Maximum loss rate of wet excavation should be kept at or below the limits adopted in the EIA Study.

Dry excavation will be used, as far as practicable, for cofferdam excavation.

Attention will be paid to the lifting speed of the grab to minimise the loss of sediment.

Excavated sediment will be disposed of in a gazetted marine disposal area in accordance with the Dumping at Sea Ordinance (DASO) permit conditions.

The marine vessels for transport of sediment to the marine dumping ground will be fitted with tight bottom seals in order to prevent leakage of material during transport. The barges will be filled to a level, which ensures that material does not spill over during transport to the disposal site and that adequate freeboard is maintained to ensure that the decks are not washed by wave action.

The contractor(s) will confirm that the works cause no visible foam, oil, grease, litter or other objectionable matter to be present in the water within and adjacent to the excavation site.

For concurrent excavation works at adjacent work areas (ie Work Areas I and II, and Work Areas III and IV), construction will be carried out along the same flow direction (ie from upstream to downstream / downstream to upstream) to minimise the overall impacts to SS concentrations from adjacent work areas.

Good construction site practices outlined in ProPECC PN 1/94 “Construction Site Drainage” should be followed as far as practicable in order to minimise surface runoff and the chance of erosion, and also to retain and reduce any suspended solids in surface runoff prior to discharge.

Excavation within cofferdam will be maintained in dry condition as far as possible. Water within the cofferdam will be discharged to the river before excavation commences and at times when needed (eg after heavy rain). Adequate time (48 hours) will be allowed for suspended solid to settle (potentially overnight) before foundation pit drainage are being discharged outside the works area.

Non-active area along the river bank will be covered by impermeable sheets or hydroseeding completed sections immediately whenever possible to minimise erosion of soil by runoff particularly during heavy rainstorms.

Appropriate surface drainage will be designed and provided, where necessary. In particular, surface runoff will be collected along the river bank and be diverted to sedimentation tank/pond before discharge into the river

Runoff from dredged sediment stockpile areas should be collected for treatment by sedimentation with the addition of settling agent. The treated water will be reuse on site for water spraying.

An adequate number of portable toilets should be provided for the on-site construction workforce. Wastewater/sewage will be transferred to the Luofang Sewage Treatment Works in Shenzhen (during the river modification and associated works) or a Government sewage treatment works in HKSAR (during the advanced works) by a reputable collector.

Debris and refuse generated on-site will be collected, handled and disposed of properly to avoid entering the nearby WSRs.  Stockpiles of cement and other construction materials will be kept covered when not being used.

Oil leakage or spillage will be contained and clean up immediately. Waste oil will be collected and stored for recycling or disposal in accordance with the Waste Disposal Ordinance.

The hydrodynamic modelling has predicted that the operation of the Project will be beneficial to the Project Site by improving its flood prevention performance and no adverse impacts to hydrodynamics are expected to occur at the sensitive receivers. The water quality of the Shenzhen River during the operation of the Project will be improved. Mitigation measures are thus not considered to be necessary.

Eroded sediment flowing from the Project Site will be deposited between Ping Yuen River confluence and Huanggong River confluence and consequently affecting the flood prevention performance of this section. Maintenance dredging, which would mainly be undertaken outside the Project Site, would be required to rectify the flood prevention performance. No adverse water quality impact due to maintenance dredging is predicted. Mitigation measures are not considered to be necessary.