news from the waterfront by Tim Matson
THE PONDKEEPER’S SEASONS: SPRING
"Ponds need no such labor and charges as other commodities do.” That was how the elder Pliny saw the needs for pond maintenance nineteen centuries ago, and it’s a view that still looks good -- especially for the cunning pond keeper who works with the seasons, synchronizing chores with the life cycle of the pond, and tapping the forces of nature for support.
The main spring maintenance objective is to be a good midwife at the rebirth of the pond after its long dark winter. The pond wants to take in big gulps of fresh, richly aerated water and flush out last year’s crud. You help. But beware: simultaneously the pond must be shielded against two threats that arrive with spring waters: erosion and silt.
The erosive, silting power of spring flood water is formidible. A stream that doubles its speed quadruples its load-carrying capacity. The more silt it carries, the greater the ability to erode. A vicious hydrologic cycle.
Moreover, at the same time that thawing snow and falling rain are adding to spring floodwaters, the shoreland heaves as frost works its way out of the ground. Spillways, ditches, and berms are undermined. Piping cracks and trash racks clog. In a few weeks of spring the pond is likely to suffer more damage than all the rest of the year.
As usual, good siting and construction make the best defense against reservoir wear and tear. In spring wise pond keepers will congratulate themselves for steering clear of big stream inflows;
even a small intermittent vein can deliver an avalanche of silt.
Throughout spring, water channels leading into and out of the pond should be cleaned and reinforced.
Debris in the vein feeding the pond will decay, eating up oxygen and tipping up water temperatures;
Debris in the spillway will back up overflowing water, causing erosion around the spillway approach channel and shore, not to mention the chance for flooding. Spring is also time to check for ice damage to piping.
Mind the watershed above the pond, especially cultivated farmland or terrain doused with manure, chemicals, or garbage. Open upstream land will feed detrius into ponds. Diversion ditches and berms around the upstream hemisphere of the pond help detour silt, but don’t dig them in spring! Refrain, too, early in the year, from logging, roadwork, or construction in the near upstream watershed.
Pipes that feed stream water to bypass ponds often clog in spring. A “Digger Dam” in the stream just above the intake pool will usually sweep silt around the pipe, and in conjunction with a screen and/or trash rack, will keep the inflow clear. For clearest passage through rough spring waters, some pond keepers find it simplest to close off side pipes at the source.
In spring I use an old logger’s trick for clearing roughed-up streams. I lay a hay bale crossways in the channel to filter out silt. Later, when the water warms up, I shovel out a wheelbarrow or two of spring silt, fine fill for the puddles that may have settled in the dam after construction.
(There are many new products available for filtering water and holding soil in place.) The marsh marigolds that I planted in the inflow channel help hold the streambed in place, too.
Stones cleared from the embankment after excavation become a thrifty resource, piled near the spillway for springtime repairs. This riprap can be paved in the inflow channel and along patches of muddy shoreline. Incidentally, rock paving is recommended both as an antidote for banks that erode under wind-whipped waves and as a barrier against fish poachers and pond unpluggers like otters and mink.
To finish off the rites of spring, I suggest you look at that off-color tint that sometimes appears on ponds thawing downwind of industrial smokestacks.
All winter, the ice and surrounding watershed has been catching polluted snow and rain. When it melts, six months of accumulated airborne rubbish sinks into the pond. There may be polluted runoff from neighboring land as well. It’s a bad time to stock fish. Better to wait a few weeks and let the pond flush.
From Earth Ponds: The Country Pond Maker’s Guide
To Building, Maintenance, and Restoration.
March 15, 2010