FLOOD08833

• County: Las Animas
• Community: Near Trinidad
• Stream Name: Purgatoire
• Basin: Arkansas
• Title: Flood Control Problem Purgatoire near Trinidad
• Date: 1/1/1944
• Floodplain - Doc Type: Project

PURGA1'OIRE (PICKET WIRE) RIVER, COLO.

33

96. Flood channel delineation.-The recommended plan of improve-
ment is !lescribed in paragraph 78. With this type of improvement
there is little likelihood of any encroachments by future rosidential,
commercial, or industrial construction that would In .,ny way constrict
the flood channel. In the event that the Ohestnut Street Bridge is
replaccd; thc structure should be located so that the center line of the
structure will be approximately on the center line of any future chan"
nel developments.m that particular reach. The !llear span should. be
adcquate to prOVide for the probable channel Widths, and any piers
in the channel should not give a ratio of channel constriction greater
than that of the Oolorado & Southern Railway Bridge, just, down-
stream from Ohestnut Street. Any future channel improvements
within the city of Trinidad should be in conformity with the recom-
mended plan of improvement in order to preserve its integrity,
97. Discu88ion.-Dissimilar type storms in the Purgatoire River
drainage area result in flood waves of comparable peak discharge, but
vary greatly in volume of run-off. The maximum flood of record in
the area under consideration occurred in September 1904, and a
flood of this magnitude would have a probable occurrence of about
once in 100 years. , .
98. In the area under consideration from Sopris Dam site (mile
163.3) ,to. the head of the .canyon section (mile 122), 5,000 acres.are
in the probable overflow area. Of this area, 370 acres are in the urban
area of Trinidag, 1,050 acres are cultivated, 400 acres are irrigated
pllstUl'e, 730 acres are grazinlj land and the remainder is waste, The
urban area of Trinidad con tams railroad tracks and yards, residences;
city parks, business and industrial establishments, highway and rail-
road bridges, streets, sewers, water and glls mllins, wire lines, and
other improvements of an urban nature. Both railroad and city
properl,y in the urban area are particularly susceptible to damage. In
the agricultural flood plain, cultivated acreage and fences sustain the
major flood damages to lands Ilnd improvements. Seven low eon-
crete aud several brush and rock diversion dams, headgate structures,
and canals are' partially or wholly destroyed' during floods. The
direct and indirect damages for the flood of April 1942, which affords
the most logical basis for reducing past flood damages to present eon"
ditions, were $530,200.
99. Local interests' plan for four regulatory reservoirs and one ir-
rigation storage'reservoir would benefit the val!ey by conservation ,of
floodwaters.' The sm'll!' Toseryoir storage capacity 'of these struc-
tures would not provide dependable flood control for the drainage
areas above the dam sites. The total benefits which would Mcrue
from ,the execution of the plan would not be great enough to warrant
the construction of the five reservoirs suggested by local 'interests. '
100. 'I'he construction of the John Martin Dam and Reservoir
{authorized by the Flood Oontrol Act of 1936, llS amended by the
Flood Oontrol Act of 1938) is now under way at a site on Arkansas
River, immediatel;r below the mouth of Purgatoire River, and will
provide a reservOir of sufficient capacity to control completely all
stream flows at its site, consequentl,}', there is no immediate need for
reservoirs in the lower Purgatoire River BllSin to provide supplemen-
tary water supply in ArkansllS River. The "308" studies have indi-
cated, and the present studies confirm, that the benefits to be gained in
the lower Purgatoire River BllSin from the development of supplemen,