Draft Groundwater-Surface Water Model of the Ventura River Watershed

Date: April 1, 2022

To: Kevin DeLano, SWRCB

From: Paul Jenkin, Surfrider Foundation

RE: Comments on SWRCB Draft VRW GW-SW Model Report

The State Water Resources Control Board (State Water Board) Division of Water Rights and Los Angeles Regional Water Quality Control Board (collectively, the Water Boards) have published the Draft Groundwater-Surface Water Model of the Ventura River Watershed (VRW GW-SW Model) and Draft Model Documentation Report for the Groundwater- Surface Water Model of the Ventura River Watershed (VRW GW-SW Model Documentation Report).

This modeling effort has been accomplished with the SWRCB team and consultants with the goal of creating a tool that may be used in making water management decisions within the Ventura River watershed. To this end, we have reviewed the document and provide the following comments to help raise important questions and direct further refinement of the model. Quotes from the document are italicized.

First of all, and most importantly, it is recognized that all models are approximations, and the results of those approximations are heavily dependent on the available data. The report discusses model limitations:

All models and model results are subject to uncertainty, including model framework uncertainty due to incomplete scientific understanding of the system and necessary system simplifications, and model input uncertainty due to data measurement errors and data gaps (U.S. EPA, 2009). However, California Department of Water Resources (DWR, 2016b) states:

While models are, by definition, a simplification of a more complex reality, they have proven to be useful tools over several decades for addressing a range of groundwater problems and supporting the decision-making process. Models can be useful tools for estimating the potential hydrologic effects of proposed water management activities.

In order for the model to be a “useful tool”, it must accurately represent the physical reality it is attempting to replicate. In this case the modelers have been transparent in the limitations of the model and their manipulation of certain variables in order to calibrate the model to achieve a reasonable match with the field data. However, in generating output that appears to be more accurate in certain circumstances while not in others, this artificial calibration may give a false sense of the model’s accuracy and hence its usefulness in “estimating the potential hydrologic effects of proposed water management activities.”

At this point it is clear that the model is still a draft, and additional calibration will be required to more accurately match the physical systems being modeled. This will be important for implementing various management scenarios in the model, otherwise the errors in the model will outweigh any small changes in climate or water management.

The intent of this review is to provide constructive feedback such that the model may be improved upon to further its usefulness in the watershed. The following observations are based upon review of the report and some limited use of the visualization tool. (The visualization tool does not have full capabilities in older versions of Excel). These comments are focused on the main stem of the Ventura River and headwaters in Matilija Creek.

The Model underestimates the presence of surface flow

A fundamental question in assessing the accuracy of groundwater/surface water interaction is;

How well does the GW/SW Model represent rising groundwater, particularly in the “Live Reach” upstream of Foster Park?

In this gaining reach, the town of “Casitas Springs” was named for the perennial flows, i.e. “springs” along this reach of the Ventura River. However, the model calibration/validation results predict greater dryness than the field observations for this section of the river.

Fig 5.26 shows surface flow Wet-Dry Mapping comparing the model predictions with data measured in the field. This figure shows that the model predicts drying in the live reach when it was not observed during WY 2009 and 2010.

The model also predicts a greater spacial extent of drying, particularly upstream of the San Antonio creek confluence and downstream of the Foster Park gage. It is possible that this is an artifact of the model segments which may not coincide with the actual physical geographic boundaries. However, these boundaries are marked by bedrock outcrops that force groundwater to the surface and are integral to the representation of physical processes.

This anomaly in the model appears to carry into the Unimpaired Flow scenario which predicts drying in the “wet reach” in the absence of any pumping or diversion. This result is unexpected given the geology and historic record of perennial flows in this reach.

The sensitivity analysis discusses the response of the model to coefficient changes and reveals the importance of groundwater coefficients especially in areas of rising groundwater. The report states that:

The modeled wet-dry mapping is primarily a result of the groundwater level calibration coupled with streambed conductivities and widths, that together determine the extent of the gaining and losing reaches through the SFR package. During the calibration process, the wet-dry mapping was assessed and adjustments were made to the streambed conductivities to achieve better match. These adjustments were relatively minor; larger adjustments would feed back into the groundwater and surface water calibrations, requiring additional iterations. (p162)

This suggests that streambed conductivity was the sole coefficient adjusted to try to achieve a match with the data. Meanwhile, the model results derive from the complex relationship between all the other surface and groundwater inputs from the top of the watershed down, each of which is subject to assumptions and potential error. As suggested, additional iterations will be required to better calibrate the model.

