendation is to ensure Council has followed due process.
