[Code of Federal Regulations]

[Title 33, Volume 3]

[Revised as of July 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 33CFR220.1]



[Page 201-202]

 

                TITLE 33--NAVIGATION AND NAVIGABLE WATERS

 

 CHAPTER II--CORPS OF ENGINEERS, DEPARTMENT OF THE ARMY, DEPARTMENT OF 

                                 DEFENSE

 

PART 220_DESIGN CRITERIA FOR DAM AND LAKE PROJECTS--Table of Contents

 

Sec.  220.1  Low level discharge facilities for drawdown of impoundments.











    (a) Purpose. This regulation states the policy, objectives, and 

procedures in regard to facilities for drawdown of lakes to be impounded 

by Civil Works projects.

    (b) Applicability. This regulation is applicable to all Divisions 

and Districts having responsibility for design of Civil Works projects.

    (c) Policy. It is the policy of the Chief of Engineers that all 

future lakes impounded by Civil Works projects be provided with low 

level discharge facilities to meet the criteria for drawdown set forth 

in this ER. Low level discharge facilities, capable of essentially 

emptying the lake, provide flexibility in future project operation for 

unanticipated needs, such as, major repair of the structure, 

environmental controls or changes in reservoir regulation. The criteria 

set forth in this ER will govern in the majority of impoundment 

projects. However, it may be impracticable to provide the drawdown 

capability to meet the criteria for certain projects because of their 

size (unusually small or large) or because of their unique function. 

Such projects may be exempt from the criteria upon presentation of 

information in accordance with paragraph (e) of this section.

    (d) Design criteria. As a minimum, low level discharge facilities 

will be sized to reduce the pool, within a period of four months, to the 

higher of the following pool levels: (1) A pool level that is within 20 

feet of the pre-project ``full channel'' elevation, or (2) a pool level 

which will result in an amount of storage in the reservoir that is 10 

percent of that at the beginning pool level. The beginning pool level 

for drawdown will be assigned at spillway crest for uncontrolled 

spillways and at top of spillway gates for controlled spillways. Inflow 

into the lake during the drawdown period will be developed by obtaining 

the average flow for each month of the year. The drawdown period inflow 

will then be assumed equivalent to the average flow of the highest 

consecutive four-month period.

    (e) Design Study and Report Requirements. Feasibility (survey) 

reports and subsequent pertinent design memoranda should include the 

results of studies made to determine facilities required for drawdown of 

impoundments. The discharge capacity required to satisfy project 

purposes and diversion requirements during construction may be 

sufficient to meet the drawdown criteria set forth in paragraph (d) of 

this section. Where additional capacity is required, studies will be 

made to determine the most practical and economical means of increasing 

the capacity to meet the drawdown criteria. A synopsis of the 

alternatives considered and details of the recommended plan should be 

included in the Phase II General Design Memorandum or a feature design 

memorandum. The reporting should include the effects of the required 

discharge capacity on project costs, on existing downstream projects, 

and on the potential for downstream damage. When, due to specific 

project conditions, a drawdown capacity is recommended which does not 

meet the criteria set forth in paragraph (d) of this section, the 

following information should be presented:

    (1) The drawdown period using the maximum drawdown capability of the 

proposed project facilities, under the situation described in paragraph 

(d) of this section. Information should be included on the pool 

elevation and corresponding storage volume at end of the period.

    (2) Information on facilities that would be required to meet the 

design criteria for drawdown, including the estimated first cost and 

annual cost of these facilities. If the estimated cost for such 

facilities is significantly greater than for the proposed project 

facilities, similar information on intermediate facilities should be 

provided.



Reporting subsequent to the Phase I General Design Memorandum should 

include related discharge rating curves; hydrographs with inflow, 

outflow and pool stage plots; lake regulation plans needed for project 

purposes and needed to satisfy the drawdown criteria; and



[[Page 202]]



other data essential in evaluating the study.



(49 Stat. 1571, 33 U.S.C. 701c)



[40 FR 20081, May 8, 1975, as amended at 40 FR 36774, Aug. 22, 1975]