A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual

U.S. Army Corps of Engineers (USACE) | August 1st, 2008

The Ordinary High Water Mark (OHWM) is an approach for identifying the lateral limits of non-wetland waters. However, determining whether any non-wetland water is

The Ordinary High Water Mark (OHWM) is an approach for identifying the lateral limits of non-wetland waters. However, determining whether any non-wetland water is a jurisdictional “Water of the United States” (WoUS) involves further assessment in accordance with the regulations, case law, and clarifying guidance. In the Arid West region of the U.S., the most problematic Ordinary High Water (OHW) delineations are associated with the ephemeral/intermittent channel forms that dominate the Arid West landscape. This report presents a method for delineating the lateral extent of the non-wetland waters in the Arid West using stream geomorphology and vegetation response to the dominant stream discharge.

A Framework for Permitting Innovation in the Wastewater Sector

U.S. Environmental Protection Agency (USEPA) | December 1st, 2024

Our research and this report have focused primarily on how the National Pollutant Discharge Elimination System (NPDES) permitting process implementing the Clean Water Ac

Our research and this report have focused primarily on how the National Pollutant Discharge Elimination System (NPDES) permitting process implementing the Clean Water Act works for municipal wastewater utilities. However, the issues and potential strategies to improve how the permitting process addresses innovation are also relevant for other water management sectors such as stormwater, drinking water, watershed, wetland, and industrial wastewater management, along with other permitting contexts.

A Framework for Research Addressing the Role of Ammonia/Ammonium in the Sacramento-San Joaquin Delta and the San Francisco Bay Estuary Ecosystem

CALFED | April 13th, 2009

The Sacramento-San Joaquin Delta and the San Francisco Bay Estuary ecosystem has been drastically altered by human activity since at least the mid-1800s, leading to numer

The Sacramento-San Joaquin Delta and the San Francisco Bay Estuary ecosystem has been drastically altered by human activity since at least the mid-1800s, leading to numerous physical, chemical and biological changes [e.g., see Healey (2008) and Healey et al. (2008) for overviews]. Recent concerns include (1) the precipitous decline of four fish species that inhabit the Delta (collectively referred to as the pelagic organism decline, or POD) and (2) apparent major shifts in community composition of algae and higher trophic levels in the Delta and downstream in Suisun Bay. The four POD species of concern are delta smelt (longfin smelt), threadfin shad and striped bass. One of the potential causes of the POD and the community changes is the discharge of increasing concentrations of a combination of ammonia (NH3) and ammonium (NH4+) into the Delta ecosystem and eventually into Suisun Bay. For brevity, we hereafter abbreviate the ammonia/ammonium combination as ammonia/um. To address the potential for adverse effects of ammonia/um on the Bay-Delta ecosystem, a ammonia/um workshop was convened by the CALFED Science Program on 10 and 11 March 2009 in Sacramento, California. We participated as an expert panel and were charged with preparing a framework for research that will address the role of ammonia/um in the Bay-Delta ecosystem. In this report, we present our perception and interpretation of the major concerns related to ammonia/um in the Bay-Delta ecosystem; a conceptual framework of the major physical, chemical and biological drivers controlling the ecosystem (including POD populations); our assessment of the major research needs; and concluding remarks. For some research needs, we recommend specific types of research and provide literature citations; however, for other research needs we recommend general approaches for which targeted research will be determined later. In many ways, Bay-Delta research is breaking new ground by tackling a large-scale, complex freshwater-estuarine ecosystem affected by multiple, interactive stressors. Consequently, the Bay-Delta research program will establish a template for future research and management decisions in other hydrologically, biogeochemically, and trophically-similar systems, rather than relying on paths trodden by others.

A functional flows approach to selecting ecologically relevant flow metrics for environmental flow applications

River Research and Applications (Wiley) | January 8th, 2020

A geospatial analysis of water-quality threats from orphan wells in principal and secondary aquifers of the United States

Elsevier | May 10th, 2025

This work is the first multivariate geospatial investigation of orphan wells and groundwater resources on a national scale and identifies which aquifers are most susc

This work is the first multivariate geospatial investigation of orphan wells and groundwater resources on a national scale and identifies which aquifers are most susceptible to groundwater contamination from orphan wells.

