Y E L L O W FUT U R E S LTD. Design Concept for Stormwater Drainage for KI Grand Baie Residences. August 2016

Transcription

1 Y E L L O W FUT U R E S LTD Design Concept for Storwater Drainage for KI Grand Baie Residences August Réy Ollier Street, Beau Bassin, MAURITIUS Tel: (230) Fax: (230) E-ail: adinistration@sjpce.co

2 KI Grand Baie Residences TABLE OF CONTENTS Page No. 1. Introduction Description of the Site Storwater Drainage Concept for the Proposed Developent Design Standards Drawings... 4 LIST OF FIGURES Figure 1: Location Plan... 1 Figure 2: Catchent Area... 2 LIST OF ANNEXES Annex 1 Annex 2 Annex 3 Annex 4 Correspondence with NDU Catchent Area Drainage Layout Drainage Calculations Design Concept for Drainage

3 KI Grand Baie Residences 1. Introduction This report deals with the concept adopted for the design of storwater drainage syste for the KI Grand Baie Residences at Pereybere. 2. Description of the Site The Site is located in Pereybere, Grand Baie in the District of Rivière du Repart and is accessible through the Mont Choisy Cap Malheureux Road B13. The site is deliited to the North by the B13 Road, to the West by the Pyndiah lane (untarred road) and to the East and South by residential clusters. The location plan is shown on Figure 1. N SITE Figure 1: Location Plan The land eararked for the developent is currently uncultivated vegetated land and is at an average height of a..s.l. Trial pits revealed that the water table is at an average depth of below existing ground level. The topography of the region is generally flat with a ild slope of 0.5% towards the sea in the North West direction. The corresponding catchent area is about 320,000 2 and is predoinantly residential. Overland flows generated within this catchent during rainfalls are channeled in the natural drainage path which borders the Pyndiah Lane. The storwater is discharged in the lagoon. The alignent of the drainage path is shown in Figure 2. Design Concept for Drainage 1

4 KI Grand Baie Residences SITE NATURAL DRAIN Catchent Area ~ 320,000 2 Figure 2: Catchent Area The NDU has recently upgraded the natural drain to alleviate flooding probles in the region. A reinforced concrete drain wide with depth varying between 0.6 to has been constructed along the natural drainage path. The drain works have however not been copleted; the crossing at the B13 road is still outstanding. We understand fro consultation with the NDU that this section had been delayed due to wayleave issues but is being considered for early ipleentation due to the nuerous water stagnation coplaints registered at their level. A copy of the correspondence is attached in Annex 1. Design Concept for Drainage 2

5 KI Grand Baie Residences 3. Storwater Drainage Concept for the Proposed Developent The approach adopted for the storwater anageent for this developent is based on the sustainable drainage syste. All storwater runoff fro the developent will be catered by the on-site drainage syste through the following design principles: 1. Runoff fro the roof tops will be collected into fibre glass tanks and kept for non-potable reuse such as irrigation and cleaning. Only excess flows will be diverted towards the storwater syste. 2. The area of hardened surfaces has been kept to a iniu. Parking area will not be tarred; the surface will be topped with crushed coral sand to enhance percolation thereby iniising surface runoff. 3. The ipervious clayey subsoil strata on the entire parking and landscaped areas will be replaced by free draining aterial to further iprove the percolation rate. 4. Excess storwater fro the roof tops and the site will be channelled into the infiltration basin located within site as shown in Drawing No L18, Annex 2. The basin has been designed to retain excess surface water runoff up to The drainage syste has been sized to cater for a rainfall event of 1:10 years as recoended in The Study of Land Drainage Systes of the Island of Mauritius Report. The drainage layout is attached. The overall ipact on this developent fro a drainage perspective will be positive since no additional storwater will discharge downstrea and the peak volue during stor events will be attenuated. The on-site storwater drainage syste has been designed based on the following paraeters and assuptions: Site area of 11,000 2 Runoff coefficient of the original unbuilt area: 0.35 Maxiu built-up area: 35.7% The run-off coefficient used to establish the volue of surface runoff generated fro heavy rainfall due to the hardened surfaces in the proposed developent is 0.79 The soakaway and infiltration basin is designed for a return period of 10 years. Design Concept for Drainage 3

6 KI Grand Baie Residences 4. Design Standards The following codes and publications have been used for the design of the drainage: BS EN 752 Drain and sewer systes outside buildings BS 8110 Structural Use of Concrete Study of Land Drainage Syste of the Island of Mauritius (April 2003) Drainage Manual by South African National Road Agency Planning Policy Guidance by Ministry of Housing and Lands. 5. Drawings The drawings showing the drainage layout and detailed design are herein annexed. Design Concept for Drainage 4

7 ANNEX 1 CORRESPONDENCE WITH THE NDU KI Grand Baie Residences

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9 ANNEX 2 CATCHMENT AREA KI Grand Baie Residences

10 N E W S 6 5 Pereybère de Dev Dev R = SITE (Titre) ) sure (Me H H CATCHMENT AREA:320,000² Rev. Rev. Date By Issue Date Description NOTES : Drawn Scale Checked Date Drawing Nuber Rev.

