Having won the fight to stop the construction of a railway viaduct through Long Valley, green groups now say the alternative tunnel option is not as environmentally friendly as it sounds, and want the viaduct back. The public will find the turnaround difficult to fathom. Environmentalists must now articulate their case clearly and cogently or the goodwill they have earned in putting up a spirited defence of the wetland will be lost. Their main contention is that an underground tunnel will have a higher construction bill and will also mean much higher operation costs for the railway. Moreover, while the tunnel seems to spare the wetland, there is no guarantee it will not affect the area's water table. Should that happen, the wetland could turn dry and make farming impossible, defeating the objective of pursuing the expensive tunnel option. In fact, as some legislators pointed out last week, since Long Valley is in private hands, it could easily be drained dry and turned into a parking lot for container trucks, as has so often happened to private farmland in the New Territories. That would make Long Valley a very expensive parking lot. Rather than spending a fortune to build the tunnel, environmentalists say the Kowloon-Canton Railway Corporation should fine-tune its viaduct option to minimise disturbance to Long Valley. The money saved should then be used to buy up Long Valley and other ecologically sensitive areas so they could be preserved forever. The KCRC and the Government had opted for the tunnel option believing it would offer political certainty so there would be no further delays to construction. But that certainty has failed to materialise. The green groups might have performed a back flip, but their revised proposal for a viaduct deserves to be considered on its merits.