Friday, April 16, 2021

Comments on CDFW Instream Flow Recommendations

 Via E-mail to

RE: Comments on CDFW Draft Instream Flow Regime Recommendations for the Lower Ventura River (February 2021)

Dear Mr. Pert,

Thank you for the opportunity to provide comments on the Draft Instream Flow Regime Recommendations. This document has been long anticipated amongst stakeholders engaged in ongoing discussions in the watershed. During this time of unprecedented stress from increased population and climate change, guidance is clearly needed to secure instream flows to maintain riverine ecosystems in California. These diverse and delicate ecosystems support not only native fisheries, most of which are now threatened, but also provide for a quality of life and the very foundation of our economy. The endangered southern steelhead serves as an indicator for how well we manage our land and water, and these instream flow recommendations will help inform ongoing management of our watershed.

Flow Recommendations are difficult to understand

The CDFW Instream Flow Recommendations are the result of a combination of different analytical approaches developed over several years and published in multiple documents. This is necessary in developing a standard approach that applies to the entire State of California, but the result can be difficult to unravel. The outcome and implementation of these recommendations depend on a clear understanding of the approach and intent, not only within the scientific and regulatory communities, but most importantly amongst the diverse stakeholders that currently manage and benefit from the resource.

In the course of our review, two graphics were developed to more clearly illustrate the relationships between the various criteria, methodologies, and recommendations. These graphics and a description of the processes are attached with these comments and published online at

The Draft Ventura River Flow Recommendations were derived from Steelhead Passage Flows, Sensitive Period Indicators, and Steelhead Optimum Flows. (The other criteria were developed to provide context based on historical flows in the Ventura River Watershed.)

Therefore, the CDFW Instream Flow Recommendations are primarily based upon the physical properties of the river as determined by Field Methods. The exceptions are two cases where Steelhead Optimum Flows are applied, for Fall Pulse Flows in November (40cfs) and for Adult Migration (80cfs) in Reach 3 only. The latter two recommendations are arbitrary and inconsistent with the other field-based recommendations.

CDFW diverges from established watershed nomenclature

For these studies, CDFW redefined the river and reaches differently from established nomenclature in other watershed planning efforts. For example, much of Reach 3 and all of Reach 4 of CDFW’s “Lower Ventura River” falls within the “Upper Ventura River Groundwater Basin” as defined by the State Groundwater Management Act (SGMA). This nomenclature is likely to create confusion in discussions on implementation of the CDFW Instream Flows Recommendations.

Application of Instream Flow Recommendations is unclear

Stakeholders are confused as to the expectations of the Instream Flow Recommendations in the context of SGMA and other ongoing watershed concerns.

The Department understands these flows to be protective of steelhead and the habitat that supports them and recommends applying them across all water year types. In some cases, the recommended flows may not be available due to precipitation variability. When flows naturally fall below the flow recommendations for the lower Ventura River reaches 2,3, and 4, full natural flows should be maintained. Also, flows higher than the recommended criteria may be beneficial to the ecosystem and to steelhead.

It is unclear how to interpret this statement. Given that the existing condition falls short of the recommended flow in many water years, what is the meaning of “full natural flows should be maintained?” Does this refer to the Natural Flow developed in the Criteria Report (but not published in the Flow Recommendations?) (See comments below on Natural Flow)

Reaches 2/3/4 use different criteria for recommended flows

For the dry months, the differing flow recommendations in these reaches is an artifact of the field study protocols which produce slightly different results based on the varied streambed geometry. Indeed, the consistency of these results is a positive indicator of scientific rigor. A margin of error of 1cfs (6%) would be expected in the natural system, and this is also within the margin of error for the existing gage network (see comment below.)

Flow recommendations for the months of December-May are derived from the steelhead passage criteria (40/33 cfs) in reaches 2 and 3 respectively, while adult migration flows are applied only in reach 4 (80 cfs.) Apart from extractions at Foster park and inflows from Coyote Creek, these 3 reaches exist within the continuum of flows in the river, so 80 cfs in reach 4 would naturally translate to approximately the same flow in the reaches downstream.

Recognizing that these reaches are similar and connected, it may make more sense to apply a common denominator within these reaches to the entire reach as a whole. For example, the Sensitive Period indicator analysis for reaches 2, 3, and 4 resulted in 16, 14, and 15 cfs respectively. It is reasonable to conclude that a threshold of 14 or 15 cfs would indicate sensitivity for the reach as a whole.

