Introduction

Alternative

Flood Prevention Measures
With an attempt to increase the hydraulic capacity of the concerned section of the Shenzhen River within the Project Site, the following flood prevention measures have been considered during the preliminary feasibility study:

	Flood storage:	construct of flood storage tank / pond upstream or retardation pond along the relevant sections of the river;
	Flood diversion:	construct of a floodway to divert significant amount of rainwater away from the overflowed river; and
	River modification works:	such as river widening, elevation of river embankment and desilting works to increase the sectional area and hence the drainage capacity of the river.

A comparison of these flood prevention measures are summarized in the table below.

Flood Prevent Measures	Effect on Flood Prevention	Limitation	Recommendation
River modification works	Significant	Require additional land along the river	A combination of river widening, deepening and raising of river embankment is recommended

Flood Storage Pond along the river	Low – cannot attain the drainage capacity of a 50-year return period if use alone	Require additional land along the river	Could be used in conjunction with river modification works

Flood Storage Tank at upstream	Low/medium – cannot attain the drainage capacity of a 50-year return period if use alone	Involve construction works outside the relevant section of Shenzhen River; impacts on ecological resources and land resumption implication could be significant	Not recommended for this Project

Flood Diversion to outer tributaries	Significant	Involve construction works outside the relevant section of Shenzhen River; expensive; may involve change of landuse; impacts on ecological resources and land resumption implication could be significant	Not recommended for this Project

Based on the preliminary assessment of different flood prevention measures, a combination of river modification works and flood retardation pond was taken forward to study the preferred option for the Stage 4 regulation works.

..................................................................................................................................................................................................................

Design Options
An options evaluation exercise has been conducted with the purpose of identifying a technically feasible, cost-effective and environmentally & socially acceptable option of the Stage 4 regulation works.

The design principle of the works is to protect the livelihood of residents on both sides of the river with an ecological sensible design, which should maintain the naturalness of the river and riparian habitats and hence protect the biodiversity. The design and layout planning of the works should be compatible with the future LT/HYW BCP. Two design options were then developed for further study:

	Option A:	The existing profile of the concerned section of the Shenzhen River will be maintained as far as practical and massive excavation, dredging or filling will be avoided. Different designs such as trapezoidal, vertical or compound channel will be used with reference to the existing conditions. The centerline of the concerned section of the Shenzhen River will be about 4.5 km in length and a flood retardation pond will be constructed with a storage capacity of 80,000 m3. The river side slope will be at the ratio of 1:1.2 to 1:1.5 and the standard bottom width of the riverbed will be in a range of 14 to 32m.
	Option B:	The concerned sections of the Shenzhen River will be straightened and widened. The centerline of the concerned section of the Shenzhen River will be about 4.5 km in length and a flood retardation pond will be constructed with a storage capacity of 80,000 m3. The regulation works will mainly in the form of trapezoid open channel with side slope at the ratio of 1: 3. The standard bottom width of riverbed will be in a range of 14 to 16m.

The tables below provide an evaluation of the design options and the environmental benefits and dis-benefits of the options. Option A was chosen as the preferred option.

Issue / Criteria	Option A	Option B	Preferred Option
Land Requirement	29 ha of which 44% in Shenzhen side and 56% in Hong Kong side	31 ha of which 41% in Shenzhen side and 59% in Hong Kong side	Option A

Environmental Consideration - Ecological Friendly Design	Minimize the alteration of the existing river alignment; provides diversified river and riparian habitats to support the local ecology along the modification section	Widening, straightening and sectional modification of the relevant river section; will provide similar river and riparian habitats along the modification section	Option A

Environmental Consideration - Fill Balance	About 0.508 Mm3 surplus materials required off-site disposal	About 0.508 Mm3 surplus materials required off-site disposal	No significant difference (but less earthwork for Option A)

Environmental Consideration - Air and Noise Impacts during Construction	Less construction plants needed and hence less air and noise impacts during construction	More construction plants needed and hence more air and noise impacts during construction	Option A

Environmental Consideration - Landscape and Visual Impacts	Minimize the alternation of the river and hence preserve the existing landscape character area.	Extensive modification works will cause permanent loss of existing landscape character area	Option A

Management and Maintenance during operation	Management and maintenance would be simple and in low costs	Management and maintenance would be simple and in low costs	Same

Cost	586.9 million	608.8 million	Option A

Options	Environmental Benefits	Environmental Dis-Benefits
A	Follow the existing alignment as much as possible and hence preserve the existing landscape character better Less earthworks (excavation and fill) required and thus use less construction plant and hence less dust and noise impact Smaller land requirement area which means less direct impact on existing habitat	Will disturb the existing habitat but the impact will be localised Nuisance during construction period but will be mitigatable

B		Will disturb the existing habitat but the impact will be localised Nuisance during construction period but will be mitigatable More earthworks required Use more construction plant and hence more dust and noise impact More habitat loss