Henry David Thoreau was more than an advocate of simple living and civil disobedience. He was also a naturalist who understood that nature was interconnected. He tried to understand how with his Yankee eye for practical detail. Thoreau anticipated the methods of environmentalism long before environmentalism was a word.
After a thunderstorm in his hometown of Concord, Mass., Thoreau turned his attention to the impact of summer freshets on the New England landscape. Did they help preserve open meadows? he wondered. And why are willows found on the banks of rivers but not in marshy meadows?
Thoreau wasn't a wilderness nut. Instead, he sought a middle ground for nature and human civilization. Walden Pond, after all, was near a thickly settled town. Irish laborers worked on the railroad nearby, and in the winter ice cutters who fell into the pond warmed themselves by his stove.
The farmers commonly say that the spring floods, being of cold water, do not injure the grass like later ones when the water is warm, but I suspect it is not so much owing to the warmth of the water as to the age and condition of the grass and whatever else is exposed to them. They say that if you let the water rise and stand some time over the roots of trees in warm weather it will kill them. This, then, may be the value of these occasional freshets in August: they steam and kill the shrubs and trees which had crept into the river meadows, and so keep them open perpetually, which, perchance, the spring floods alone might not do. It is commonly supposed that our river meadows were much drier than now originally, or when the town was settled. They were probably drier before the dam was built at Billerica, but if they were much or at all drier than now originally, I ask what prevented their being converted into maple swamps? Maples, alders, birches, etc., are creeping into them quite fast on many sides at present. If they had been so dry as is supposed they would not have been open meadows. It seems to be true that high water in mid-summer, when perchance the trees and shrubs are in a more tender state, kills them. It "steams" them, as it does the grass; and maybe the river thus assets its rights, and possibly it would still to great extent, though the meadows should be considerably raised. Yet, I ask, why do maples, alders, etc., at present border the stream, though they do not spring up to any extent in the open meadow? Is it because the immediate bank is commonly more firm as well as higher (their seeds also are more liable to be caught there), and where it is low they are protected by willows and button-bushes, which can bear the flood? Not even willows and button-bushes prevail in the Great Meadows,--though many of the former, at least, spring up there,--except on the most elevated parts or hummocks. The reason for this cannot be solely in the fact that the water stands over them there a part of the year, because they are still more exposed to the water in many places on the shore of the river where yet they thrive. Is it then owing to the soft character of the ground in the meadow and the ice tearing up the meadow so extensively? On the immediate bank of the river that kind of sod and soil is not commonly formed which the ice lifts up. Why is the black willow so strictly confined to the bank of the river? What is the use, in Nature's economy, of these occasional floods in August? Is it not partly to preserve the meadows open?
I was suggesting yesterday, as I have often before, that the town should provide a stone monument to be placed in the river, so as to be surrounded by water at its lowest stage, and a dozen feet high, so as to rise above it at its highest stage; on this feet and inches to be permanently marked; and it be made some one's duty to record each high or low stage of the water. Now, when we have a remarkable freshet, we cannot tell surely whether it is higher than the one thirty or sixty years ago or not. It would be not merely interesting, but often practically valuable to know this. Reuben Rice was telling me to-night that the great freshet of two or three years ago came, according to his brother Israel, within two inches of one that occurred about forty years ago. I asked how he knew. He said that the former one took place early (February?), and the surface froze so that boys skated on it, and the ice marked a particular apple tree, girdled it, so that it is seen to this day. But we wish to speak more confidently than this allows. It is important when building a causeway, or a bridge, or a house even, in some situations, to know exactly how high the river has ever risen. It would need to be a very large stone or pile of stones, which the ice could not move or break. Perhaps one corner of a bridge abutment would do.
With thanks to The Journal of Henry David Thoreau, 1837-1861.