A global dataset of surface water and groundwater salinity measurements from 1980–2019

Nature Portfolio (Springer Nature) | July 13th, 2020

Salinization of freshwater resources is a growing water quality challenge, which may negatively impact both sectoral water-use and food security, as well as bio

Salinization of freshwater resources is a growing water quality challenge, which may negatively impact both sectoral water-use and food security, as well as biodiversity and ecosystem services. Although monitoring of salinity is relatively common compared to many other water quality parameters, no compilation and harmonisation of available datasets for both surface and groundwater components have been made yet at the global scale. Here, we present a new global salinity database, compiled from electrical conductivity (EC) monitoring data of both surface water (rivers, lakes/reservoirs) and groundwater locations over the period 1980–2019. The data were assembled from a range of sources, including local to global salinity databases, governmental organizations, river basin management commissions and water development boards. Our resulting database comprises more than 16.3 million measurements from 45,103 surface water locations and 208,550 groundwater locations around the world. This database could provide new opportunities for meta-analyses of salinity levels of water resources, as well as for addressing data and model-driven questions related to historic and future salinization patterns and impacts.

A Guide to Ordinary High Water Mark (OHWM) Delineation for Non-Perennial Streams in the Western Mountains, Valleys, and Coast Region of the United States

U.S. Army Corps of Engineers (USACE) | August 14th, 2014

Federal regulations define the ordinary high water mark (OHWM) as “that line on the shore established by the fluctuations of water and indicated by physical cha

Federal regulations define the ordinary high water mark (OHWM) as “that line on the shore established by the fluctuations of water and indicated by physical characteristics such as a clear, natural line impressed on the bank, shelving, changes in the character of soil, destruction of terrestrial vegetation, the presence of litter and debris, or other appropriate means that consider the characteristics of the surrounding areas” (U.S. Congress 1986). Under Section 404 of the Clean Water Act (CWA), the OHWM defines the lateral extent of federal jurisdiction in non-tidal waters of the United States (WoUS) in the absence of adjacent wetlands (U.S. Congress 1977). Thus, accurate and consistent OHWM delineation practices are essential for proper implementation of the CWA. The dynamic nature of stream systems and fluvial processes presents challenges for OHWM delineation. Natural sources of variability in river and stream systems (e.g., climate, sediment supply, landscape position, etc.) are compounded by direct and indirect anthropogenic sources of variability (e.g., watershed alteration, dam emplacement and removal, climate change, etc.). Thus, it is challenging to impose a consistent measure of “ordinary” high flow conditions across systems in which the hydrology and geomorphology can vary greatly in both space and time. OHWM delineation in non-perennial (i.e., intermittent and ephemeral) streams can be especially challenging. The U.S. Army Corps of Engineers (USACE) defines intermittent streams as having “flowing water during certain times of the year, when groundwater provides water for stream flow. During dry periods, intermittent streams may not have flowing water. Runoff from rainfall is a supplemental source of water for stream flow” (USACE 2012). Ephemeral streams have “flowing water only during, and for a short duration after, precipitation events in a typical year. Ephemeral stream beds are located above the water table year-round. Groundwater is not a source of water for the stream,” and “[r]unoff from rainfall is the primary source of water for stream flow” (USACE 2012). In contrast to both intermittent and ephemeral streams, perennial streams have “flowing water year-round during a typical year. The water table is located above the stream bed for most of the year,” and “[g]roundwater is the primary source of water for stream flow” (USACE 2012). Given the less persistent streamflow regimes characteristic of non- perennial streams, particularly ephemeral systems, the characterization of ordinary high water flows is perhaps more challenging than in perennially flowing systems. Moreover, depending on climate, vegetation, and other related factors, the appearance of some OHWM indicators may vary greatly between wet and dry seasons or between relatively infrequent flow events, more so than in many perennial streams. Mountainous terrain can present additional challenges to OHWM delineation. For instance, the relatively steep and confined valleys in which mountain streams commonly flow can restrict the development of some alluvial features (e.g., flood-plains, bankfull benches, etc.) that are typical of low-gradient systems and that may help to identify the OHWM. Thus, in non-perennial mountain streams, it is often difficult to determine what constitutes ordinary high water and to interpret the physical and biological indicators established and maintained by ordinary high water flows. Challenges and inconsistencies pertaining to OHWM delineation practices are becoming increasingly relevant in mountainous parts of the western U.S. in light of expanding development. This increased pressure on fluvial systems highlights the need for accurate, consistent, and repeatable OHWM delineation practices in this region. These factors, combined with the particular challenges of OHWM delineation in non-perennial mountain streams, provided the impetus for developing this delineation guide. This guide presents the concepts, field indicators, and methods for assessing, delineating, and documenting the OHWM in non-perennial streams in the Western Mountains, Valleys, and Coast (WMVC) Region of the United States (Figure 1). The information presented here is based on the findings of Mersel et al. (2014) (discussed in Section 1.5) and on years of field observations and data gathering in the WMVC Region and in other regions of the U.S. by the authors and other contributing experts. The remainder of Section 1 provides background information regarding the concept of the OHWM and pertaining to stream hydrology and geomorphology in general. Section 2 discusses and provides examples of the specific field indicators used to identify the OHWM in non-perennial streams in the WMVC Region. Section 3 discusses field methods for delineating the OHWM and addresses additional techniques and lines of evidence that may help in problematic delineation scenarios. The information presented here is technical guidance and does not define, amend, or replace any existing regulations, laws, or legal guidance related to the OHWM or to the regulation of WoUS. Furthermore, determining whether any stream is a jurisdictional WoUS is beyond the scope of this document and involves further assessment in accordance with regulations, case law, and clarifying guidance. This guide pertains to non-perennial streams in the WMVC Region of the U.S., and while the information presented here may have a wider applicability to other regions or to perennial rivers within the WMVC Region, this has not been tested or validated. This manual serves as a companion to A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States (Lichvar and McColley 2008) as these two regions—the WMVC and the Arid West—are interspersed with one another. Best professional judgment is required to determine which manual is most appropriate for any given location within these two regions. The technical guidance presented here aims to provide an informed and consistent approach to OHWM delineation within the WMVC Region; however, OHWM delineation is not a precise practice. The OHWM can take on a variety of appearances and characteristics and may change over time due to natural or anthropogenic causes. Best professional judgment and consideration of the unique characteristics of each project site are always required.

