The New Zealand Transport Agency will be working on the bridges again today to complete the work.
The most debris is at the Hakataramea end of the northern bridge, and it is putting pressure on the piers and posing the danger of more scouring.
The bridge was closed last Saturday while a start was made to remove trees and other debris piled against the piers. However, the digger did not have a long enough reach.
Yesterday, the New Zealand Transport Agency brought in a logging machine with an arm long enough to reach into the piles of debris and grab them.
Abseiling tree fellers wearing wetsuits from OT's Tree Services in Timaru worked on cutting up the trees.
The problem was the trees stuck against the piers, which came downstream during flooding in January and last month, came down branches, rather than stump, first.
Flows of up to 1552cumecs jammed the trees under the bridge, wedging them in tightly. That meant yesterday some had to be cut free.
Those flows also closed the bridge to all traffic except pedestrians and cyclists from February 8 to 17.
Yesterday, with the river at 420cumecs (compared with its normal average of 350cumecs), progress was slow because of the way trees had jammed themselves in, particularly against the two piers.
The north bridge was closed to allow trucks and the logger to work over the side, but opened for five minutes on the hour and half-hour to let traffic through.
The agency's area manager, Colin Hey, said moving the debris was challenging and slower than expected.
The co-operation of Meridian Energy Ltd and Environment Canterbury in keeping flows down had made a big difference. That would continue today.
However, heavy rain in the upper catchment meant the river's level was expected to rise later today, which may hamper efforts to complete the work.
The twin bridges are due to be replaced by two-lane concrete structures by 2014, but still need resource consents and funding approval.
