MILFORD, N.H. (AP) – Heavy rain and melting snow rather than water released from dams caused last April’s severe flooding along the Souhegan River, according to preliminary results of a state study.

Gov. John Lynch ordered a review of how dams are managed after some residents of Milford, Amherst and Merrimack said a surge of water pushed the river to unprecedented levels. They questioned the role of three hydropower dams in Greenville and Wilton, but the state said the dams were not to blame.

“The dams in the Souhegan River watershed which were suspected as contributing to the flooding, likely had gates open prior to the flood or early in the event, and were not likely to have been important factors,” wrote James Gallagher, chief engineer for the New Hampshire Department of Environmental Services, in a Jan. 7 letter to Milford Rep. Peter Leishman. Instead, the flooding was caused by 4 inches of rain that fell in 12 hours.

The amount of rain was far from record-setting, but such large amounts are more common later in the year, after snow already has melted and the thawed ground can absorb the moisture. Last April, a sudden rise in temperature accompanied the rain, quickly melting the snow, which washed over the frozen ground into the river.

Among the resulting problems was the bursting of a private earthen dam in south Milford and a stone dam in Hollis that officials broke open because of concern that it would give way.

Gallagher’s letter said more answers may come next month, when officials release the full study of flooding on 10 rivers in southern New Hampshire.

According to his letter, the owner of the two Greenville dams manually removed several of the flashboards on April 15, the day before the flooding. That conflicts with reports given to some area fire chiefs, who were told that the Greenville dams were to have their flashboards removed Monday.

In Wilton, where the dam flashboards cannot be manually removed, the boards may have given way on the morning of April 16, possibly corresponding to the rise in river levels that left an apartment complex flooded. But Gallagher said the holding area behind that dam is relatively small. Altogether, the total amount of water held back by the three dams is 5 million cubic feet, or less than .3 percent of the more than 1.7 billion cubic feet of water that flowed past a U.S. Geological Survey river gage in Merrimack during the flood.

“Some of the conflicting information regarding dam operations will be reconciled as part of the independent evaluation of the flood,” the letter said.


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