GLS CONSULTING ENGINEERING REPORT: DEVELOPMENT ERF 1692, FRANSCHHOEK: CAPACITY ANALYSIS OF THE BULK WATER & SEWER SERVICES

Transcription

1 GLS CONSULTING ENGINEERING REPORT: DEVELOPMENT ERF 1692, FRANSCHHOEK: CAPACITY ANALYSIS OF THE BULK WATER & SEWER SERVICES

2 12 March 2018 Lyners Consulting Engineers (Pty) Ltd P.O. Box 79 Main Street PAARL 7622 Attention: Mr Rudolph Schoonwinkel Dear Sir DEVELOPMENT ERF 1692, FRANSCHHOEK: CAPACITY ANALYSIS OF THE BULK WATER & SEWER SERVICES Your request regarding comments on the bulk water and sewer supply to the development (proposed development on Erf 1692, Franschhoek), refers. This document should inter alia be read in conjunction with the Water Master Plan (performed for the Stellenbosch Municipality) dated June 2017 and the Sewer Master Plan dated June The proposed development was not taken into consideration for the June 2017 master plans for the water and sewer networks. 1. WATER DISTRIBUTION SYSTEM 1.1 Distribution zone The master planning indicated that the proposed development area should be accommodated in the existing Franschhoek reservoir zone. The connection to the existing system should be done to the existing 100 mm diameter pipe in Reservoir Street, as shown on Figure 1 attached. The proposed development is situated inside the water priority area. 1.2 Water demand No provision was made in the existing Franschhoek Water Master Plan for any development on Erf For this re-analysis, the potential annual average daily demand (AADD) and fire flows for the proposed development area was calculated as follows: 28 Residential 0,6 kl/d/unit = 16,8 kl/d 46 0,4 kl/d/unit = 18,4 kl/d 370 m 2 commercial 0,4 kl/d/100 m 2 = 1,5 kl/d Total = 36,7 kl/d Fire flow criteria (Moderate risk) = m GLS Consulting (Pty) Ltd T F Elektron Street, Techno Park, Stellenbosch, 7600 PO Box 814, Stellenbosch, 7599, South Africa Reg no: 2007/003039/07 a member of the EOH Group of Companies Directors: A Bohbot, JW King, Z Mayet, BF Loubser, JJ Streicher and LC Geustyn

3 1.3. Present situation Network conveyance The existing 100 mm diameter pipe in Reservoir Street is currently supplied with water from the Franschhoek reservoir. The pipe network in the area can however also be supplied with water from the Shepperdson booster pump station. The pump station is currently bypassed and supplied directly with water from the Franschhoek reservoir zone. It is recommended that the following network upgrades are implemented to improve network conveyance to the proposed development area: Network upgrade Item 1 : 40 m x 160 mm Ø replace existing 100 mm Ø pipe R * Item 2 : 60 m x 160 mm Ø replace existing 75 mm Ø pipe R * Item 3 : 140 m x 110 mm Ø replace existing 75 mm Ø pipe R * Item 4 : 100 m x 110 mm Ø new inter-connection pipe R * Total R * (* Including P & G, Contingencies and Fees, but excluding VAT - Year 2017/18 Rand Value. This is a rough estimate, which does not include major unforeseen costs). Pressure During peak demand conditions the Energy Grade Line (EGL) at the proposed development is 343 m. This means that at the highest point of the development ( m contour) the head will be 23 m during peak demand conditions. If the higher lying areas experience low pressures during peak demand conditions it is recommended that an internal booster pump station be installed for the higher lying area of the proposed development. Reservoir capacity The criteria for total reservoir volume used in the Stellenbosch Municipality Water Master Plan is 48 hours of the AADD (of the reservoir supply zone). The existing reservoir volume available at the Franschhoek reservoir is sufficient to accommodate the proposed development. 2. SEWER NETWORK 2.1 Drainage area The development falls within the Wemmershoek Waste Water Treatment Plant (WWTP) drainage area. The recommended position for the sewer connection for the proposed development is at the existing 160 mm diameter outfall sewer in Reservoir Street, as shown on Figure 2 attached. The development is inside the sewer priority area. 2.2 Sewer flow No provision was made in the existing Franschhoek Sewer Master Plan for any development on Erf For this re-analysis, the peak day dry weather flow (PDDWF) for the proposed development was calculated as 25,7 kl/d.

4 2.3 Present situation The existing sewer system has sufficient capacity to accommodate the proposed development. No invert data was however available for a section of the outfall sewer downstream of the proposed development and it is proposed that the invert levels of this section of the main outfall sewer should be surveyed (as shown on Figure 2) to verify the that the existing system has sufficient spare capacity available to accommodate the proposed development. 3. CONCLUSION The developer of Erf 1692 in Franschhoek may be liable for the payment of a Development Contribution (as calculated by Stellenbosch Municipality) for bulk water and sewer infrastructure as per Council Policy. The existing water system has insufficient spare capacity available to accommodate the proposed development. The minimum upgrades required in order to accommodate the proposed development in the existing water system are master plan items 1 to 4 in order to improve network conveyance to the proposed development area. Peak demand pressure at the highest point of the proposed development is only 23 m and should the higher lying areas of the development experience low pressures it is recommended that an internal booster pump station be installed. The existing sewer system has sufficient capacity to accommodate the proposed development. It is however recommended that a section of the main outfall sewer be surveyed in order to verify that there is adequate spare capacity available to accommodate the proposed development. We trust you find this of value. Yours sincerely GLS CONSULTING (PTY) LTD REG. NO.: 2007/003039/07 Per: PC DU PLESSIS cc. The Director Directorate: Public Works Stellenbosch Municipality P. O. Box 17 STELLENBOSCH 7599 Attention: Mr Adriaan Kurtz

5 75 Ø Item 2 Legend Franschhoek reservoir zone Franschhoek Estate (private pipes) Raw water pipe Internal pipes (schematically) Master plan pipes Existing reservoir Existing pump station Existing PRV Proposed development Proposed Development Connect to 110 Ø 75 Ø Connect to existing pipe 75 Ø 200 Ø Shepperdson PS 33 44m 200 Ø Item 1 HEIDE Item Ø Connect to existing 75 Ø pipe Item Ø Connect to existing pipe Ø March 2018 Development : Erf 1692, Franschhoek Figure 1 Proposed Development Erf 1692 Franschhoek Existing Water System

6 Legend Existing sewer system Existing private pipes Existing pipes to be surveyed Internal pipes (schematically) 270 DIRKIE UYS Proposed Development LOUIS BOTHA KRUGER RESERVOIR Connect to VAN WYK HEIDE 270 UNIE AKADEMIE VAN RIEBEECK AALWYN ERIKA 330 BERG PROTEA March 2018 Development : Erf 1692, Franschhoek Figure 2 Proposed Development Erf 1692 Franschhoek Existing Sewer System