FLOOD03313

• County: Denver
• Basin: South Platte
• Title: Drop Structures in the Denver Metropolitan Area
• Date: 12/1/1986
• Prepared For: UDFDC
• Prepared By: McLaughlin Water Engineers, Ltd.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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SECTION III
VERTICAL DROP WITH LOOSE RIP RAP BASIN

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INTRODUCTION

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Energy dissipation IS achieved In thIs type of drop by flow plunging Into a pool

where the energy IS expended by turbulence. The pool IS created by specific

placement and construction of a baSin, or by a "planned" rearranqement of rock by

the flow.

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The present UDFCD standards IS descrIbed In, DeSign Criteria for Rlprap Drop

Structures (ref. 63). The criteria was based upon a presentation by Stevens, Hydraulic

DeSign Criteria for Rlprapped Chutes and Vertical Drop Structures (ref. 58) which

was based upon phYSical model testing.

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The structural deSign for the vertICal crest wall IS complicated by the lack of

downstream support, seepage, soil saturation and hydraulic loading on the upstream

Side. In sandy or erosive sOils, It IS qUite common to use sheet pile for crest wall

construction, whIle caissons may prove acceptble for certain other appl1catIons.

Commonly a retaInIng wall IS used after evaluating seepage control.

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CASES

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There IS a Wide varIety of crest wall alternatives for vertical drops. The follOWing
cases Illustrate a number of eXisting appl1ctlDns.

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Case 29 - Little Dry Creek at Krameria, Arapahoe County

ThiS deSign is referred to as a check drop and is intended to control the hydraulic

grade line while leaving the invert slope at a natural Of steeper gradient. The

concept works best with deeper confined channels with steep side slopes, and utilizes

the downstream crest to cause backwater submergence of the upstream drop. In

some ways thiS IS SimIlar to the Corps' approach for "Derrck Stone" protection of

sheet pile drops whIch also requires crest submergence (ref. 13, 23, see diSCUSSion

In Section X).

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