The Natural Flows Database is flawed

The “Natural Flows” published in the Watershed Criteria Report are based on the Natural Flows Database for California computer model that attempts to predict unimpaired instream flows for the entire State of California. This model may be applicable to watersheds where snowpack and large reservoirs dominate, but appears to fall short in the groundwater dependent ecosystems of Southern California.

The CDFW Overview document states:

Natural Flows represent flows that would be present in the absence of water use or land use impacts to natural hydrology (Zimmerman et al. 2018). Natural Flows are determined using the estimated Natural Flows Database for California (Zimmerman et al. 2020). These data are used to calculate water month type, Ecosystem Baseflows, and Salmonid Habitat Optimum Flows.

The published literature regarding this computer model (Zimmerman 2017) include the disclaimer;

For some models, poor precision limited the sensitivity of our assessment, making
it impossible to determine whether deviation in flows from expected values was an artefact of the model or evidence of human-caused flow modification. This was 
particularly true for minimum and mean models in the dry season, when natural streamflows are low or absent and are controlled by physical processes that are not represented by basin- scale attributes.
For example, the data suggest that in the 
South Coast of Californiaunderstanding and mitigating the effects of inflated discharge in the summer may be critical

Here the authors admit a lack of understanding as to why the computer model predicts less instream flow than the “inflated discharge” evidenced by the stream gage records. In acknowledgement of this flaw, an “Appendix A” was added to the Watershed Criteria Report to provide an alternative Natural Flow estimation;

Natural Flows Database estimates are provided for every Watershed Criteria Report as part of the effort to produce a consistent statewide dataset. Where appropriate (relatively unimpaired) gage records are available, these site-specific data will be included as an appendix to the report. In these cases, the gage data are considered to replace the Natural Flows Database as an estimate of natural flow conditions.

Indeed, Ventura River flows for the dry months are grossly underestimated by the Natural Flows Database. One explanation may be the inability of the model to account for groundwater-surface water interactions, which are fundamental to the Ventura River. The flows published in Appendix A, derived from a statistical analysis of the “synthetic gage” data for the Ventura River, are significantly higher than those predicted by the Natural Flow database.

For this reason, the Draft Instream Flow Recommendation abandoned the Natural Flows Database, instead using the available historic gage data. Yet neither this document or the Watershed Criteria Report clearly explain the limitations of the Natural Flows information.

The Watershed Criteria Report as published states;

Natural Flows are the streamflows (in cfs) that would be expected with no human influence

Unfortunately, the perpetuation of “Natural Flows” in the CDFW publications is already tainting the public discourse. A recent OpEd published in the Ojai Valley News says:

“The new flow recommendation by the California Department of Fish & Wildlife is 15 cubic feet per second at Foster Park for summertime flows. This is dramatically different from the 1 cfs that the Department of Fish and Wildlife calculates for the same area from July to October of dry years as the “natural flows expected with no human influence” (Watershed Criteria Report No. 2020-01).”

Synthetic gage misrepresents Natural Flow

In place of the Natural Flows Database, these analyses use the synthetic least-impaired USGS gage Ventura R NR Ventura + Div 11118501 based on the period of record 1965– 2007

USGS gage Ventura R NR Ventura + Div , takes the historic USGS flow data and adds back the amount of water diverted through the surface diversion at the City of Ventura’s Foster Park wellfield. (Note that the surface diversion is a fraction of what the total wellfield extracts, and is currently out of commission.)

This “synthetic gage” data is used to develop many of the Watershed Criteria. The historic flow record from the past 40 years is useful in describing the general qualitative flow characteristics in the watershed such as Flow Variation, and to a lesser degree Functional Flows. However, the use of the synthetic gage as currently defined is extremely problematic when attempting to establish a baseline for unimpaired, or “Natural Flows.”

There are three primary concerns with the use of the historic USGS gage data;

First, this data is a record of surface flows just downstream from Foster Park from 1965-2007, which fundamentally represents the developed watershed. Most of the major modifications in the Ventura River Watershed occurred prior to 1965, including the construction of MatiIija Dam in 1948 and Casitas Dam in 1958. It is also important to note that by 1890, before stream gages existed, 4,000 acres of agriculture had already been developed in the Ojai Valley.

Second, a synthetic gage that solely accounts for a single surface diversion disregards the multitude of wells throughout the watershed upstream, all of which detract from the total discharge at Foster Park. The importance of the interaction between groundwater and surface water is recognized by the State of California in the Sustainable Groundwater Management Act. Studies and governance are underway to better define these effects within the Ventura River Watershed. Coordination with the State Water Board’s surface water/groundwater model analysis of unimpaired flows would have been helpful in providing a more robust baseline for instream flows.

