Stellenbosch Viewsheds

Transcription

1 Stellenbosch Viewsheds Visibility Analysis: Methodology and Submission Report

2 Report: Visibility Analysis Methodology and Submission Report for Stellenbosch Viewsheds For inclusion in the Stellenbosch Municipality Heritage Inventory Prepared by: Viridian Consulting (Pty) Ltd for Liana Jansen August 2018 Viridian Consulting Landscape Architects: Contact information Principal Landscape Architect: René Maria Brett Landscape Technologist: Fioné Smit Office Landline / Admin Ezelle Miller ezelle@viridian.co.za i

3 Visual Study August 2018 Table of Contents 1. INTRODUCTION Purpose of this Report Terms of Reference 2 a.) Scope 2 b.) Assumptions 3 c.) Limitations 4 d.) Information at hand 4 1

4 Visual Study August Introduction Viridian Consulting Landscape Architects (hereafter Viridian/the Landscape Architect ) was approached by Liana Jansen on behalf of the Stellenbosch Municipality (hereafter the Client ) to produce Viewsheds for the Scenic Routes mapped in the Heritage Inventory of, and Management Plan for, the Tangible Heritage Resources in the Stellenbosch Municipality (hereafter The Project ) in August Purpose of this Report This report provides an overview of the scope and requirements of the brief; and aims to provide the project leader with enough information to take decisions based on the submission of the Visibility Analysis. The report includes the assumptions and limitations under which the work was undertaken and qualifies the deliverable in terms of the expectations outlined in the brief. 1.2 Terms of Reference a.) Scope The Client required high-level Visibility Analysis in the form of Viewsheds for the following Scenic Routes as per the Heritage Inventory, accessible as the Stellenbosch Heritage Inventory Online Map: Scenic Route Grading Length (lm) Bottelary: B1 Grade II 899 Bottelary: B2 Grade IIIb 4240 Bottelary: B3 Grade IIIa 1796 Bottelary: B4 Grade II 4862 Bottelary: B5 Grade IIIb 4012 Bottelary: B6 Grade IIIa 9465 Bottelary: B7 Grade IIIa 2130 Klapmuts & Krom River: KK1 Grade II 5287 Klapmuts & Krom River: KK2 Grade IIIa 4347 Klapmuts & Krom River: KK3 Grade IIIa 5059 Klapmuts & Krom River: KK4 Grade IIIa 3185 Klapmuts & Krom River: KK5 Grade II 3797 Klapmuts & Krom River: KK6 Grade II 1339 Eerste River Central & Helderberg: ER/C1 Grade IIIb 4280 Eerste River Central & Helderberg: ER/H1 Grade IIIa 4280 Eerste River Central & Helderberg: ER/H2 Grade IIIa 1470 Eerste River Central & Helderberg: ER/H3 Grade IIIa 6903 Eerste River Central & Helderberg: ER/H4 Grade II 3086 Eerste River Central & Helderberg: ER/H5 Grade II 7403 Jonkershoek: J1 Grade II 8543 Ida's Valley & Dwars River: I/DR1 Grade II Ida's Valley & Dwars River: I/DR2 Grade II 2055 Ida's Valley & Dwars River: I/DR3 Grade IIIa 3403 Franschoek: FH1 Grade IIIb 4371 Franschoek: FH2 Grade IIIa 1721 Franschoek: FH3 Grade IIIb 6582 Franschoek: FH4 Grade II 4872 Franschoek: FH5 Grade II 3012 Franschoek: FH6 Grade II 2669 Franschoek: FH7 Grade II The deliverables to be submitted as per the Fees Proposal are the following: Vector files delineating the combined Viewshed coverage of each Scenic route for further graphic and data processing by the Project Team. 2

5 Visual Study August 2018 The data supporting the combined Viewsheds in Keyhole Markup language (.kmz) format; this being the viewsheds generated every 200 m along the scenic routes. The total amount of viewsheds per Scenic route area grouping is specified below. Scenic Route Area Grouping Estimated no of Viewsheds Bottelary 137 Klapmuts & Krom River 115 Eerste River Central & Helderberg 120 Jonkershoek 43 Ida's Valley & Dwars River 84 Franschoek 193 Total 692* *This number is based on the calculations done prior to commencement of work the actual number of viewsheds may total slightly more or less than this number. b.) Assumptions Based on the information received and available at the time of the writing of this report and the creation of the Viewsheds, the following assumptions are made: Viewshed Parameters The Visibility Analysis is done for the benefit of understanding the nature and significance of the various Scenic Routes. For the purposes of this study, the assumption is that because the routes are based on those of vehicular roads - most receivers will access the views offered by Scenic Routes from a moving vehicle. In addition, the number of viewers accessing the views from a moving vehicle as a driver or a passenger will therefore also outnumber those of people on foot, whether mobile or stationary. For this reason, the height of the receiver above Natural Ground Level was assumed to be lower on average than the standard 1,8m commonly used to calculate viewsheds. The following lists the parameters used to produce the Viewsheds: Viewshed Parameter Value Transmitter Elevation 1,5 m above Ground Transmission angle range of -89,9 to Receiver Elevation 89,9 above the horizon, checked at natural ground level Atmospheric Correction View Radius 15 km Sample spacing 20 x 20 m Number of Viewsheds per Scenic Route Viewsheds were generated every 200 lm along the totality of the Scenic Routes. This density was decided on in collaboration with the Project team to generate accurate enough high-level viewsheds for the purposes of the current Project; as well as to match the budget available for the Visibility Analysis component. The assumption is that 200m will accommodate both a 2 3 second glance at a view for a driver, as well as more sustained and active looking at views from passengers or NMT commuters lasting up to 10 seconds. Accuracy of the GIS Software Global Mapper V18.2 was used to generate the Viewsheds. The assumption is that the data produced are accurate depictions of what the true scope of the Line of Site (LoS) is on the ground and in reality. For future Visibility Analysis, the authors encourage a more in-depth study to be considered by the 3

