FLOOD09312

• Designation Number: 370
• County: Crowley
• Community: Ordway
• Stream Name: Local Drainage
• Basin: Arkansas
• Title: Floodplain Study and Master Drainage Plan - Ordway, Colorado
• Date: 6/1/1987
• Designation Date: 7/1/1994
• Floodplain - Doc Type: Floodplain Report/Masterplan

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6

and have poor internal drainage. Available water holding capacity is low in
the subsoil. Because the surface layer has slow permeability, runoff is
enhanced. Natural fertility is low to moderate, but these soils are subject
to soil blowing unless they are protected by growing crops or crop residue.
These soils are classified as a "0" soil type, as defined in the SCS
hydrologic methodology, runoff and curve number values range from CN 80 to 89.
The vegetative cover of the major drainage basins is classified as rangeland
in moderate to poar canditian. Irrigated land is alsa prevalent in the lawer
partians .of the majar drainage basins. These irrigated lands primarily con-
sist of row-type crops under goad irrigation and cultivation practices.
Figure 2 is a generalized map of the soils within the study area.

Land Use
Figure 3 presents the land uses used in the hydrolagic modeling. Land
uses were obtained from the most current Town .of Ordway Zoning Map. Several
variaus types of land uses were identified, including single-family residen-
tial, multi-family residential, cammercial, and industrial uses. Proposed
1 and develapment projects which were cansidered when evaluating the runaff
characteristics .of the area are summarized an Table 1.

Rainfall
Rainfall data lias .obtained from the "Precipitatian - Frequency Atlas .of
the Western United States, Valume III - Calorado", published by the National
Oceanic and Atmaspheric Admi nistration, in 1973. Peak discharges for the 5-,
10-, 50-, and 100-year flows under existing drainage basin canditians were
predicted using rainfall depth .of the 2- and 6-haur duratian starms specific
ta the Ordway area. Rainfall/depth distributians are summarized in Table 2.
The duratian .of a starm reflects the type .of starm and is significant
depending an the size .of the drainage basin. The shart duratian starm pat-
terns of 6 hours and less typically cause floods in smaller drainage basins,
generally 10 square miles and below. An example .of a short duration storm is
a highly lacal ized cloud burst event, which causes floading because of the
almost instantaneaus runaff. Longer duratian storms, 6 hours and greater, are