Hydraulic conductivity

The hydraulic conductivity constant, Kx/y, determines the rate of groundwater flow downhill through the basin. As shown in Figure 5.11a, the main stem Ventura River is modeled with a hydraulic conductivity coefficient an order of magnitude above other regions in the watershed (i.e. 1250 ft/day vs 150 ft/day). This assumption was based on a single test done at Foster Park, and applied to the entire Upper Ventura River Groundwater Basin upstream.

Given a similar geology, why is the Upper Ventura River Groundwater basin conductivity an order of magnitude great than the Ojai basin?

When estimates of hydraulic parameters are available for the regions of the modeled physical hydrogeologic system, the corresponding values of those parameters in the model should be similar, but do not have to be identical. There are two reasons for this. First, the estimates themselves have associated errors, often of an order of magnitude. Second, when these estimates are based on hydraulic tests, the volume of soil or rock stressed by the test is often smaller than the volume in the model for which the parameter applies. In that case, the input hydraulic conductivity or transmissivityrequired to calibrate the model is often larger than the measured value due to the scale effect. (p209)

Hydraulic conductivity can be hard to estimate but has a significant influence on the groundwater model. The assumption of homogeneous high conductivity throughout the groundwater basin underlying the main stem Ventura River results in the model exhibiting rapid underflow through this basin which in turn has a significant effect on predicted groundwater levels. Additional monitoring wells and hydrogeologic testing are needed to improve understanding of the transmissivity of this basin.

Calibrating to Flow Gage Data:

A major concern is that;

Uncertainty from PRMS-portion of the simulation will propagate and influence groundwater recharge estimates.

Flow gage data is perhaps the most important parameter used in calibration of the groundwater- surface water model. As acknowledged in the report, the accuracy of flow data decreases at lower flows. One reason for this is that the majority of the stream gages were installed and maintained by the Ventura County Flood Control District as part of their ALERT flood warning system. These gages were neither intended nor maintained to provide low flow data, as their purpose was for flood control. The two possible exceptions are the USGS gages at Foster Park (608) and Matilija Creek (602) which have historically received more regular re-staging during the dry months, but even at Gage 608 measurements during the low flow periods (i.e., summers) are of Poor quality with errors anticipated to be greater than 8% (p158)

Although the USGS gages provide the most accurate flow data, the model calibration relied heavily on the County flow gages. The resulting modeling error statistics show that the greatest errors occur at the USGS gages, Matilija Creek (602) and Foster Park (608).

The report discussion of calibration and error analyses reveal the difficulty in achieving good correlation for all sites over the full range of water year types.

Agreement of the model results during low-flow periods (i.e., summer and fall) is generally good, with monthly average flows being well predicted down to approximately 1 cfs at most locations. Exceptions are noted in years with higher summer flows (e.g., 1995, 1998, 2005, and 2006) where the model underpredicts the summer flows. Adjusting calibration parameters to correct these years resulted in poorer prediction of the summer flows in the more typical and lower flow years. Since the lower flows are more critical for many drivers in the watershed (e.g., fish passage), model calibration was focused on obtaining better predictions in the lower flow years. The effect of this on the summer volume errors is discussed in more detail in Section 5.4.1.2. (p184)

The mean errors in Table 5.6 are negative at all gage locations, indicating a general bias in the model (i.e., a consistent underestimation of flows at all locations). Additional evaluation of the mean and RMS errors indicates that the largest summer streamflow errors are during the wet years with higher stream flows. This is a result of prioritizing the accuracy of years with lower flows during the calibration process, since the lower flow years are critical with respect to many of the project goals (e.g., evaluation of fish passage). (p198) 

 Relative summer volume errors (as percentages) are misleadingly high due to low measured flow rates and are poor metrics for assessing calibration performance for ephemeral systems that can result in a zero in the denominator. Absolute errors (i.e., in cfs) are more appropriate. For example, at Foster Park (Gage 608) a relative error of - 47.1% corresponds to mean and root-mean-square (RMS) errors of only -3.5 cfs and 5.9 cfs, respectively. Additionally, these flow rate errors are dominated by high runoff years. Excluding the six years with >50,000 AF of run-off at Foster Park results in the mean and RMS errors decreasing to -1.4 cfs and 2.6 cfs, respectively. Furthermore, in the Very Dry and Dry years the mean and RMS errors decrease to -0.3 cfs and 1.3 cfs, respectively. (p200)

Note that although errors of 1-3 cfs sound minimal, this is actually very significant in a system that is now often running dry.

