ETL 1110-2-367
31 Mar 95
Appendix C
minimum facilities for the interior areas. The limited rainfall
and stream gauge records for the study area also present
Hydrologic Engineering Management
problems. The district is to provide significant guidance, and
Plans for Analysis of Interior Flood
where possible, data to address these issues. HEC has retained
Damage Reduction Measures, Napa,
(under contract) the recently retired city engineer of the City of
California
Napa to assist with specific aspects of the existing flow patterns
and storm sewer system.
d. Hydrologic engineering analysis of the interior areas is
C-1.
Background
to be performed using the HEC-Interior Flood Hydrology (HEC-
a. The Hydrologic Engineering Center (HEC) is
IFH) program (USACE 1992). HEC will establish the with-
and without-project conditions for the interior areas. Several
performing an interior flood hydrology study of the City of Napa,
size gravity outlets and pumping station capacities will be
CA, for the U.S. Army Engineer District, Sacramento. The
investigated.
district is considering a series of levees to reduce the flood
damage potential to the city caused by flooding of the Napa
e.
HEMP strategy and procedures were defined using an
River, which flows through the center of the town. Interior
annotated outline format. Study cost estimates are based on the
flooding that would result because of the levees must be
tasks and the assumption that a junior engineer will perform the
addressed as part of the plan. The study is a preconstruction
analyses under the direction of a senior engineer. Cost estimates
engineering and design reaffirmation study.
include actual engineers' salaries times a factor of 2.8 to account
b. The initial task was for HEC to develop a Hydrologic
for overhead. Overhead charges include secretarial and
reproduction expenses. The total HEC cost to perform the study
Engineering Management Plan (HEMP) to be used in
is ,000. This is based on the district providing HEC a
performing an interior flood hydrologic engineering analysis for
substantial amount of precipitation, runoff, exterior stage, and
the study area. The plan, or HEC's proposal, was to be the basis
storm sewer alignment data. The cost is estimated to be more
for deciding if HEC would proceed with the technical study.
than 0,000 if performed entirely by HEC. A Gant style
The district funded HEC ,000 to develop the HEMP. The
schedule was subsequently developed based on study milestones
final HEMP that was agreed upon is attached as Exhibit C-1.
defined by the district and the major study tasks to be performed.
C-2.
Hydrologic Engineering Management Plan
Development
Exhibit C-1
a. The development of the HEMP for the Napa study was
C-1-1. Introduction
based on several discussions and reviews. These included
a. This Hydrologic Engineering Management Plan
discussions with the district's technical and project management
staff, review of available information including that from
(HEMP) is developed for the Sacramento District to be used in
previous studies, review of engineer manuals and other guidance
hydrologic engineering analysis of interior flood damage
(USACE 1988a, 1990, and 1992), and a field reconnaissance of
reduction measures for the City of Napa, CA. Objectives of the
the study area.
hydrologic engineering analysis are to determine (a) the
minimum outlet facility associated with the line-of-protection,
b. The study and project managers, engineers, and
(b) existing and future stage-frequency relationships for without-
economists made presentations and met with the HEC staff to
project conditions, (c) stage-frequency relationships for a range
review the Napa study. Two subsequent meetings between
of gravity outlet and pumping station sizes and configurations
HEC and the district's hydraulics staff were held to scope the
for the interior areas, and (d) a formulated set of viable flood
interior study and to determine the information the district would
damage reduction plans for each interior area (with the
provide. Maps and previous reports were provided to HEC. A
assistance of the district staff).
detailed field reconnaissance was conducted by HEC and a
b. The HEMP includes a proposed schedule, person-day,
meeting was held to review the study with a representative of the
Napa City Engineering staff.
and cost estimate for the hydrologic engineering tasks that HEC
would be responsible for completing. These tasks include those
c.
Key issues identified were the potential effect of San
described in Sections C-1-5, C-1-6, and C-1-7, "Minimum
Pablo Bay tidal fluctuations on the exterior stages of the lower
Facilities Analysis," "Formulation and Comparison of Interior
study area reaches, tieback levees and associated closure of
Flood Damage Reduction Measures," and "Technology
openings in the highly urban area of Napa Creek, definition of
Transfer." HEC will also be responsible for the portions of
the flow patterns for the interior areas, and analysis of the
Section C-1-4 which deal with the assessment of local flooding
C-1
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