Goals of Stream Restoration

According to Fischenich (2001), the conversion of forests, farmland, wood lots, wetlands, and pasture to residential areas and commercial and industrial developments directly impacts stream and riparian corridors by:

  • Altering stream channels through straightening, lining, or placement of culverts.
  • Reducing riparian corridor width through floodplain encroachments.
  • Increasing sediment yield during development and increasing pollutant loading following development.
  • Displacing native riparian plant communities by invasive non-natives.

Indirect impacts of this urbanization include:

  • Greater and more frequent peak storm flows, and longer duration of stream flows capable of altering channel beds and banks.
  • Enlargement of the channel through incision and widening processes.
  • Decreased recharge of shallow and medium-depth aquifers that sustain base and low flows.
  • Increased stream temperatures and higher nutrient and contaminant loading.
  • Alteration of the channel substrate.
  • Reduction of stream system function.
  • Reduction of riparian corridor function.
  • Reduction of native wildlife species.

Historical restoration concepts emphasized returning an ecosystem toward its condition before disturbance (NRC, 1992). Current Civil Works aquatic ecosystem restoration objectives address degraded structure and function, with measurable success indicators and a systems perspective (EP 1105-2-70 (USACE, 2025), paragraphs 3-2 and 3-3). In the process, ecological damage to the resource is repaired, and ecosystem structure and functions are recreated. A committee of the National Research Council (NRC) has noted that meeting this goal is difficult in urban ecosystems because the basic hydrologic, geomorphic, physical, biological, and biochemical processes have been forever altered. Nevertheless, limited systematic actions can be taken to enhance the system, including:

  • Developing buffers that provide protection to existing habitats.
  • Enhancing surface water management with facilities specifically designed to reduce adverse hydrologic and geomorphic impacts, to improve water quality, and to protect fish and wildlife habitat.
  • Undertaking stream corridor enhancement and restoration activities that will remediate existing problems or prevent future problems.
  • Implementing regulations and taking management actions that are aimed at reducing future adverse impacts of development.

Select measures that address the causes of degradation and the ecological functions identified in the study's conceptual model. EP 1105-2-70 (USACE, 2025), paragraph 4-3b(3), requires a conceptual model for Civil Works ecosystem restoration studies; hydrologic results should support the processes and objectives represented in that model.

Hydrologic Engineering Study Objectives and Outputs

EP 1105-2-70 (USACE, 2025), paragraphs 3-2, 4-2, and 4-3, provides explicit direction on measurable objectives, ecological success indicators, and existing and future without-project conditions. The hydrologic study should translate those objectives into the flow magnitude, frequency, timing, duration, and seasonal information needed by the hydraulic, geomorphic, and ecological analyses.

The study team should agree on the hydrologic information needed to evaluate each restoration objective. Relevant outputs may include flow hydrographs and peak flows associated with an annual exceedance probability (AEP), flow-duration statistics, and the timing and duration of ecologically important conditions. Provide HEC-HMS discharge results to a hydraulic model when the analysis requires water-surface profiles, inundation maps, depths, velocities, or the effects of backwater and structures (EM 1110-2-1416 (USACE, 1993), Chapters 5 and 6).

For restoration projects in which performance with low-flow conditions is critical, other indices may be of interest. For example, flow, velocity, and depth-duration functions may be desired for assessment of impacts of runoff on habitat development. From these, for example, the likely depths and durations of inundation during prime growing season of grasses can be found.
A hydrologic engineering study for stream restoration planning must assess watershed and channel conditions both with and without proposed changes. This will provide the information necessary to measure the effectiveness of different restoration alternatives.

Authority and Procedural Guidance

The following authorities have been used by USACE offices to restore aquatic habitats and mitigate development impacts:

  • WRDA 1996, Section 206. This legislation directs USACE to carry out aquatic ecosystem restoration and protection projects.
  • WRDA 1986, Section 1135. This authorizes USACE to modify existing project structures and operations to restore environmental quality. This subsequently was amended to include restoration project areas that are outside USACE project lands, but which were impacted by the project.
  • WRDA 1974, Section 22. With this, Congress gave USACE general authority to provide assistance to States and tribal governments with planning for the development, utilization, and conservation of water and related land resources. Recent amendments have expanded this assistance to include ecosystem planning.
  • WRDA 1992, Section 204. This authorizes USACE to protect, restore, and create aquatic habitat, including wetlands, in connection with dredging for authorized federal navigation projects.

Current project authority and applicability should be checked against EP 1105-2-70 (USACE, 2025), paragraph 2-3. The authorities above are an overview rather than a complete statement of current program requirements.