Because of difficulties modeling varied flow regimes, the model was calibrated to low flow gage data. However, because gage accuracy decreases at lower flows, this strategy may introduce a significant error. It may be prudent to first calibrate the model to the more accurate gage data at Matilija Creek (602) and Foster Park (608) for moderate flow years. In theory the modeling coefficients should not vary significantly under different flow regimes. Developing a model that behaves well in “normal” conditions and then “stress testing” and fine tuning the model so that it also performs well in dry conditions would result in a more robust representation of the physical system. Calibration to dry year flow data results in the dry bias seen in the Wet-Dry mapping discussed above.

The Matilija Creek at Matilija Hot Springs (602) USGS gage is perhaps the most accurate stream flow gage in the watershed as it is controlled with a concrete weir and regularly staged. This gage may be more appropriate for model sensitivity and calibration than the North Fork Matilija gage.

The model underestimates summer flow volumes (June-Sept) at Gage 602 by 42%. Any error in this reach, which is the primary inflow to the mainstem Ventura River during the hot summer months, will be amplified in the downstream groundwater/surface water model.

Are diversions in Matilija Creek adequately accounted for?

The Visualization Tool for Gage 603A/Upper Matilija Creek reveals that the model Base Case tracks closely with Unimpaired flow for the dry months, while the gage often reads lower. The model overpredicts flows at Gage 603. There are irrigated lands and residential parcels in the canyon all of which draw from the creek or shallow wells. Most of these appear to be included in the model. Have the groundwater and surface water diversions in Matilija Canyon been adequately estimated in the model?

Are diversions in the Kennedy Reach adequately accounted for?

This reach has a number of wells and at least two surface diversions that collectively have the capacity to pump at a rate greater than average streamflow input to shallow alluvium in this reach during the summer months. However, the model predicts very little effect (0.2-0.7 cfs) on surface flows from eliminating pumping and diversion in the Unimpaired Flow condition.

At Gage 607 (Figure 5.16), the measurement indicates flows decrease to zero in most years; whereas, the model typically decreases to approximately 1 cfs in most years. The discrepancy is likely due to not including details of the hydraulic structure related to the Robles diversion (i.e., the embankment and gate structure that blocks the Ventura River) in the VRW GSFLOW Model. This structure would result in pooling of water and additional streamflow losses (through infiltration) upstream of the diversion structure. While these local details are not fully captured in the VRW GSFLOW Model, the additional water passing the diversion location during low flows infiltrates and is lost from the stream shortly downstream.

Comparing the Visualization Tool Base Case with Gage 607 data shows no clear trend in the errors, but as noted the river often goes dry upstream of Robles Diversion. A dry river within the shallow alluvium of the Kennedy Reach while the model predicts 1cfs or greater indicates that closer attention to pumping and diversion in this reach may be helpful.

It is important to be able to accurately model the flows entering the Ventura River from the upper watershed, especially during summer months, as this affects the water balance in the groundwater basin downstream during times of high irrigation demand. However, the surface flow modeling is not consistent with the gage data. The model generally overpredicts flows at Gage 603, underpredicts flows downstream at Gage 602, and underpredicts drying at Gage 607. These observations describe inconsistencies in modeled stream flows that should be resolved in order to provide a more accurate assessment of inflows into the groundwater basin.

Assumptions for Arundo donax:

The model assumes that the extent of riparian vegetation is fixed in time. This neglects the effects of Arundo eradication efforts, reduction in vegetation following storm events in wet years, and potentially increased ET following wet years as vegetation reestablishes. This limitation would primarily affect dry season low-flow periods.

According to the County of Ventura, over 270 acres of Arundo donax have been removed from an area encompassing 1,200 acres of the watershed encompassing Matilija Canyon and the Upper Ventura River during the period 2006 to the present. Most of this was in Matilija Canyon as shown in red in Figure 4.10.

Discussion during the workshop indicated that the model applies ET rate of 24 ft/yr for Arundo, with reference to CalIPC 2011. (For comparison, turf grass exhibits ET of 3-4 AF per acre.). Using a conservative estimate for Arundo ET of 20AF /acre, this would theoretically yield 270acres X 20AFY = 5400 AFY. This translates into 5400AFY/365days = 7 cfs. (An equivalent removal of turf grass would yield around 1 cfs)

It is important to note that 7 cfs is a significant flow augmentation in a system that often experiences flows of 2-3 cfs or less, yet stream gage observations do not reflect any substantial change in flow in the years following arundo removal.

