just as in water supply, ultimate "hard"
technology is undoubtedly going to make better solutions possible, while
a strong and meaningful start is possible with the technology that is on
hand.

* * * * *

Silt is a truly Basinwide problem. The individual tiny grains of soil
that mass to sully and choke the estuary may have originated anywhere
in the thousands of square miles of drainage above. They constitute an
economic loss at their points of origin as well as a trouble all along
their downstream course of migration.

The basic-physical ways of preventing silt are twofold and easily
defined: first, the maintenance of proper land cover--vegetation or
humus or mulch which blankets and anchors the soil particles and
prevents falling or flowing water from dislodging them--and second,
structural approaches that control the flow of water and can also serve
to trap eroded material. These latter can be anything from good contour
plowing practices to a major reservoir with a certain silt capacity
built into it.

[Illustration]

Such techniques are the basis of existing programs of the Soil
Conservation Service and the Forest Service that have proved their
effectiveness over many years of rural application. Watershed planning
with small reservoirs, check dams, and terraces backed up by good land
treatment and use, soil surveys, wise forestry practices, and such
things are stimulated and bolstered in these programs by technical and
financial assistance given to private landowners, States, and local
organizations. They have already had important local effects in the
Potomac States as throughout the country, but for maximum value in
relieving sedimentation they are going to need much wider and more
intensive application.

In modified form, they can be effective against newer and more
concentrated sources of silt, while sometimes accomplishing other
purposes as well. As we noted in discussing metropolitan pollution,
urban land undergoing development can enormously benefit from good
watershed planning. Preservation of critically erosive and flood-prone
land in grass and forest, insistence on prompt re-vegetation of bared
land and the use of such things as sediment detention basins by
developers, the construction of small headwater reservoirs when they are
needed to trap silt and reduce flooding--all these elements of watershed
planning are effective not only against silt but against standard ur