A Guide to Water Quality Requirements under the Sustainable Groundwater Management Act

Stanford University | April 17th, 2019

California’s Sustainable Groundwater Management Act (SGMA) requires Groundwater Sustainability Agencies (GSAs) develop Groundwater Sustainability Plans (GSPs) that ach

California’s Sustainable Groundwater Management Act (SGMA) requires Groundwater Sustainability Agencies (GSAs) develop Groundwater Sustainability Plans (GSPs) that achieve sustainability within twenty years of Plan adoption. Meeting this goal requires GSAs to avoid causing any of the six undesirable results that are central to SGMA, including undesirable result number 4 (UR No. 4) – “significant and unreasonable degraded water quality” throughout the basin. Unlike most other undesirable results, UR No. 4 is the subject of robust federal, state and local regulatory regimes carried out by a number of different entities. While the State and Regional Water Resources Control Boards have the broadest responsibilities to protect groundwater quality, many other agencies also have relevant responsibilities. The other distinctive feature of UR No. 4 is that groundwater management that prevents chronic lowering of groundwater levels may be insufficient to prevent significant and unreasonable degradation of groundwater quality. For example, significant changes in groundwater pumping can potentially mobilize naturally occurring constituents or cause migration or expansion of contaminant plumes even when the extracted amount is within the basin’s sustainable yield. This Guide is intended to assist GSAs along with other agencies and stakeholders in understanding the meaning of UR No. 4, and to provide insights into how GSAs can successfully fulfill their legal responsibilities regarding groundwater quality. To avoid UR No. 4 under SGMA, this Guide recommends that GSAs do the following: 1. Understand the existing regulatory regime for groundwater quality and, as necessary, confer with entities that have regulatory authority over groundwater quality in their basins. (See Section 3 of this Guide). 2. Consider existing federal, state and local groundwater quality standards when developing groundwater quality minimum thresholds in their basins. Federal, state or local regulatory requirements were established after careful scientific study, legal review and procedural steps mandated by law. They are designed to protect public health and welfare, and they provide the clearest indication of the point beyond which there is a real risk of an undesirable result. (See Section 3.1). 3. Work closely with their Regional Water Quality Control Boards to address all groundwater quality issues. GSAs working in the Central Valley are especially encouraged to work with the Central Valley Regional Board to address salt and nutrient groundwater contamination. Programs in this region are continuing to evolve and will require that GSAs remain aware of changing regulatory requirements. Additionally, there are many groundwater quality monitoring efforts in this region that are generating a lot of groundwater quality data. These efforts should be aligned with any groundwater monitoring efforts being undertaken by GSAs. (See Sections 3.4.2 and 4.3.2). 4. Use existing groundwater quality data and information to (1) assess and prioritize groundwater quality issues in their basins, (2) meet requirements that GSPs include a description of current and historical groundwater conditions within the basin and (3) serve as either the basis for or a complement to local groundwater quality monitoring programs developed by GSAs. 5. Consider the following approach (discussed in Section 3.2) if they identify groundwater quality problems that either arose or were exacerbated after January 1, 2015: • Where there is a significant groundwater quality problem that is clearly under the purview of another agency, confer with that agency and seek to confirm a reasonable plan to address the groundwater quality problem. If such a plan exists, the water quality problem and the plan should be referenced in the GSP. Section 3 and Table 1 in the Guide provide information on existing regulatory programs and the agencies responsible for their enforcement. • Where a significant groundwater quality problem is not clearly under the purview of another agency, or the responsible agency is unable to confirm a reasonable plan to address the problem, confer with Regional or State Board staff, and perhaps affected parties, to identify a reasonable plan to address the problem. If no reasonable plan is identified, and remediating the problem is impractical, excessively wasteful of resources or otherwise infeasible, the GSA should include in the Plan an explanation of the problem and the reasons why remediation is impractical or infeasible. 