31 Mar 95
when the Napa River is below flood stage. A major HEC goal
Federal (USGS, SCS, USBR, etc.).
is to provide the district with the capability of applying HEC's
Interior Flood Hydrology (HEC-IFH) program. The degree to
which HEC is involved in the formulation process is negotiable.
The district will provide stage-damage relationships and other
data required to perform the expected annual damage
computations for each plan. Cost estimates of the flood damage
reduction measures and plans are also to be provided by the
district. The district will be responsible for those tasks
Scope major hydrologic engineering analysis activities.
described in Sections C-1-2, C-1-3, and C-1-4, including
preliminary investigations, data development and assembly, and
Prepare Hydrologic Engineering Management Plan.
evaluation of without-project conditions for the Napa River.
Obtain study area maps.
Some of the tasks described in this plan are required for the
general hydrologic engineering investigations for the levee,
floodwall, and channel improvement features of the Napa River
County highway maps.
Project. Accordingly, several of the tasks may have already
been accomplished. Design requirements for conveyance
systems, inlet and outlet works, and cost estimates for project
components are not included in the Hydrologic Engineering
Existing storm sewer design and configuration. The
existing and any proposed storm sewer layout, discharge design
C-1-2. Preliminary Investigations
capacities, and elevation of the inverts of the conveyance
network are important for defining drainage areas, minimum
This initial phase includes conducting a literature review of
facilities, and invert elevations of major conveyance to outlets,
previous reports, obtaining the available data, and requesting
gravity outlet inverts, pumping station on-off elevations, and
additional information needed to perform the investigation.
design criteria for inlet and outlet works.
(1) Determine layout and design of existing systems
(usually obtained from local public works department or City
(1) Confer with other disciplines involved in the study to
determine the objectives, the hydrologic engineering information
requirements of the study for other disciplines, study constraints,
(2) Determine layout and design of potential future
systems. Local drainage system enhancements that have been
planned and designed by local interests should be
Discuss study type, scope, and objectives.
Review available documents.
(3) Determine location of flow concentration at the line-of-
protection where gravity outlets or pumps may be located and
the layout of collector/conveyance systems adjacent to line-of-
protection to concentrate flows at these locations where
Previous Corps work.
d. Estimate location of cross sections on maps.
(Floodplain contractions, expansions, bridges, etc). Determine
mapping requirements (orthophoto) in conjunction with other
(4) Obtain historic and design discharges, discharge-
frequency relationships, high-water marks, bridge designs, cross
(1) Napa River from downstream of the project through
sections, and other data.
the upper end of project.
(2) Major ditches, channels, in the interior areas that will
convey flood waters to the interior area outlets.