ban
and suburban ugliness. The translation of rural techniques to city use
cannot be literal, for both urban hydrology and urban land use are
distinctive, and a good deal remains to be learned about making the
techniques work better there. But their basic principles are obviously a
main hope.

Other modifications of them, if put into wide practice, can cut down on
the heavy production of silt by strip mines in the upper Basin;
these involve both the reclamation of abandoned mines and the use
of more care in scraping new ones. And application of the same
principles--protective cover and detention of runoff--to new highway and
road construction, as well as to the reclamation of banks and shoulders
on old secondary roads, has to be achieved.

The silt already in the upper estuary, and likely to continue to be
deposited there even after the best available controls may have been put
into operation above, will need radical treatment. The tens of millions
of tons already choking the metropolitan river, the stockpile of
centuries, will have to be dredged out if the river is going to be as
pleasant and useful at the capital as it ought to be, and so will the
yearly additions that can inevitably be expected. This can be done if
the money is available, though a considerable unsolved problem, under
research at present, is where to put the silt after it has been taken
out of the river, for appropriate fill sites are growing scarce.

Turbidity in the sluggish upper estuary will continue to be a problem
too, for the fine particles of silt that cause it are the least affected
by standard land treatment and sediment control measures.
Polyelectrolytes--chemicals which when applied in quite small amounts
can coagulate such suspended silt and settle it out--offer some promise
as tools against turbidity and are being tried out experimentally above
one of the reservoirs on upper Rock Creek, with good results thus far.
Very possibly they may prove to be useful for clearing up the estuary
after it has been roiled by storm runoff, and for achieving some
control of murky waters around sand and gravel dredging operations.
However, ironically, it has also been pointed out that until the excess
of nutrients in the upper estuary is eliminated, such clearing of the
water could very possibly cause a great increase in the already
disastrous algae blooms, by allowing sunlight to penetrate to greater
depths and foster more production of this undelight