This suggests that the model overestimates ET losses from the upper watershed, which would reduce predicted instream flows. This may be a source of error in the predicted flows at Matilija Creek at Matilija Hot Springs (602).

Matilija Dam:

additional errors in the model results may result from uncertainties in estimating release volumes from Matilija Reservoir (Section 3.5.1).

 If the SWRCB proposes to run a scenario for dam removal, this aspect of the model will need close attention. It is important to note that Matilija Dam spillway elevation has been set at 1095 and operated as run of the river except in cases of releases for diversion at Robles. The model documentation and discussions are unclear as to the assumptions made on the operation of Matilija Dam. A modeling scenario for dam removal will primarily depend on predicted changes in ET for the reservoir reach upstream. Dam removal will convert a large area of riparian and lacustrine habitat to upland habitat, with an associated decrease in ET. Additional changes will occur in the main stem Ventura River from renewed sand, gravel, and cobble supply which will alter the characteristics of the stream bed and alluvium. (This also applies to a post-Thomas Fire scenario.)

When constructed in 1947, Matilija Reservoir originally had an active storage volume of 7,000 AF. However, due to sedimentation and lowering (or ‘notching’) of the dam, the active volume has decreased substantially as indicated Table 3.1. Over the modeling period, the active storage volume at full pool decreased from 930 AF to 270 AF. This changing storage capacity during the modeling period is not implemented into the model. In the model the elevations of the lake cells were lowered to create a volume of 1,503 AF with a spillway elevation of 1,095 ft based on information on Ventura County Public Works Agency website. Although this is not consistent with information in Table 3.1 the effect in the model is primarily to increase dead storage with anticipated negligible effects on streamflow.

Outflows from Matilija Reservoir were modeled as a combination of overflows over the dam crest and specified releases (Section 3.5.1), each into a downstream stream segment representing the dam spillway. (p80)

Historically, the CMWD would release water from Matilija Reservoir to enable additional diversions downstream through the Robles Canal to Lake Casitas. Information on these releases is limited and had to be estimated for the modeling period.

Reservoir elevation data were available from July 2003 onwards and these were used with the stage-storage information from 2002 (Table 3.1) to estimate daily releasevolumes. Prior to July 2003 the releases were estimated by correlating streamflow data from Gage 602B (downstream of Matilija Reservoir) and Gage 604 (North Fork Matilija Creek, and not subject to releases) to identify periods of releases and estimate release rates. These estimates were capped at 150 cubic feet per second (cfs), based on outlet capacity. The resulting releases implemented into the model are plotted in Figure 3.7. (p84)

 

Other Comments:

Gage 604, No Frk Matilija Creek at Matilija Hot Springs

Matilija Hot Springs is located on Matilija Creek below the dam. This gage is actually located less than a mile upstream of the Matilija Creek/NF Matilija Creek confluence under a bridge over Hwy 33. The correct stream gage nomenclature per VCWPD is:

Matilija Creek at Matilija Hot Springs (602) 

North Fork Matilija Creek (604)

Conclusions and Recommendations:

The Draft Groundwater-Surface Water Model of the Ventura River Watershed is a good first draft representation of a complex and dynamic physical system. The disclosure of uncertainties in the modeling process and the errors matching stream flow data suggest that further work is required to create a model that is useful for assessing the various scenarios that have been proposed.

The model must first be able to accurately represent changes in the watershed resulting from the highly variable precipitation during the study period. Robust model performance over a wide range of rainfall and flows is required before an assessment of any future changes can be evaluated.

Because of the inherent error in low flow stream gage data, it is suggested to first calibrate the model to the best available stream flow data for the moderate years and then work to match the high and low flow years. In this manner the physical coefficients may be established to ensure confidence that simulated model scenarios produce useful results.

For example, a climate change scenario would include incremental variations in precipitation and ambient temperature. It is essential that the model can accurately predict the extremes of the recent past before it can project into the future. The current assumptions regarding Arundo donax should be closely examined for ET in Matilija Canyon and effect on streamflow. If the Matilija Dam removal scenario is pursued, close coordination with the Matilija Dam Ecosystem Restoration Project (MDERP) technical team is recommended. The current assumptions for pumping and diversion should be closely examined so that any future water management scenarios may be adequately assessed.

