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 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. 

A multi-isotope (B, Sr, O, H, and C) and age dating (3H–3He and14C) study of groundwater from Salinas Valley, California: Hydrochemistry, dynamics, and contamination processes

American Geophysical Union (AGU) | January 31st, 2002

The chemical and isotope (11B/10B, 87Sr/86Sr, 18O/16O, 2H/H, 13C/12C, 14C, and 3He/3H) compositions of groundwater from the upper aquifer system of the Salinas Valley in

The chemical and isotope (11B/10B, 87Sr/86Sr, 18O/16O, 2H/H, 13C/12C, 14C, and 3He/3H) compositions of groundwater from the upper aquifer system of the Salinas Valley in coastal central California were investigated in order to delineate the origin and processes of groundwater contamination in this complex system. The Salinas Valley has a relatively deep, confined ‘‘400- foot’’ aquifer, overlain by a ‘‘180-foot’’ aquifer and a shallower perched aquifer, all made up of alluvial sand, gravel and clay deposits. Groundwater from the aquifers have different 14C ages: fossil (14C = 21.3 percent modern carbon (pmc) for the 400-foot aquifer and modern (14C = 72.2–98.2 pmc) for the 180-foot aquifer. Fresh groundwater in all aquifers is recharged naturally and artificially through the Salinas River. The two modes of recharge can be distinguished chemically.We identified several different saline components with distinguishable chemical and isotopic fingerprints. Saltwater intrusion in the northern basin has C1 concentrations up to 1700 mg/L, a Na/Cl ratio less than seawater, a marine Br/Cl ratio, a Ca/Cl ratio greater than seawater, d11B between +17 and +38% and 87Sr/86Sr between 0.7088 and 0.7096. Excess dissolved Ca, relative to the expected concentration for simple dilution of seawater, correlates with 87Sr/86Sr ratios, suggesting base exchange reaction with clay materials. (2) Agriculture return flow is high inNO3 and SO4, with a 87Sr/86Sr = 0.7082,d11B = 19% and d13C between 23 and 17%. The 3H–3He ages (5–17 years) and 14C data suggest vertical infiltration rates of irrigation water of 3–10 m/yr. (3) Nonmarine saline water in the southern part of the valley has high total dissolved solids up to 3800 mg/L, high SO4, Na/Cl ratio >1, d11B between +24 and +30%, and 87Sr/86Sr = 0.70852. This groundwater may have acquired its geochemical signature from leaching of sedimentary rocks associated with the Coast Range marine deposits of Mesozoic to early Cenozoic age. The combination of different geochemical and isotopic fingerprints enables us to delineate the impact of salt sources in different areas of the valley and to reconstruct the origin of the SO4-enriched NO3-depleted saline plume that is located west of the city of Salinas. We suggest that the latter is derived from a mixture of different natural saline waters rather than from anthropogenic contamination.

A multi-scale approach for identification of potential pesticide use sites impacting vernal pool critical habitat in California

Science of the Total Environment (Elsevier) | October 17th, 2022

Spatially explicit ecological risk assessment (ERA) requires estimating the overlap between chemical and receptor distribution to evaluate the potential impacts of exposu

Spatially explicit ecological risk assessment (ERA) requires estimating the overlap between chemical and receptor distribution to evaluate the potential impacts of exposure on nontarget organisms. Pesticide use estimation at field level is prone to error due to inconsistencies between ground-reporting and geospatial data coverage; attempts to rectify these inconsistencies have been limited in approach and rarely scaled to multiple crop types. We built upon a previously developed Bayesian approach to combine multiple crop types for a probabilistic determination of field-crop assignments and to examine co-occurrence of critical vernal pool habitats and bifenthrin application within a 5-county area in California (Madera, Merced, Sacramento, San Joaquin, and Stanislaus counties). We incorporated a multi-scale repeated sampling approach with an area constraint to improve the delineation of field boundaries and better capture variability in crop assignments and rotation schemes. After comparing the accuracy of the spatial probabilistic approach to USDA Census of Agriculture crop acreage data, we found our approach allows more specificity in the combination of crop types represented by the potential application area and improves acreage estimates when compared to traditional deterministic approaches. In addition, our multi-scale sampling scheme improved estimates of bifenthrin acreage variability for co-occurrence analysis and allowed for estimates of crop rotations that were previously uncaptured. Our approach could be leveraged for more realistic, spatially resolved exposure and effects models both in and outside of California.