11 ANNEX 3 DRAINAGE LAYOUT KI Grand Baie Residences

12 s Ligne des Pa s Geoétrique E de la rg e W S N M ur en bé to n de - Cap Malheureux (B13) on bét Mur en béton Mur en 2.5 BL K OC A BLOCK H BLOCK E BLOCK D 1.5 BLOCK F BLOCK B BLOCK C SLIP LANE BLOCK G 1.5 INFILTRATION BASIN 1.5 WATCHMAN CABIN STOP PARKING AREA TECHNICAL AREA Réserves de 1.50 de large ho nt C isy Chein coun de 15' de large (4.57) Drain en béton CT Chein coun de 15' de large (4.57) BS CT Bin 12² STOP CE CE Rou te Mo CT NOTES : LEGEND CUT OFF FRENCH DRAIN BURIED PIPE Drawn INFILTRATION BASIN SOAKAWAY UNDER PARKING AREA Rev. By Date Description 2.0 Rev. Date Issue Checked Drawing Nuber Rev. Scale Date

13 ANNEX 4 DRAINAGE CALCULATIONS KI Grand Baie Residences

14 7, REMY OLLIER STREET, BEAU BASSIN, MAURITIUS TEL: (230) FAX: (230) Eail: Design Paraeters: PROJECT: KI GRAND BAIE RESIDENCES JOB REF: PART OF STRUCTURE: DESIGN PARAMETERS SHEET NO. 1 INFILTRATION POND DESIGN WHOLE CATCHMENT DRAWING REF: CALCULATION BY: S.M CHECKED BY: D.O L18 DESIGN PARAMETERS Return Period (yrs) 1:10 DATE AUGUST 2016 Run off Coefficient, C before developent Before Developent Shrubs and bushes After Developent C y 0.05 Plots: 1.00 Green C p 0.20 Areas: 0.35 C v Catchent TOTAL CATCHMENT Catchent Area ( 2 ) Hardened Surfaces Green Areas Run off Coefficient, C before Developent of Morcelleent Run off Coefficient, C after = = xAP xA G Developent of Morcelleent A P + A G Increase in Run off Coefficient, Ceq = 0.44 Ceq = C after developent C before developent due to hardened surface after developent The Infiltration Pond and Soakaway have however been designed to cater for the entire developent for a runoff coefficient of Note: Hardened surfaces include built up area of 35.7%, pool area, technical and service area, footpaths, etc

15 PROJECT: KI GRAND BAIE RESIDENCES JOB REF: , REMY OLLIER STREET, BEAU BASSIN, MAURITIUS TEL: (230) FAX: (230) Eail: PART OF STRUCTURE: SIZING OF INFILTRATION POND AND SOAKAWAY INFILTRATION POND DESIGN WHOLE CATCHMENT DRAWING REF: CALCULATION BY: S.M CHECKED BY: D.O L18 SHEET NO. 2 DATE AUGUST 2016 SIZING OF INFILTRATION POND & SOAKAWAY Soakaway Design: 1:10 Soakaway size ( 2 ): Length () Width () Depth, vertical () 1.00 Infiltration Area, ( 2 ): Soakaway walls Base area Total Infiltration Area ( 2 ) Volue ( 3 ): Soakaway (50%void ratio) Infiltration pond Design: Plane Depth () Inc. Depth, side slopes 2:1 () Longer Sides Slope Area ( 2 ) Shorter Sides Slope Area ( 2 ) Base Area ( 2 ) Total Infiltration Area ( 2 ) Volue storage capacity ( 3 ): x x INFILTRATION POND & SOAKAWAY Top Plan Surface Area ( 2 ) Base Plan Surface Area ( 2 ) Mean Surface Plan Area ( 2 ) Volue ( 3 ) Cobined Retention Area ( 2 ) Cobined Storage Capacity ( 3 ) Soakaway capacity are higher than the volue of surface water run off. Therefore, sizing is adequate.

16 PROJECT: KI GRAND BAIE RESIDENCES JOB REF: , REMY OLLIER STREET, BEAU BASSIN, MAURITIUS TEL: (230) FAX: (230) Eail: PART OF STRUCTURE: SIZING OF INFILTRATION POND AND SOAKAWAY INFILTRATION POND DESIGN WHOLE CATCHMENT DRAWING REF: CALCULATION BY: S.M CHECKED BY: D.O L18 SHEET NO. 3 DATE AUGUST 2016 DESIGN CALCULATION FOR VOLUME INFLOW TO INFILTRATION POND & SOAKAWAY CATCHMENT INFILTRATION POND & SOAKAWAY Return Period (yrs) 1:10 Catchent Area ( 2 ) Plots: 7600 Green A: Cobined Run off Coefficient, C 0.79 Longest Flowpath (L), k 1.00 Slope, S Tie of Concentration, Tc (hrs) 0.51 Rainfall Intensity, I (/hr) 109 Peak Inflow, Q ( 3 /s) A P A G Soil Infiltration Rate, Q (/hr) Soakaway Design: Soakaway Surface Area ( 2 ) Storage capacity ( 3 ) (Including 50% void ratio) Case 1: Stor Duration = 1hr Rainfall Intensity, i (/hr) Run off Inflow ( 3 /hr) Infiltration Outflow ( 3 /hr) Required Storage ( 3 /hr) Case 2: Stor Duration = 24hrs Total Rainfall (/day) Run off Inflow ( 3 /day) Infiltration Outflow ( 3 /day) Required Storage ( 3 /day) Capacity of Infiltration Pond are higher than the volue of surface water run off. Therefore, sizing is adequate.