Winding Creek detention basin GIS visualisation study · WINDING CREEK DETENTION BASIN GIS VISUALISATION STUDY FOR HUNTER WATER CORPORATION VERSION 1.0 2 2 Project scope 2.1 Project

Winding Creek detention basin GIS visualisation study

For Hunter Water Corporation February 2010

MANIDIS ROBERTS PTY LTD ABN 42 003 550 972

Level 9, 17 York Street, Sydney NSW 2000 GPO Box 91, Sydney NSW 2001

t (02) 9248 9800 f (02) 9248 9810 [email protected] www.manidisroberts.com.au

Quality control Our reference 09051 Version number 1.0 Date 22 February 2010

Contents 1 Executive summary 1

2 Project scope 2 2.1 Project background 2 2.2 Winding creek detention basin 2 2.3 Visual amenity issues of development 3 2.4 Project scope and understanding 4

3 Data review and modelling 5 3.1 Document and data review 5 3.2 Desktop viewshed analysis 5 3.3 Mapping 6

4 Receptor analysis 7 4.1 Winding Creek detention basin visual catchment generation 7 4.2 Residential receptor analysis 8 4.3 Road corridor receptor analysis 9

WINDING CREEK DETENTION BASIN GIS VISUALISATION STUDY FOR HUNTER WATER CORPORATION

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1 Executive summary

The Winding Creek detention basin was constructed in 1993 by Hunter Water to help alleviate flooding in the Winding Creek catchment. Hunter Water is responsible for maintaining the stability of the detention basin, particularly during extreme rainfall events.

Following a major storm event in 2001, investigations concluded that, in order to prevent the dam from overflowing and causing potential property damage, it would be necessary to strengthen the existing structure and upgrade the outlet capacity of the detention basin.

Hunter Water proposes to raise the height of the existing embankment by constructing a 1.5m wall along the embankment’s crest. The proposed wall will be a significant feature in the existing topography as it sits near the lowest point of a basin with elevation gradually increasing in the immediate surrounds.

The results of a GIS (geographical information system) visualisation study of Winding Creek’s 1.5m detention basin wall are summarised in a series of maps presented throughout this report. Large scale maps demonstrating the LiDAR-generated visual catchments over an aerial photography base have been generated using LiDAR first return data.

LiDAR-generated visual catchments show the detention basin wall will impact the visual amenity to some degree for up to twelve residents of Elizabeth Street, Gimbert Street and potentially Lewis Street in Cardiff South as well as several residents of Gillian Crescent in Cardiff.

In surrounding Cardiff South streets visibility from urban roads is greatest for nodes in the northern half of the wall and reduces steadily from node one through six. Nodes seven and eight are not visible from any local road. The cul-de-sac end of Gimbert Street provides an access point to the detention basin and overlooks the majority of the detention basin wall in a northeast-southwest alignment. The areas of road able to see both the fifth and sixth node along the detention basin wall are concentrated toward the end of Gimbert Street.


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2 Project scope

2.1 Project background

The Winding Creek detention basin was constructed in 1993 by Hunter Water to help alleviate flooding in the Winding Creek catchment. It is located next to Cardiff High School and local residences.

Hunter Water is responsible for maintaining the stability of the detention basin, particularly during extreme rainfall events. Following a major storm event in 2001, Hunter Water undertook extensive investigations to assess the capability of the structure to cope with such intense rainfall.

The investigation concluded that, in order to prevent the dam from overflowing and causing potential property damage, it would be necessary to strengthen the existing structure and upgrade the outlet capacity of the detention basin. Hunter Water proposes to raise the height of the existing embankment by constructing a 1.5m wall along the embankment’s crest.

2.2 Winding creek detention basin

The Winding Creek detention basin site is located between the suburbs of Cardiff and Cardiff South, 250m south of Cardiff High School. The basin wall will be constructed adjacent to Elizabeth and Lewis Streets in Cardiff South, as shown in Figures 1 and 2. The wall will be 300m long and 1.5m high.


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2.3 Visual amenity issues of development

The existing visual amenity of the Winding Creek catchment is of open grass directly abutted by pockets of vegetated marsh, sports fields and local bush reserve to the north, east and south. To the west the site runs adjacent to residential properties in Elizabeth Street and Lewis Street, separated by property fencing and residential landscaping.

