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<br />4.3
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<br />Field Survevs and Cross-Section Prevaration
<br />
<br />Since most of the scudy reach on the Colorado River mainstem had already been studied by
<br />dctalledmethods, and since the unstudied portions of the sIUdy reachfeJl into the "Narrow" or
<br />"Canyon" categories, only one cross-section was actually field-surveyed. The selection of the
<br />field-surveyed cross-section was based on the location of a series offish ponds at the Islalld
<br />Acres State Park where the Colorado Division of Wildlife had an inlerest in some specific
<br />floodplain information. The availability of a benchmark, easy access and the ability to survey
<br />the opposite bank dictated the specific location within the State Park. A field estimate was made
<br />of the average water depth. but the channel bottom was not surveyed. Estimates of the
<br />Mannings'n'valuesweremadeatthesurveyedcross-sectionlocationduringthefleldsurvcy.
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<br />Map-derived cross-sections were utilized for the remaining unstudied reaches, No adjusUllents
<br />were made to those cross-sections prior to performing the depth computations. Canyon reaches
<br />on the Colorado River mainstem generally were not represented by cross-sections since the level
<br />of detail obtained could not be shown on the base maps. One exception is noted below.
<br />
<br />GARFIEW CO.
<br />
<br />
<br />Since the majority of the study reach consisted of existing detailed infonnation or canyons (64
<br />of the 93 miles are detailed, 24.5 miles are in canyons), only three cross-seclions were used in
<br />the hydraulic analysis. Two types of cross-sections were used in the unstudied reaches of the
<br />Colorado River mainstem:
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<br />Type 1
<br />Type 2
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<br />Field-surveyed cross-sections used only in the representative reach:
<br />Map-derivedcross-~ections used only in tlrerepresentalive reach.
<br />
<br />By using these categories to identifY cross-section sources, 3 of the 12 reaches on the Colorado
<br />River mainstem were divided into the following groups:
<br />
<br />Type 1 Cross-section.
<br />Type 2 Cross-sections-
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<br />I reach
<br />2 reaches
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<br />One of the map-derived cross-sections (fype 2) was used for a canyon reach, Although thaI
<br />cross-section is included in this report, the fl{)l)l.\plainddineationwas notsignifi cantlydifferenl
<br />thanitwouldhavebeensirnplyfollowingthecanyonwalltopography,aswasdoneintheother
<br />3 canyon reaches,
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<br />There were 9 additional reaches which were classified as follows: 3 canyon reaches for which
<br />no cross-sections were developed (this excludes thc 4th canyon reach iorwhich a map-derived
<br />cross-scclion was used): 6 reaches where detailed studies had already bel:nperfonned.
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<br />TableS identifies the cross-sections, the group type and flow values used to calculate the flood
<br />depths. The cross-sections, with SO-)'car and l00-year flood lines illustrated. are presented after
<br />Section 4.4 in Figures 7A-7C.
<br />
<br />FIGURE 6
<br />LOCATION OF SlUDY RI;!ICHES
<br />B~,in lIounda'1'
<br />County Un. Slud)'R",,~h I
<br />. Cil~
<br />SCAL1;: Ono inch "'luals apprnximatol)' Il>lIIil",
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<br />COI-ORAI)() RIV};R BASIN
<br />COLORADO WATER CONSERVATION BOARD 31'15
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