Future development of the model should also include a robust monitoring network including additional stream gages and dedicated monitoring wells to better understand the nature of surface and subsurface flows and provide data to feed back into the model.

References:

State Water Board Instream Flows - Ventura River

Groundwater Dependent Ecosystems and SGMA

.

Is this a Groundwater Dependent Ecosystem?

People enjoy the last of a drying river on Memorial Day,
Ventura River Preserve 5-31-2021 

Flows rapidly dropped through the Ventura River Preserve this year, leaving the riverbed dry by June.  While this can be a common occurrence in dry years, surface flows are directly related to the groundwater below.  Under the State Groundwater Management Act (SGMA), the local Upper Ventura River Groundwater Sustainability Agency (UVRGSA) has been formed to develop a plan to sustainably manage groundwater into the future.  Draft documents have been released in preparation for a Draft Sustainability Plan later this year.

The question of how to determine whether a reach of the river is "connected" to groundwater, and therefore a "Groundwater Dependent Ecosystem" (GDE) under SGMA, is critical to the future sustainability of our water supply.  When a Groundwater Dependent Ecosystem suffers due to groundwater overdraft, the capacity of the landscape to store water can be compromised.    

The following comments were submitted to the UVRGSA regarding this concern.  The technical documents and other references are linked below. 

DATE: 6-18-2021 RE: Early Comments on Draft Supporting Documents for Upper Ventura River Groundwater Sustainability Plan

This memo is a follow up from our conversation regarding development of the Groundwater Sustainability Plan (GSP). The primary concern we discussed is the elimination of large portions of the basin from SGMA oversight through the assumption that surface water is somehow “disconnected” from groundwater. Apart from the fact that there are fundamental flaws in the methodology used to make this determination, the resulting conclusions and management criteria are not consistent with avoiding undesirable results.

The primary Sustainable Management Criteria (SMC) for the UVRGB is the Depletion of Interconnected Surface Water. The analyses presented to date do not adequately assess the groundwater/surface water interactions within and between the different reaches of the basin, or even acknowledge the impact of groundwater pumping on surface flows.

Screening Groundwater Dependent Ecosystems (GDEs)

The Upper Ventura River Groundwater Basin is a shallow alluvial aquifer integral to the riparian floodplain ecosystem of the main stem Ventura River. Throughout these reaches of the river, groundwater and surface water are connected, and to suggest they are not is to undermine the intent of the Sustainable Groundwater Management Act.

Figure 2. Confirming whether an ecosystem is connected to groundwater, TNC

The Riparian Groundwater Dependent Ecosystems Assessment Report characterizes the Robles reach as a “Losing reach with generally disconnected groundwater- surface water.” This categorization eliminates the majority of this Groundwater Dependent Ecosystem from consideration under SGMA by assuming that it is “disconnected” and thus has too great a depth to groundwater to support riparian habitat. Other reaches are similarly dismissed.

Figure 2 from Riparian Groundwater Dependent Ecosystems Assessment

The analysis presented relies heavily on the Nature Conservancy “Natural Communities (NC) Dataset,” using vegetation communities to eliminate GDE polygons from the Upper Ventura River Groundwater Basin. The NC dataset is a statewide geographic computer database that maps vegetation types in all potential GDEs throughout the State of California. The large geographic scope of this map does not accurately represent current on-the- ground conditions, and more robust ground truthing should be undertaken. Even the aerial photos presented tell a different story than is acknowledged in the narrative (i.e. Figure 6 North Robles Habitat Area Photographs, Aquatic GDE Characterization report)

Figure 6 North Robles Habitat Area Photographs

Unfortunately, the UVRGSA analysis does not fully implement the Best Practices for using the NC Dataset guidance provided by the Nature Conservancy, which presents six best practices for using local groundwater data to confirm whether mapped features in the NC dataset are supported by groundwater. (Best Practices for using the NC Dataset, TNC July 2019)

According to this guidance:  

While depth-to-groundwater levels within 30 feet of the land surface are generally accepted as being a proxy for confirming that polygons in the NC dataset are supported by groundwater, it is highly advised that fluctuations in the groundwater regime be characterized to understand the seasonal and interannual groundwater variability in GDEs. (see Best Practice #2.)

one of the key factors to consider when mapping GDEs is to contour depth-to- groundwater in the aquifer that is supporting the ecosystem (see Best Practice #5).

