FLOOD00959

• Designation Number: 143
• County: Denver
• Community: Denver
• Stream Name: Marston Lake North
• Title: Flood Hazard Area Delineation - Marston Lake North
• Date: 2/1/1979
• Designation Date: 3/18/1979
• Prepared For: Denver
• Prepared By: UDFCD
• Floodplain - Doc Type: Floodplain Report/Masterplan

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V. FLOODPLAIN AND FLOODWAY SUMMARY

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of drainageway. From this table it is estimated that approximately

460 cfs enters over the Marston Lake embankment.

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2-year 5-year lO-year
Location ....J.<:.fs)_ _-L'O!~ (ds)
Colorado State Highway 121 210 420 680
Marston Water Treatment Plant 230 440 620

50-year
(ds)

lOa-year
(ds)

Flood Hazards

The lOa-year flood event is considered by the State and the District as

the flood magnitude for which floodplains should be designated for

regulatory and improvement purposes. The lOa-year floodplain limits

and water surface profiles are shown on the Flood Hazard Area Delinea-

tion Maps at the back of this report.

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TABLE IV

Flood Discharge After Losses To Marston Lake

980 1040
660 680

The major flood hazard which is pointed out by this report is the po-

tential inflow of stormwaters to Marston Lake. Damage to filter sys-

tems in the Denver Water Board Marston treatment facility could occur,

causing shut-down of plant operations. Moreover, the water quality of

the reservoir could be indefinitely affected, causing possible future

water supply problems for the Denver Water Board.

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For reaches of drainageway downstream cross-section 128, full flows of

Table III are again resumed. These flow conditions represent the assump-

tion that the flow obstructions discussed above wash out and no flows are

lost to Martson Lake.

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Critical depth occurred in numerous locations along the entire channel.

The critical depth was assumed at those locations for water surface

profile computations.

Houses along Marston Lake are also affected by the stormwaters. Low-

lying areas to the north of the lake, in the vicinity of Marston Shores,

are flooded by the backwater due to the downstream constrictions and

adverse slopes occurring along the existing channel. Damage to struc-

tures and their contents are the major hazards associated with the 100-

year flood events.

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Floodplain and Floodway Data

The limits of future flooding are outlined on the Flood Hazard Area

Delineation maps and tabulated in Table V, Floodplain and Floodway

Reference Data. The tables list the potential flood discharge, flood

elevation, mean velocity, flooding widths and channel bottom elevation

at each cross-section along the entire study reach. The lOa-year and

la-year water surface profiles, channel thalweg profile and floodplain

limits at any point in the study reach are graphically shown on the

drawings 4 of 12 through 12 of 12.

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The floodway computations are based on passing the lOa-year flood with

an equal degree of encroachment which results in a total water surface

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