The proposed wall will be a significant feature in the existing topography as it sits near the lowest point of a basin with elevation gradually increasing in the immediate surrounds. The detention basin wall will impact the visual amenity for users of Elizabeth Street, Gimbert Street and potentially Lewis Street in Cardiff South and may potentially be viewed from other roads in Cardiff, see Figure 3.


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2.4 Project scope and understanding

The visualisation study of the Winding Creek detention basin wall undertakes generation of an independent desktop assessment (using a geographical information system (GIS)) of the visual catchment of the proposed wall. The assessment will principally be carried out for the study area defined by Hunter Water Corporation in a one kilometre catchment around the proposed project site.


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3 Data review and modelling

A visualisation study is a desktop assessment using available elevation data, topography and imagery in a GIS. The visualisation study process undertaken for the Winding Creek detention basin is outlined below.

3.1 Document and data review

A desktop review is conducted of document and data resources relevant to the project. Review of relevant resources for the Winding Creek detention basin includes:

• Available aerial imagery and LiDAR data.

• Topographic, elevation point and contour data.

• Cadastral data relevant to identified receptors.

• Advised community boundaries for investigations, including study area of interest.

• Picture, drawings and artist’s impression of modelled detention basin provided by Hunter Water Corporation.

• Data pertaining to detention basin geometry and location, and of any related infrastructure.

• Reference material relating to the detention basin and preliminary environmental investigations.

3.2 Desktop viewshed analysis

Viewshed analysis is carried out within the study area provided to determine visual catchments for receptors for the Winding Creek detention basin wall. All viewshed analysis is conducted using GIS which enables:

• Terrain analysis.

• Grid and contour, grid mathematics.

• Generation of a digital elevation model (DEM) from elevation data. This is demonstrated in Figure 4.

• Extruding features (point to line/line to fence/polygon to solid).

• Generating landscape profile (longitudinal sections), showing ‘line of sight’ for receptors.

• LiDAR ground data merged with 25m digital terrain model.

• Raster sampling of LiDAR TIN at 1m pixel resolution.

• Calculating areas and volumes.

• Surface analysis – hill shade, slope, aspect – to investigate elevation and LiDAR correlation and any data anomalies.

For the purpose of analysis the detention basin wall is represented by eight nodes, every time there is a change in the curvature of the wall. Viewshed analysis will investigate any location that can see a part of the wall (that is detect one or more nodes of the wall).


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3.3 Mapping

Visual catchment maps will be prepared for the visible Winding Creek detention basin wall that will be developed from the viewshed analyses, undertaken for the proposed wall.


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4 Receptor analysis

4.1 Winding Creek detention basin visual catchment generation

Figure 5 represents the Winding Creek detention basin wall and nine nodes on the wall checked for visibility in the surrounding landscape. The area in green is lowland vegetation and marsh occurring below the level of the basin wall. Individual trees featuring in the landscape are marked with heights, as are stands of bush reserve around the site. The fence line depicted in red has not been captured by LiDAR data so it of unknown height and has effectively been excluded from the visualisation analysis.

Basin wall visibility is tested at nine nodes along the wall, numbered in Figure 5. A visual catchment generated for Winding Creek detention basin wall, using LiDAR first return data and GIS, indicates impacts to visual amenity are experienced mainly within the first few hundred metres of the basin wall. These findings are reflected in Figures 6a, 6b and 6c and are summarised in 250m intervals from the basin wall.

In Figure 6 green represents areas that can see part of the wall (one or more nodes). Visibility is concentrated within 250m of the detention basin wall. Within 250–500m from the detention basin wall rooftops and tree canopies are the main receptors. Visibility beyond 500m from the detention basin wall is very limited.


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4.2 Residential receptor analysis

Figure 6a shows the visual catchment analysis results on an aerial photography base and concordant with the features shown in Figure 5. Large scale maps demonstrating the LiDAR-generated visual catchments over an aerial photography base emphasise that visual receptors indicated from desktop analyses alone may include rooftops and tree tops and therefore may over-represent the actual number of residential receptors.

Figure 6a highlights the detention basin wall is visible from the sports fields, low-lying marsh and grass fields immediately surrounding the basin. The figure also highlights that beyond 250m from the detention basin rooftops and tree canopies are the main visual receptors detected by the LiDAR first return data.