Third, stream gaging was historically focused on recording flood events rather than maintaining low flow accuracy. Each flood causes geomorphic alterations to the streambed profile which necessitates re-staging, or re-calibrating, the gages for accuracy. However, until recently very little attention was given to low flows, which are notoriously difficult to measure accurately (i.e. the margin of error may meet or exceed the measured flow.) Other uncontrolled variables such as vegetation growth or human activity can significantly affect gage accuracy. Unfortunately, these variables are not quantifiable in hindsight, so the low flow record has a very high margin of error.

It is important to recognize that the “synthetic gage” does serve as a baseline for the current condition based upon the hydrology of the past 40 years. This 20th century baseline will become most relevant in the coming decades with the increasing pressures of population growth and climate change, as well as to monitor progress with enhanced watershed management.

However, by no means does the synthetic gage represent “the flow that would be present in the absence of land use and water diversion impacts to natural hydrology.” Indeed, it is not only misleading to call these “Natural Flows,” this also undermines any discussion of maintaining or enhancing base flows in the river.

Most importantly, the “Natural Flows” assessment perpetuates the Shifting baseline syndrome“an incremental lowering of standards that results with each new generation lacking knowledge/ observation of the historical (or previous) condition of the environment being observed.”


  • Consolidate flow recommendations for the similar and contiguous reaches 2, 3, and 4.
  • Revise the flow recommendations based on Steelhead Optimum Flows to maintain consistency with flow recommendations based on field methods.
  • Eliminate the flawed Natural Flows Database results from the Criteria Report and revise Natural Flows to reflect the stream gage analysis used in the Flow Recommendations report.
  • Replace the term “Natural Flows” with “Historic Flows” to better represent conditions in the watershed.
  • Update the Natural Flow Criteria as more information comes available from the State Water Board analysis of groundwater-surface water interactions and estimates of unimpaired flow.

We appreciate the opportunity to comment on the Draft Instream Flow Regime Recommendations for the Lower Ventura River and hope these comments are helpful in finalizing these documents.


A.Paul Jenkin
Coordinator, Matilija Coalition
Surfrider Foundation - Ventura County Chapter

On this blog:

Understanding CDFW Instream Flow Recommendations

Ecosystem flows

In the news:

   Ojai leaders don't go with the flow, Ojai Valley News, 5 March 2021 

“These humongous flows by Fish and Wildlife would totally disrupt life in the Ojai Valley,” said Rapp, adding he was particularly alarmed by the agency’s statement that full, natural flows should be maintained when flows fall below the recommendations. “That’s a huge impact. That means for many months of the year, no one should pump their wells, or if someone has diversion rights they should not divert water from the river.”

The decision on what type of instream flow regime is necessary to support a healthy Ventura River is essentially a scientific one, and will not, and should not, be decided by authors of letters to the editor or guest columnists. However, the political will to support and implement whatever scientifically defensible instream flow regime is identified, is very much a matter of public awareness and understanding. Ultimately, the question raised by the current controversy over dividing the waters of the Ventura River is, “What kind of a community do we want to be?” The residents of the Ojai and Ventura River Valleys have an opportunity to set an example for other communities in California and beyond. 

The new flow recommendation by the California Department of Fish & Wildlife is 15 cubic feet per second at Foster Park for summertime flows. This is dramatically different from the 1 cfs that the Department of Fish and Wildlife calculates for the same area from July to October of dry years as the “natural flows expected with no human influence” (Watershed Criteria Report No. 2020-01). 

Three of the largest water users in the Ventura River Watershed — the city of Ventura, Ventura River Water District and Meiners Oaks Water District — have all sent response letters to CDFW regarding the recommendations. All three letters state there’s not enough water in the river to meet Fish and Wildlife’s recommendations.

“The flows that they’ve recommended for steelhead are not available in the river most of the time, so they set these recommended flows that we cannot achieve,” said James Kentosh, vice president of Meiners Oaks Water District.

CDFW’s recommended flows significantly exceed natural, historic flows during all but four months of even the wettest of years, Kentosh told the Ojai Valley News. “If every human being stopped using water in the valley, those flow recommendations would still only be enough a fraction of the time,” he said.  Furthermore, the amounts of water necessary to supplement natural flows to reach recommended flows are too large, according to Bruce Kuebler, board president of VRWD.