FLOOD09157

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Flood Hazard Mitigation Plan for Colorado
• Date: 1/1/1983
• Prepared For: State of Colorado
• Prepared By: CWCB
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

2.2.~ Causes of Floods

Floods in Colorado occur <m "riverine" systems consisting of
a basin (or watershed) and a hierarchial order of stream channels
which convey the normal flow of water through the watershed, The
area adjacent to the channel ill the floodplain. Flooding results
when the flow of water is greclter than the normal carrying capa-
city of the stream channel. The ra,te of rise, magnitude (or peak
discharge), duration and freqllency of floods are a function of
specific physiographic characteristics. GEmerally the rise in
water surface elevation is quite rapid on small (and steep
gradient) streams and slow in large (and flat sloped) streams.

The causes of floods relate directly to the accumulation of
water from precipitation or the fi!ilure of man-made structures
such as dams or levees,

Floods caused by precipitation are further classified as
coming from:

1. Rain in a general :,torm system
2, Rain in a 10cali~e<1 intense thunderstorm
3 . Mel t ing snow
4. Rain on melting sn<)\\,

Rainfall and melting snOw in the mountains feed four major
river systems with headwaters in Colorado as shown in figure
2.10. These are the Missouri, Arkansas, Rio Grande, and Colorado
River Basins, These basins encompass man.y small streams and
rivers as shown in figure 2.7.

Precipitation in each baBin i.s related to the seasons and
two major sources of moisture. Summer ShOWE!rS and thunderstorms
that occur from June through September primarily are caused by
moisture from the Gulf of Mexico or the Pacific Ocean. During
the fall, occasional general rainst:orms and thunderstorms occur
from wet and warm cyclonic air masses which move in from the
southern Pacific Ocean. winter and spring rain and snow storms
are generally a result of moist air masses which originate in the
cooler northern Pacific Ocean ,!nd move inland across the Pacific
Northwest.

of:

Floods caused by fail ure of man-made structures are a result

1. Hydrologic deficiencies
2. Structural deficiencies
3. Improper Operation or Sabotage

Each of these causes results i.n floods which
characteristics relative to rate of rise, volume,
flood season. Figure 2.11 is a comparison of
characteristics using flood hyclrographs,

have distinct
duration, and
typical flood

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