[Code of Federal Regulations]
[Title 33, Volume 3]
[Revised as of July 1, 2001]
From the U.S. Government Printing Office via GPO Access
[CITE: 33CFR220.1]

[Page 192-193]
 
                TITLE 33--NAVIGATION AND NAVIGABLE WATERS
 
         CHAPTER II--CORPS OF ENGINEERS, DEPARTMENT OF THE ARMY
 
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 193]]

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]