Approximately twelve properties in Cardiff South have been identified as potentially sensitive receptors experiencing some degree of visual impact according to the viewshed analysis. These properties are concentrated in Gimbert, Elizabeth and Lewis Streets. Impact to visual amenity for these properties is detected from the canopies of landscape trees, rooftops as well as at ground level in places, where at least one node of the detention basin wall is visible. Visibility is interspersed around existing features in the residential environment.

Three of these properties In Elizabeth Street, directly south of Gimbert Street, have fencing between them and the basin wall that has not been captured in the LiDAR data (see Figure 5). These properties have elevations one to two metres higher than the detention basin (see Figure 3) so it is possible that fencing the same height (1.5m) or higher than the detention basin wall would mitigate detention basin wall visibility to some degree from ground level on these properties.


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Although elevation increases towards Cardiff, impact to visual amenity from constructing a detention basin wall are largely mitigated by the tall stand of trees buffering Gillian Crescent from the playing fields and Cardiff High School. There are potentially two or three sensitive receptors at different points in Gillian Crescent.

4.3 Road corridor receptor analysis

Cardiff South and Cardiff roads are used by local residents and people accessing recreational facilities in the neighbourhood. Although visibility of the detention basin wall is likely to be interrupted by urban buildings and landscaping, or experienced for only short periods of time while journeying along a road, an impact to visual experience of the neighbourhood can nevertheless be detected. Figure 6a represents in red areas of public roads experiencing some impact to visual amenity.

Figure 6b provides a breakdown on the contribution of each node to road visibility, or shows from nearby roads where each node is visible along the detention basin wall. Visibility from urban roads is greatest for nodes in the northern half of the wall and reduces steadily from node one through six. Nodes seven and eight are not visible from any local road.


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The cul-de-sac end of Gimbert Street provides an access point to the detention basin and its grassy surrounds. This area is slightly elevated to the basin, relatively clear of landscaping and overlooks the majority of the detention basin wall in a northeast-southwest alignment. The areas of road able to see both the fifth and sixth node along the detention basin wall are highlight in red in the following figure – the majority of these points fall within the end of Gimbert Street.


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Figure 6c demonstrates line of site analysis generated for public road receptor points in Sixth Street, Cardiff South as well as from the corner of Gillian Crescent in Cardiff, where green represents the visible path between the receptor and the detention basin wall and red represents the terrain not visible from the receptor.


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5 Conclusion

A visual catchment generated for Winding Creek detention basin wall, using LiDAR first return data and GIS, indicates impacts to visual amenity are experienced mainly within the first few hundred metres of the basin wall. Basin wall visibility is tested at nine nodes along the wall, from one in the northeast through to nine in the south.

Visualisation results show visibility is concentrated within 250m of the detention basin wall. Winding Creek detention basin wall is visible from the sports fields, low-lying marsh and grass fields immediately surrounding the basin. Within 250–500m from the detention basin wall rooftops and tree canopies are the main receptors. Visibility beyond 500m from the detention basin wall is very limited.

Approximately twelve properties in Cardiff South have been identified as potentially sensitive receptors experiencing some degree of visual impact according to the viewshed analysis. These properties are concentrated in Gimbert, Elizabeth and Lewis Streets. Three of these properties In Elizabeth Street, directly south of Gimbert Street, have fencing between them and the basin wall that has not been captured in the LiDAR data that may potentially mitigate detention basin wall visibility to some degree from ground level on these properties.

Although elevation increases towards Cardiff, impact to visual amenity from constructing a detention basin wall are largely mitigated by the tall stand of trees buffering Gillian Crescent from the playing fields and Cardiff High School. There are potentially two or three sensitive residential receptors at different points in Gillian Crescent and visibility from the open road at the corner of Gillian Crescent.

The cul-de-sac end of Gimbert Street provides an access point to the detention basin and overlooks the majority of the detention basin wall in a northeast-southwest alignment. The areas of road able to see both the fifth and sixth node along the detention basin wall are concentrated toward the end of Gimbert Street.

In surrounding Cardiff South visibility from urban roads is greatest for nodes in the northern half of the wall and reduces steadily from node one through six. Much of this visibility is interspersed with housing, vegetation and other elements of the urban landscape. Nodes seven and eight at the southern end of the detention basin wall are not visible from any local road.

Documents

Winding Creek detention basin GIS visualisation study · WINDING CREEK DETENTION BASIN GIS VISUALISATION STUDY FOR HUNTER WATER CORPORATION VERSION 1.0 2 2 Project scope 2.1 Project