A Practitioner’s Guide to Instream Flow Transactions in California

American Rivers | March 1st, 2016

The purpose of this guide is to help water right holders –and those assisting them – understand their options for keeping water instream in California. Th

The purpose of this guide is to help water right holders –and those assisting them – understand their options for keeping water instream in California. This guide briefly describes some of the most common types of instream flow transactions (i.e., methods for restoring flow for environmental purposes), and discusses in detail how to navigate the process of completing an instream flow dedication by changing a water right, as permitted by Water Code Section 1707. The intended audience for this document includes both water rights holders and practitioners, such as staff for land trusts, water trusts, Resource Conservation Districts (RCDs), and other organizations. This guide focuses on instream dedications via the change petition process administered by the State Water Resources Control Board (State Water Board). Other publications – for example, the Trust for Public Land’s Water Acquisition Handbook (2003) – provide a more general overview of acquiring water for environmental purposes in California. This guide will provide a description of the change petition process, and offer advice on how to navigate, troubleshoot, and work in partnership with the State Water Board and other natural resource agencies to complete an instream flow dedication.

A Preliminary Study of the Effects of Water Circulation in the San Francisco Bay Estuary

U.S. Geological Survey (USGS) | July 15th, 1970

A Salton Sea Chronology (Prehistory-2015)

U.S. Bureau of Reclamation (USBR) | January 14th, 2016

A Summary of Water-Quality and Salt Marsh Monitoring, Humboldt Bay, California

U.S. Geological Survey (USGS) | September 16th, 2022

This report summarizes data-collection activities associated with the U.S. Geological Survey Humboldt Bay Water-Quality and Salt Marsh Monitoring Project. This work was u

This report summarizes data-collection activities associated with the U.S. Geological Survey Humboldt Bay Water-Quality and Salt Marsh Monitoring Project. This work was undertaken to gain a comprehensive understanding of water-quality conditions, salt marsh accretion processes, marsh-edge erosion, and soil-carbon storage in Humboldt Bay, California. Multiparameter sondes recorded water temperature, specific conductance, and turbidity at a 15-minute timestep at two U.S. Geological Survey water-quality stations: (1) Mad River Slough near Arcata, California (U.S. Geological Survey station 405219124085601) and (2) Hookton Slough near Loleta, California (U.S. Geological Survey station 404038124131801). At each station, discrete water samples were collected to develop surrogate regression models that were used to compute a continuous time series of suspended-sediment concentration from continuously measured turbidity. Data loggers recorded water depth at a 6-minute timestep in the primary tidal channels (Mad River Slough and Hookton Slough) in two adjacent marshes (Mad River marsh and Hookton marsh). The marsh monitoring network included five study marshes. Three marshes (Mad River, Manila, and Jacoby) are in the northern embayment of Humboldt Bay and two marshes (White and Hookton) are in the southern embayment. Surface deposition and elevation change were measured using deep rod surface elevation tables and feldspar marker horizons. Sediment characteristics and soil-carbon storage were measured using a total of 10 shallow cores, distributed across 5 study marshes, collected using an Eijkelkamp peat sampler. Rates of marsh edge erosion (2010–19) were quantified in four marshes (Mad River, Manila, Jacoby, and White) by estimating changes in the areal extent of the vegetated marsh plain using repeat aerial imagery and light detection and ranging (LiDAR)-derived elevation data. During the monitoring period (2016–19), the mean suspended-sediment concentration computed for Hookton Slough (50±20 milligrams per liter [mg/L]) was higher than Mad River Slough (18±7 mg/L). Uncertainty in mean suspended-sediment concentration values is reported using a 90-percent confidence interval. Across the five study marshes, elevation change (+1.8±0.6 millimeters per year [mm/yr]) and surface deposition (+2.5±0.5 mm/yr) were lower than published values of local sea-level rise (4.9±0.8 mm/yr), and mean carbon density was 0.029±0.005 grams of carbon per cubic centimeter. From 2010 to 2019, marsh edge erosion and soil carbon loss were greatest in low-elevation marshes with the marsh edge characterized by a gentle transition from mudflat to vegetated marsh (herein, ramped edge morphology) and larger wind-wave exposure. Jacoby Creek marsh experienced the greatest edge erosion. In total, marsh edge erosion was responsible for 62.3 metric tons of estuarine soil carbon storage loss across four study marshes. Salt marshes are an important component of coastal carbon, which is frequently referred to as “blue carbon.” The monitoring data presented in this report provide fundamental information needed to manage blue carbon stocks, assess marsh vulnerability, inform sea-level rise adaptation planning, and build coastal resiliency to climate change.

