BASIC ASSESSMENT PROCESS FOR THE PROPOSED REHABILITATION AND - PowerPoint PPT Presentation

BASIC ASSESSMENT PROCESS FOR THE PROPOSED REHABILITATION AND ENGINEERING MEASURES AT THE BLUE GILL DAM, KEMPTON PARK GDARD REF. No.: 002/15-16/E0244 Public Meeting 14 March 2016 Slide 1

AGENDA 1. Welcome and introduction 2. Project Proposal and Rationale 3. BA process 4. Findings 5. Recommendations 6. Public consultation 7. Way forward 8. Discussion 9. Meeting close Slide 2

HOUSE ETIQUETTE • Language of choice • Work through the chair • Focus on EIA related issues • Equal participation • Identify yourselves prior to a question or comment • Wait until discussion session to ask questions • Cell phones off please Slide 3

PROJECT DETAILS • Project Proponent is the Ekurhuleni Metropolitan Municipality (EMM) – Mr. Swart, Chief Director – Roads and Stormwater • Project Engineer is CivEc • Environmental Assessment Practitioner is Mrs Jaana Ball • The site is located at Blue Gill Dam, Glen Marais within Erf 2255 (zoned PoS) • Off Veld Street, Kempton Park, Gauteng • Site is surrounded by the Blue Gill and The Waterfront Housing Estates (the Estates) • Located on an un-named non-perennial tributary of the Rietvlei system and in the quaternary catchment A21A of Crocodile- west and Marico Water Management Area • Proposed project is to be undertaken in a phased manner during the dry seasons of 2016 and 2017 Slide 4

PROJECT RATIONALE • The Dam has become so silted that stormwater is ‘backing up’ into the Quinine Street stormwater system reducing the capacity of that system • The temporary spillway bypass (trench) needs to be reinstated • Concern over the siltation levels reducing the volume of water the Dam can hold • Concern that the lower dam wall will break and result in loss of life and property damage • The Dam has become colonised by alien invasive plant species and has become unattractive aesthetically • Sewerage is periodically overtopping the manholes covers causing odours and an unsightly mess Slide 5

PROJECT ACTIVITIES The following engineering and rehabilitation activities are proposed: • Upgrade existing spillway (Phase 1) • Close and reinstate the temporary spillway bypass between the upper and lower dams (Phase 1) • De-silt the upper dam (Phase 1) • Repair erosion near the inlet culverts that are located underneath Veld Street (Phase 1) • Reinstate/ rehabilitate the upper Dam (Phase 1) • Repair lower dam wall (Phase 2) Note: Phase 1 – dry-season 2016 Phase 2 – dry-season 2017 Slide 6

ALTERNATIVES FOR THE UPGRADE TO THE EXISTING SPILLWAY The following upgrade alternatives for the existing spillway are being assessed: • Alternative 1: Lower the existing spillway by 1 m between the upper and lower dams • Alternative 2: Construct a second smaller spillway 1 m deeper than the existing one between the two dams • Alternative 3: Construct a pipe within the temporary spillway bypass between the two dams and reinstate • Alternative 4: Lower the existing spillway by 0.45 m between the two dams • Alternative 5: Construct a second smaller but 0.39 m deeper spillway than the existing one between the two dams Slide 7

PROPOSED CONSTRUCTION METHODOLOGY – Lowering of the spillway Existing spillway of the upper dam will be lowered by 0.45 m in order to lower the permanent water level in the dam so that it is 100 mm deep at the Veld Street culvert outlets Activities proposed:  Breaking of concrete across the full length of the existing concrete spillway crest, 6 m wide and approx. 760 mm deep to a new elevation level of 1603.350 m  Perpendicular saw cut along the outer face of the existing concrete apron for the secure construction and placement of a new Reno mattress structure  Construct a new 300 mm thick Reno mattress across the full length and width of the newly excavated concrete level in order to achieve a top of spillway level of 1603.650 m  BIDIM A5 to be placed behind and under all Reno mattresses  Finish off and fill gaps between outer face of the concrete apron and Reno mattresses with 25 MPa concrete Slide 8

Lowering of the spillway Slide 9

PROPOSED CONSTRUCTION METHODOLOGY – Desilting The upper dam will be de-silted and the surrounding area rehabilitated by completing the following activities: • Excavate material along the dam edges to achieve a 1:2 embankment slope along the edge of the dam – 17 m in (maximum reach of excavator) • In addition to the 17 m strip all the material in the upstream portion of the dam shown below will be de-silted. This will result in an uninterrupted body of water from the inlet to the spillway • Clean all hydraulic structures Slide 10

