FLOOD02900

• County: Adams
• Community: Commerce City
• Basin: South Platte
• Title: Lower First Creek and Direct Flow Area 0055 Major Drainageway Planning
• Date: 5/1/2002
• Prepared For: UDFDC
• Prepared By: Turner Collie & Braden Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

ES-6

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The first improvement made in the watershed should be the construction of the Maul
Reservoir. TC&B evaluated the possibility of constructing the Maul Reservoir in multiple phases.
Based on that evaluation, it is recommended that the reservoir be developed in one phase due to the
limited cost-benefit of constructing the dam in multiple phases. Constructing the reservoir early will
allow for reduction of peak flows encountered downstream during large storm events. This is
particularly important due to the inability of the existing downstream structures to safely convey the
flows generated by the larger storm events. Prior to completion ofthe downstream improvements, it
is suggested that the Maul Reservoir outlet structure be fitted with gates to control more frequent
events (i.e. 2-, 5-, and to-year events) in the interim.

- The next priority would be to implement the charmel improvements along the main channel
of First Creek to convey the detained flows from the Maul Reservoir. This phase of improvements
would alleviate existing problems created by the lack of conveyance provided by existing drainage
facilities along First Creek.

Finally, the improvements to the channels in the Direct Flow Area 0055 should be
constructed to convey the flows from the tributaries in this area to the improved First Creek channel.
Construction of these improvements prior to completing improvements downstream along First
Creek could result in increased flood risks downstream. With the First Creek improvements in
place, the First Creek channel and drainage structures will have the capacity to handle the larger
flow rates caused by the increased conveyance of flow from the Direct Flow Area