6. Consider the following approach (discussed in Section 5) if they are planning projects or actions that may affect groundwater quality: • Assess the potential impacts that the projects or actions are likely to have on groundwater quality over time. If the GSA concludes that the proposed project or action could have unacceptable adverse impacts on water quality, GSAs should consider options such as revising the project to avoid or mitigate the project’s impacts or developing alternative projects that avoid water quality problems. • Ensure regulatory compliance for any GSP management actions (e.g., recharge projects, water banking) that have the potential to negatively impact water quality in their basins or adjacent basins. (Sections 3 and 5 provide information on regulatory requirements and considerations associated with groundwater recharge and active basin management, respectively.) 7. Develop supplemental groundwater monitoring networks where necessary. Many basins being managed under SGMA have significant water quality data gaps. Thus, GSAs in many basins will likely need to develop or expand local groundwater quality monitoring networks. Decisions to do so should be informed by (1) the extent and quality of existing groundwater quality in the region, (2) the level of groundwater development, (3) the severity of existing groundwater quality issues and their proximity to domestic or irrigation wells, public water supply sources or other vulnerable users, (4) current or proposed groundwater management actions or projects, (5) local resources, and (6) the hydrogeologic complexity of the basin. GSAs are not responsible for enforcing existing water quality standards or collecting data to support existing water quality programs. However, they are responsible for avoiding “significant and unreasonable” degradation of water quality in their basins. Working with federal, state and local water quality monitoring and enforcement entities will help GSAs understand groundwater quality issues in their basins, enabling them to develop GSPs that avoid UR No. 4.

A joint Gaussian process model of geochemistry, geophysics, and temperature for groundwater TDS in the San Ardo Oil Field, California, USA

Journal of Hydrology (Elsevier) | May 27th, 2025

A Menu of Fire Response Water Quality Monitoring Options and Recommendations for Water Year 2019 and Beyond

San Francisco Estuary Institute (SFEI) | July 2nd, 2018

In October 2017, the Tubbs Fire and the Nuns Fire burned 93,400 acres of the Mark West Creek and Santa Rosa Creek watersheds, killing 22 people, and incinerating approxim

In October 2017, the Tubbs Fire and the Nuns Fire burned 93,400 acres of the Mark West Creek and Santa Rosa Creek watersheds, killing 22 people, and incinerating approximately 7,000 structures. After the fires, many agencies worked together to deploy water and sediment related best management practices (BMPs) in the burn area (e.g., waddles, emergency hydroseeding, and filter systems on storm drains) and worked on removing contaminated debris and soil from burned properties. The City of Santa Rosa conducted water quality sampling to verify that the BMPs were working. Water quality samples were collected at selected sites before and after flow interacted with the BMP; the City was generally pleased with the results. Subsequently, the North Coast Regional Water Quality Control Board (Water Board) developed a preliminary monitoring design for WY 2018 to measure potential water quality impacts of the fires in relation to beneficial uses. Selected streams were sampled for parameters that could be compared to regulatory water quality criteria. The attachment contains a summary of the results for WY 2018. Based on this initial dataset, the apparent early success of the BMP program, and the soil clean-ups that have occurred, the focus going forward should be on monitoring larger-scale and longer-term impacts. This document outlines monitoring options for consideration for WY 2019 and beyond for four categories: Water Chemistry, Hydromodification, Geomorphic Response, and Ecology.