Study Classification

Hydrologic engineers in USACE are called upon to provide information for decision making for:

  • Planning and designing new flood-damage reduction facilities. These planning studies are commonly undertaken in response to floods that damage property and threaten public safety. The studies seek solutions, both structural and nonstructural, that will reduce the damage and the threat. Hydrologic and hydraulic information forms the basis for design and provides an index for evaluation of candidate damage-reduction plans.
  • Operating and/or evaluating existing hydraulic-conveyance and water-control facilities. USACE has responsibility for operation of hundreds of reservoirs nationwide for flood control, water supply, hydropower generation, navigation, and fish and wildlife protection. Watershed runoff forecasts provide the information for release decision making at these reservoirs.
  • Preparing for and responding to floods. Beyond controlling flood waters to reduce damage and protect the public, USACE activities include flood emergency preparedness planning and emergency response. In the first case, a thorough evaluation of flood depths, velocities, and timing is necessary, so that evacuation routes can be identified, temporary housing locations can be found, and other plans can be made. In the second case, forecasts of stage a few hours or a few days in advance are necessary so that the response plans can be implemented properly.
  • Regulating floodplain activities. As part of USACE's goal to promote wise use of the nation's floodplains, hydrologic engineers commonly delineate these floodplains to provide information for use regulation. This delineation requires information about watershed runoff, creek and stream stages, and velocities.
  • Restoring or enhancing the environment. The USACE environmental mission includes ecosystem restoration, environmental stewardship, and radioactive site cleanup. Each of these activities requires information about the hydrology and hydraulics of sensitive sites so that well-informed decisions can be made.

In addition, since passage of the Rivers & Harbors Act of 1899 USACE has been involved in regulating activities in navigable waterways through the granting of permits. Information about flow depths, velocities, and the temporal distribution of water is vital to the decision making for this permitting.

Study Process Overview

For any of the studies listed above, one of the initial steps is to develop a "blue print" of the study process. EP 1110-2-9 (USACE, 1994b) describes the steps needed in a detailed Hydrologic Engineering Management Plan (HEMP) prior to study initiation. A HEMP defines the hydrologic and hydraulic information required to evaluate the National Economic Development (NED) contribution and to ascertain satisfaction of the environmental-protection and performance standards. It also defines the methods to be used to provide the information, and identifies the institutions responsible for developing and/or employing the methods. From this detailed technical study plan, the time and cost estimates, which are included in the HEMP, can be developed. The HEMP maximizes the likelihood that the study is well planned, provides the information required for proper decision making, and is completed on time and within budget.

The USACE approach to flood studies is to follow a process that involves planning, design, construction, and operation. The sequential phases are described in in the table below. The initial HEMP is prepared at the end of the reconnaissance phase; this defines procedures and estimates resources required for the feasibility phase. At the end of the feasibility phase, a HEMP is prepared to define procedures and estimate resources for the design phase. At the beginning of the feasibility and design phases, a HEMP may also be prepared to define in detail the technical analyses.

Description of Project Phases

Project Phases

Description

Reconnaissance

This is this first phase. In this phase, alternative plans are formulated and evaluated in a preliminary manner. The goal is to determine if at least one plan exists that has positive net benefit, is likely to satisfy the environmental-protection and performance standards, and is acceptable to local interests. In this phase, the goal is to perform detailed hydrologic engineering and flood damage analyses for the existing without-project condition if possible. If a solution can be identified, and if a local sponsor is willing to share the cost, the search for the recommended plan continues to the second phase.

Feasibility

In this second phase, the set of feasible alternatives is refined and the search narrowed. The plans are nominated with specific locations and sizes of measures and operating policies. Detailed hydrologic and hydraulic studies for all conditions are completed as necessary "... to establish channel capacities, structure configurations, levels of protection, interior flood-control requirements, residual or induced flooding, etc." (ER 1110-2-1150 - USACE, 1999). Then, the economic objective function is evaluated, and satisfaction of the performance and environmental standards tested. Feasible solutions are retained, inferior solutions are abandoned, and the cycle continues. The NED and locally preferred plans are identified from the final array. The process concludes with a recommended plan for design and implementation.

Design

In this phase (also known as the preconstruction engineering and design (PED) stage), necessary design documents, plans, and specifications for implementation of the proposed plan are prepared. These further refine the solution to the point that construction can begin. Engineering during construction permits further refinement of the proposed plan and allows for design of those elements of the plan not initially implemented or constructed. Likewise, the engineering during operations stage permits fine-tuning of operation, maintenance, replacement, and repair decisions.

The contents of a HEMP vary slightly depending on the study phase, but all contain the best estimate of the work to be performed, the methods for doing so, and the associated resources required.