A Summary of Water-Quality and Salt Marsh Monitoring, Humboldt Bay, California

U.S. Geological Survey (USGS) | September 16th, 2022

This report summarizes data-collection activities associated with the U.S. Geological Survey Humboldt Bay Water-Quality and Salt Marsh Monitoring Project. This work was u

This report summarizes data-collection activities associated with the U.S. Geological Survey Humboldt Bay Water-Quality and Salt Marsh Monitoring Project. This work was undertaken to gain a comprehensive understanding of water-quality conditions, salt marsh accretion processes, marsh-edge erosion, and soil-carbon storage in Humboldt Bay, California. Multiparameter sondes recorded water temperature, specific conductance, and turbidity at a 15-minute timestep at two U.S. Geological Survey water-quality stations: (1) Mad River Slough near Arcata, California (U.S. Geological Survey station 405219124085601) and (2) Hookton Slough near Loleta, California (U.S. Geological Survey station 404038124131801). At each station, discrete water samples were collected to develop surrogate regression models that were used to compute a continuous time series of suspended-sediment concentration from continuously measured turbidity. Data loggers recorded water depth at a 6-minute timestep in the primary tidal channels (Mad River Slough and Hookton Slough) in two adjacent marshes (Mad River marsh and Hookton marsh). The marsh monitoring network included five study marshes. Three marshes (Mad River, Manila, and Jacoby) are in the northern embayment of Humboldt Bay and two marshes (White and Hookton) are in the southern embayment. Surface deposition and elevation change were measured using deep rod surface elevation tables and feldspar marker horizons. Sediment characteristics and soil-carbon storage were measured using a total of 10 shallow cores, distributed across 5 study marshes, collected using an Eijkelkamp peat sampler. Rates of marsh edge erosion (2010–19) were quantified in four marshes (Mad River, Manila, Jacoby, and White) by estimating changes in the areal extent of the vegetated marsh plain using repeat aerial imagery and light detection and ranging (LiDAR)-derived elevation data. During the monitoring period (2016–19), the mean suspended-sediment concentration computed for Hookton Slough (50±20 milligrams per liter [mg/L]) was higher than Mad River Slough (18±7 mg/L). Uncertainty in mean suspended-sediment concentration values is reported using a 90-percent confidence interval. Across the five study marshes, elevation change (+1.8±0.6 millimeters per year [mm/yr]) and surface deposition (+2.5±0.5 mm/yr) were lower than published values of local sea-level rise (4.9±0.8 mm/yr), and mean carbon density was 0.029±0.005 grams of carbon per cubic centimeter. From 2010 to 2019, marsh edge erosion and soil carbon loss were greatest in low-elevation marshes with the marsh edge characterized by a gentle transition from mudflat to vegetated marsh (herein, ramped edge morphology) and larger wind-wave exposure. Jacoby Creek marsh experienced the greatest edge erosion. In total, marsh edge erosion was responsible for 62.3 metric tons of estuarine soil carbon storage loss across four study marshes. Salt marshes are an important component of coastal carbon, which is frequently referred to as “blue carbon.” The monitoring data presented in this report provide fundamental information needed to manage blue carbon stocks, assess marsh vulnerability, inform sea-level rise adaptation planning, and build coastal resiliency to climate change.