6 Visual Study August 2018 Stellenbosch Municipality this would include the use of the DEMSA2 dataset and an allocation of funds toward the specialist study for more accurate Viewsheds and a far more thorough Visibility Analysis. c.) Limitations Based on the information received and available at the time of the writing of this report and the creation of the Viewsheds, the following limitations apply to this study: The Visibility Analysis was conducted with a basic Digital Terrain Model (DTM) of the study area; this means that buildings, vegetation and other features on the earth s surface other than natural topography do not feature as visual barriers or obstructions during the calculation of the viewsheds. While the composite viewshed provides an estimation of all potential Lines of Sight (LoS) along the Scenic Route, it does not necessarily represent the viewshed of each individual point the data submitted does however remain in separate viewsheds with an opacity of 50 75%, showing areas that are covered by more than one viewshed overlapping to be more opaque, and areas with less overlap being more translucent, respectively. As this study needed to fulfil the requirements of a high-level viewshed Visibility Analysis only, both time- and budget-related constraints precluded the use of the DEMSA2 dataset (South Africa s singular and most accurate Digital Surface Model (DSM)). This has a significant effect on the absolute accuracy of finer-grained LoS and Visibility studies. The fineness of the Viewsheds are determined by the sample spacing. This is determined by available budget and timeframe constraints. A 20m by 20m sample was deemed fine enough for the purposes of this exercise. But if further studies are done to refine the Visibility analysis, a more human-related scale of 10m by 10m or less should be considered. The nature of this exercise did not include for cross-checking the accuracy and extents of Viewsheds with peers and/or site-visits. d.) Information at hand The following information was provided and available at the time of the writing of this report and the creation of the Viewsheds: Provided Access to the Stellenbosch Heritage Inventory Online Map Project Background and relevant information including: Keyhole Markup Language files of the Scenic Routes Keyhole Markup Language files of the Landscape Character Units directly associated with the Scenic Routes Available: The data required to conduct the high-level Visibility Analysis was available through the following platforms: Google Earth ASTER GDEM v2 Worldwide Elevation Data (1 arc-second Resolution) 4

7 Appendix 4: Viridian Visibility Analysis with the viewshed of each scenic route 1. Grade II Viewsheds Figure 1: Grade II Scenic Drive Blaauwklippen Road Figure 2: Grade II Annandale entering Helderberg

8 Figure 3: Grade II Jonkershoek Figure 4: Grade II Knorhoek Road

9 Figure 5: Grade II R44 from Klapmuts Figure 6: Grade II Stellenboschkloof Road

10 Figure 7: Grade II Bloomberg Drive Figure 8: Grade II Bethlehem Drive

11 Figure 9: Grade II Helshoogte Drive Figure 10: Grade II Excelsior Drive

12 Figure 11: Grade II Robertsvlei Drive (Franschhoek side) Figure 12: Grade II Hugenote Drive and Main Road

13 Figure 13: Grade II Olifantshoek Pass 2. Grade IIIa Viewsheds Figure 14: Grade IIIa R45 entering Franschhoek at La Motte

14 Figure 15: Grade IIIa R45 from Helshoogte Drive Figure 16: Grade IIIa Polkadraai entering Stellenbosch

15 Figure 16: Grade IIIa Baden Powell Drive Figure 17: Grade IIIa Klein Helderberg Drive

16 Figure 18: Grade IIIa Annandale Road Figure 19: Grade IIIa Unknown Road

17 Figure 20: Grade IIIa Winery Road Figure 21: Grade IIIa R44 from Somerset West

18 Figure 22: Grade IIIa R44 entering Stellenbosch from Klapmuts Figure 22: Grade IIIa Elsenburg

19 3. Grade IIIb Viewsheds Figure 23: Grade IIIa Kromme Rhee Figure 24: Grade IIIb Polkadraai Road entering Stellenbosch from Cape Town

20 Figure 25: Grade IIIb Devon Valley Road Figure 26: Grade IIIb R301 from Paarl

21 Figure 27: Grade IIIb Robertsvlei Road