BOARD01914

• Board Meeting Date: 12/4/1974
• Description: Agenda or Table of Contents, Minutes, Resolution
• Board Meetings - Doc Type: Meeting

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the low hazard area; It'!. our aifiginal draft we had pt'OpOflCld that certain
uses could be made in the low hazard area. These are areas which we
consider almost a backwater area. There are areas on the fringe of
the floodplain in which the water simply collects because of the low
elevation and does not move or moves very slowly. This is what we
defined as a low hazard area. There are many ways to define it. We
defined it as an area in which the water would not either exceed a
depth of one foot or exceed a velocity of three feet per second. To
give you an idea of the three feet per second. one foot per second is
equivalent to seven-tenths of a mii.e per hour. So three feet per
second is equivalent to rate of movement a little over two miles per
hour. or this is about equivalent to the average walking pace of the
average person. Now this was contested. On one hand, there were many
people who felt that the hazard was too great to expose anyone to. On
the other hand. there were many who said that was too restrictive.

It is simply a matter of judgment and obviously we can't satisfy every-
one. This question was posed at a statewide meeting of.the counties
and cities and interested agencies held in Denver recently under the
auspices of the Urban Drainage and Flood Control District and this
board. We got a division of about fifty-fifty. That same division was
reflected in the letters we received. We made some slight changes in
that section. We divided the low hazard area into two categories. the
residential area and the nonresidential area. For the residential
area. we retained our criteria of depth not to exceed one foot and a
velocity not to exceed three feet. However. for flexibility we added
a numerical product stating that the velocity in miles per hour multi-
plied by depth could not exceed three. This means that you could have
a half foot depth and a greater velocity than three miles per hour.
But ih no case could the depth exceed one foot. The velocity could
exceed three feet per second if the depth were less than one foot.
That was the reason for the product of a velocity plus depth. Then in
the nonresidential area we increased the depth to not to exceed two
feet and a product of depth plus velocity not to exceed seven. This
allows considerably more flexibility in a nonresidential area. with the
limitation that the depth could not in any case exceed two feet and a
combined product of the depth plus velocity could not exceed seven.
Whether or not this will be acceptable to anyone or everyone. we don't
know. We think that the opinions ~ill still be pretty equally divided.
As far as our staff is concerned. we do not intend to go any further
in defining the low hazard area without some solid evidence that this
is in error.

We have made a comprehensive survey of the ordinances and laws of
virtually every state in the United States that has adopted floodplain
regulations. We have incorporated the best ideas that we could find.
We have read almost every publication in the field of floodplain des-
ignation and we have put together the best that we could find in all
the available information. Our approach is considerably different from
any other jurisdiction in the United States in that we set out to
define what could not be done in a floodplain zone rather than saying
what could be done. Most ordin~nces and regulations contain page after
page of things that can be done, like swimming. agriculture. horticulture.
and numerous other things. With that rather lengthy explanation.

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