Desilting Slide 11

PROPOSED CONSTRUCTION METHODOLOGY – Construct the silt trap A silt trap will be constructed across the upper dam to facilitate future de-silting and to keep the balance of the dam clean. The following activities will be required: • Excavate the existing material 1 m wide to an elevation level of 1602.850 m • Construct and place a single row of gabion blocks, 1 m wide by 1 m long by 1 m high along new excavated trench • Place BIDIM A5 behind and under all gabion blocks Slide 12

PROPOSED CONSTRUCTION METHODOLOGY – Lower dam spillway The spillway of the lower dam will be rehabilitated as a second phase by replacing the existing concrete structure with a gabion structure Slide 13

BA PROCESS • Basic Assessment Process (and not Full EIA) required in terms of the National Environmental Management Act (NEMA 107 of 1998 (as amended) and EIA Regulations 2014 • Activity triggered within Listing Notice 1: GN. R 983, 8 Listing Notice 1: The infilling or depositing of any material of more than 5 cubic December 2014 Activity number 19. metres into, or the dredging, excavation, removal or moving of soil, sand, shells, shell grit, pebbles or rock of more than 5 cubic metres from- (i) A watercourse; (ii) The seashore; or (iii) The littoral active zone, an estuary or a distance of 100 metres inland of the high-water mark of the sea or an estuary, whichever distance is the greater- But excluding where such infilling, depositing, dredging, excavation, removal or moving- (a) Will occur behind a development setback; (b) Is for maintenance purposes undertaken in accordance with a maintenance management plan; or (c) Falls within the ambit of activity 21 in this Notice, in which case that activity applies. Slide 14

BASIC ASSESSMENT PROCESS The aim of the BA process is to: • Identify potential impacts (negative, positive and neutral) of the proposed rehabilitation and engineering activities, as well as cumulative impacts • Identify any potential mitigation measures/ management actions to avoid or reduce any potential negative impacts • Obtain the views and issues of Organs of State, as well Interested and Affected Parties (I&APs) Slide 15

BASIC ASSESSMENT PROCESS Pre-application activities • Site visit • Pre-Application Meeting with GDARD and record • Collect data, collate maps and plans, obtain consent from landowner, obtain declaration from Applicant and EAP • Appoint independent Freshwater Ecologist • Compile I&AP register • Distribute letter of notification and background information • Erect site notices • Place advert in local newspaper • Complete Draft Basic Assessment (BA) Report and Environmental Management Programme (EMPr), incl. Aquatic Ecology Study, and submit to GDARD, and make available to Organs of State and I&APs for 30-day Comment Period • Public meeting Slide 16

BASIC ASSESSMENT PROCESS Post application activities • Submit BA Application Form to GDARD • GDARD acknowledgement of receipt of Application • Incorporate public comments into Final BA Report • Amend documents based on comments received • Disseminate Final BA Report and EMPr (if required) • 30-day post application commenting period (if required) • Submit Final BA Report and EMPr to GDARD • GDARD commenting period and decision • Appeal Period • Work on site commences if decision is positive and no appeals/ appeals upheld Slide 17

BASIC ASSESSMENT PROCESS Outputs • Basic Assessment Application Form (standard format) • Basic Assessment Report (standard format) with appendices such as EAP details, PPP documentation, Correspondence with I&APs and GDARD • Aquatic Ecology Report • Draft Environmental Management Programme Slide 18

BA REPORT Key findings • Water Quality : The Dam is characterised by a circum-neutral pH with low salt loads. An increasing turbidity gradient exists from the inflow to the outflow, suggesting an increase in primary production and trophic status in the same direction • Diatoms: Diatoms comprise of species characteristic of alkaline, fresh-brackish, eutrophic waters with moderate oxygen levels. The downstream site sampled is less impacted compared to the upstream site. Diatoms comprised mostly of highly pollution tolerant species • Aquatic macroinvertebrates : System reflected a very low aquatic macroinvertebrate diversity and a high abundance of Chironomidae , indicative of a low oxygen environment and water that has a high level of pollution. A marginal increase in invertebrate diversity and sensitivity was noted along the longitudinal profile of the Dam • Fish: Fish community is transformed and dominated by introduced species. Three indigenous species, tolerant to changes in habitat, flow and water were sampled Slide 19 •