The GIS Spatial Analysis of Maximum Rooting Depth and Groundwater Level presented in the Riparian GDE document does not present such contour depth-to-groundwater mapping or account for temporal variability.

Figures from Best Practices for using the NC Dataset, TNC

Furthermore, TNC guidance acknowledges that;

In many situations, the hydrologic connection of NC dataset polygons will not initially be clearly understood if site-specific groundwater monitoring data are not available. If sufficient data are not available in time for the 2020/2022 plan, The Nature Conservancy strongly advises that questionable polygons from the NC dataset be included in the GSP until data gaps are reconciled in the monitoring network. Erring on the side of caution will help minimize inadvertent impacts to GDEs as a result of groundwater use and management actions during SGMA implementation.

Many of California’s GDEs have adapted to dealing with intermittent periods of water stress, however if these groundwater conditions are prolonged, adverse impacts to GDEs can result.

Therefore, it is likely that the NC vegetation mapping is representative of conditions in which groundwater levels have been frequently and repeatedly pumped beyond the reach of riparian tree roots. Meanwhile, field observations over the past few wetter years show that the riparian vegetation has rebounded, illustrating how the ecosystem responds with the variation in water years. Receding groundwater levels and corresponding loss of surface flows in the current drought will likely reverse this recent trend, with the potential loss of the many young sycamores.

Determining Groundwater/Surface water interactions

TNC guidance for determining GDEs recognizes the importance of surface flows;

In addition, SGMA requires that significant and undesirable adverse impacts to beneficial users of surface water be avoided. Beneficial users of surface water include environmental users such as plants or animals, which therefore must be considered when developing minimum thresholds for depletions of interconnected surface water.

The Model Results and SMC Implications Presentation (March 25, 2021) reaches the conclusion that:

• Basin water budget is dominated by streamflow percolation into the Basin and groundwater discharge to Ventura River
• GW pumping averages only ~10% of the GW Budget As low as 4% in wet years 
Up to 31% in dry years
• Basin GW levels will be lower in dry seasons, but Basin will still re-fill in normal to wet years

The conclusion that there is no impact from pumping based on the fact that the basin rapidly refills in the wet season points to the likelihood that the surface water is in fact “connected” to groundwater during these periods. Moreover, the fact that pumping represents up to 31% of the budget in the critical dry years raises many questions.

figure from Model Results and SMC Implications Presentation (March 25, 2021)

The Model Results identify four areas of concentrated pumping, three of which directly impact groundwater levels in the “Robles Reach.” This reach is the area with the most storage in the basin, and should be considered as the “primary sub-basin” for water supply. Pumping in this reach directly affects conditions throughout the basin.

The analyses and graphs presented in the Model Results do not provide information on the spacial and temporal surface flow conditions as they relate to groundwater levels. Because the downstream reaches are largely dependent on surface and groundwater flows out of this sub-basin, further analysis is needed to more clearly define the relationship between groundwater levels and surface flows. The analyses should, at a minimum, determine threshold groundwater levels at which surface flows are diminished or eliminated, both in the reach being monitored and downstream.

Groundwater/Surface water interactions
Conjunctive Use Study 1978 

This relationship was established decades ago in the Ventura River Conjunctive Use Report (1978) which states that;

Flows in the live stretch are affected by both the rate of recharge of the upper part of the Ventura River groundwater basin and by the rate of groundwater extraction from wells in the river.

Investigations published in the Conjunctive Use Report identified groundwater elevation thresholds in the upper basin at which flows in the live reach will cease;

when the water level in well 4N23Wl6C4 falls below Elevation 495, surface flow in much of the live stretch stops although some pools remain. A flow of 1 cfs or more in the live stretch corresponds with a water level in this well of greater than about Elevation 507.

Groundwater levels also affect surface flows in the Robles Reach, which frequently dries up despite constant inflows. Unfortunately, the Aquatic GDE Impact Analysis is quick to dismiss the effect of groundwater elevation on surface flows;

No monitoring is recommended at either of the critical riffle aquatic GDEs or the Robles Habitat Area, as impacts from pumping in these areas were determined to be minimal or non-existent.