The following USACE guidance is particularly relevant to the hydrologic contribution to stream restoration:

  • EP 1105-2-70 (USACE, 2025), paragraphs 3-2, 3-3, 3-9, and 4-3 through 4-5, addresses ecological objectives, systems planning, monitoring and adaptive management, conceptual models, and comparison of with-project and future without-project conditions. It supports ER 1105-2-103 (USACE, 2023), Chapter 6, and applies to Civil Works aquatic ecosystem restoration; it does not apply to the Regulatory Program.
  • EM 1110-2-4000 (USACE, 2025), paragraph 7-14, directly addresses stream restoration. Paragraphs 7-3h and 7-4 cover the flow regime, channel-forming discharge, geomorphic assessment, and channel stability; identify hydrologic, hydraulic, and sediment inputs needed for the entire affected stream system.
  • EM 1110-2-1417 (USACE, 1994), Chapters 10 and 17, provides runoff-model calibration and frequency-based analysis guidance. Check rainfall/runoff frequency assumptions and test the model across the range of conditions relevant to the restoration objectives.
  • EM 1110-2-1416 (USACE, 1993), Chapters 5 and 6, addresses hydraulic model selection and river hydraulics, including structures. Use the required hydraulic analysis when local stages, culvert controls, backwater, or floodplain flow paths are important.
  • ECB 2026-1 (USACE, 2026), paragraphs 4c and 4d and section 8, addresses long-term hydrometeorological conditions for planning analyses that rely on stationarity-based frequency or duration relationships. Its applicability and exceptions must be considered for the study; the bulletin expires 9 January 2028.

The Natural Resources Conservation Service (NRCS) National Engineering Handbook Part 630 (NRCS, n.d.) provides current chapter-based hydrology references, and Part 654 (NRCS, 2007) provides stream restoration design material also cited by EM 1110-2-4000 (USACE, 2025), paragraph 7-14. That manual also cites Hydraulic Design of Stream Restoration Projects, ERDC/CHL TR-01-28 (Copeland et al., 2001), as a design reference. Retain SCS-era references where they document the historical Case Study's calculations.

Study Procedures

  1. Define measurable restoration objectives and a conceptual model with the ecological, hydraulic, geomorphic, and planning team. Identify which hydrologic variables support each success indicator.
  2. Characterize the watershed and stream system, including land use, observations, channel geometry, structures, sediment sources, and downstream controls. Establish existing and future without-project conditions.
  3. Select event simulations for flood-response questions and continuous simulations where seasonal flows, low flows, or duration statistics are required. Select methods and data appropriate to each use.
  4. Calibrate or otherwise check the basin and routing models against available flow, volume, timing, and seasonal information. Test uncertain parameters and initial conditions when direct observations are limited.
  5. Compare restoration alternatives with consistent upstream forcing and reporting locations. Change watershed runoff inputs only where the alternative actually changes watershed conditions; represent channel changes in the relevant routing or hydraulic model.
  6. Provide complete hydrographs and documented assumptions to hydraulic, sediment, and ecological analyses. Examine local and upstream water levels as well as downstream discharge, and assess channel stability and maintenance needs.
  7. Document sensitivity, residual uncertainty, and the measurements needed to evaluate project performance. Link those measurements to the monitoring and adaptive-management provisions applicable to the project.

Current HEC-HMS Muskingum-Cunge routing includes Eight Point and Tabular representations and configurable space-time discretization. Use Ensemble Analysis to organize alternative simulations and compare their full hydrographs; scenario counts alone do not establish probabilities.

For objectives involving seasonal conditions, current loss and baseflow methods support continuous water-balance modeling. Linear Deficit and Constant is an available event/continuous option, while the continuous-simulation calibration tutorials demonstrate Deficit and Constant and Soil Moisture Accounting workflows. Choose and verify canopy, evapotranspiration, subsurface, and warm-up settings as part of the complete model.

HEC-EFM (Ecosystem Functions Model) can relate hydrologic and hydraulic time series to study-defined ecological relationships. Coordinate ecological metrics and applicable model-review requirements with the study team (EP 1105-2-70 (USACE, 2025), paragraph 4-5c); reduced flood peaks alone do not establish restoration success.

For additional research context, ERDC SR-26-5 (Wiest et al., 2026), sections 2.2 through 2.6 and 3, reports workshop findings on restoration design and assessment in the USACE Regulatory Program. Participants compared natural channel design, floodplain/valley restoration, floodplain reconnection and expansion, and stabilization/habitat enhancements. They emphasized matching the approach to valley space, infrastructure, altered flow and sediment regimes, ecological objectives, and long-term maintenance needs. Sections 2.4 and 2.5 distinguish physical-process performance, ecological outcomes, and regulatory crediting decisions; they also identify floodplain inundation frequency, duration, and area as useful evaluation questions. For an HEC-HMS study, provide the flow time series needed by the hydraulic analysis to evaluate those conditions, rather than infer floodplain connectivity or ecological improvement from peak attenuation alone. The workshop evaluated existing approaches rather than developing a new design methodology. Its findings are research context; section 3.2 proposes future checklists and factsheets and does not establish a new mandatory design standard.