This conclusion is inconsistent with the guidance provided in Monitoring Networks and Identification of Data Gaps BMP (DWR 2016) which states:

23 CCR §354.34(c))(6): Depletions of Interconnected Surface Water.

Monitor surface water and groundwater, where interconnected surface water conditions exist, to characterize the spatial and temporal exchanges between surface water and groundwater, and to calibrate and apply the tools and methods necessary to calculate depletions of surface water caused by groundwater extractions. The monitoring network shall be able to characterize the following:

(A) Flow conditions including surface water discharge, surface water head, and baseflow contribution.

(B) Identifying the approximate date and location where ephemeral or intermittent flowing streams and rivers cease to flow, if applicable.


(C) Temporal change in conditions due to variations in stream discharge and regional groundwater extraction.

(D) Other factors that may be necessary to identify adverse impacts on beneficial uses of the surface water.

DWR guidance provides detailed information on developing a monitoring network to accurately assess these concerns.

Establishing Minimum Flow Thresholds

As described above, the current GSP analysis incorrectly concludes that groundwater pumping has little to no effect on surface flows throughout the majority of the basin. But even for the identified groundwater dependent “Habitat Areas,” the development of minimum flow thresholds is inadequate. For example;

For the Foster Park Habitat Area, while the City’s low-flow thresholds are based on only one HSI score evaluated in the Padre study (average thalweg depth), we understand this currently provides the best available information to establish minimum thresholds for the depletion of interconnected surface water sustainability criteria.

This statement ignores best available science, including the recently published CDFW Draft Instream Flow Recommendations (2021) as well as the NMFS Draft Biological Opinion for Foster Park Wellfield (2005).

Implications for the UVR Groundwater Sustainability Plan

According to the Brownstein Water Group, the Cuyama Valley Basin and the Paso Robles Area Subbasin GSPs were recently deemed incomplete for deficiencies in their definitions of sustainable management criteria (SMC), including minimum thresholds and undesirable results. Some of the concerns cited by DWR are that the GSP;

• provides insufficient detail for how it determined that the selected minimum thresholds . . . are consistent with avoiding undesirable results
• does not relate different minimum thresholds for different portions of the basin to conditions that could cause undesirable results
• does not sufficiently discuss expected impacts and therefore “precludes meaningful disclosure to, and participation by, interested parties and residents in the Basin.

It is clear from these recent DWR determinations that much more work is needed to develop and present a clear understanding of the workings of the Upper Ventura River Groundwater Basin, the potential impacts from groundwater pumping, and a plan to better manage the limited resource to ensure future sustainability and a healthy ecosystem.

Recommendation:

These initial comments are provided as requested, in good faith, prior to the release of the Draft GSP in the interest of stakeholder engagement and with the hopes that the UVRGSA is able to augment the current analysis and develop a meaningful assessment of the impact of groundwater pumping on surface flows in the Ventura River. It is clear that this will be necessary to successfully develop the Groundwater Sustainability Plan to a level that satisfies the objectives of the Sustainable Groundwater Management Act (SGMA) in order to gain the support of local stakeholders and approval by the California Department of Water Resources.

References:

Upper Ventura River Groundwater Sustainability Agency (UVRGSA) 

• Model Results and SMC Implications Presentation (March 25, 2021)
• Riparian Groundwater Dependent Ecosystems Assessment Memorandum, UVRGSA, April 2021
• Aquatic Groundwater Dependent Ecosystems Assessment Memorandum, UVRGSA, April 2021

Mapping Indicators of GDEs, Groundwater Resource Hub, The Nature Conservancy

IDENTIFYING GDEs UNDER SGMA; Best Practices for using the NC Dataset, The Nature Conservancy, July 2019

Monitoring Networks and Identification of Data Gaps BMP , CA Dept of Water Resources, water.ca.gov

DRAFT ENVIRONMENTAL IMPACT REPORT, VENTURA RIVER CONJUNCTIVE USE AGREEMENT,  Report on the Environmental Impacts of the Proposed Agreement Between Casitas Municipal Water District and the City of-San Buenaventura for Conjunctive Use of the VENTURA RIVER - CASITAS RESERVOIR SYSTEM, Prepared for CMWD and the City,  June 1978

GSAs Shooting 50% on GSPs—DWR Releases First GSP Assessment Results for High Priority Basins, Brownstein Water Group, June 4, 2021

More info:

Sustainable Groundwater Management Act (SGMA), California Department of Water Resources

Groundwater Resource Hub, The Nature Conservancy

Natural Communities Commonly Associated with Groundwater, California Department of Water Resources

Groundwater Dependent Ecosystems - How can we manage groundwater to benefit both people and nature? The Nature Conservancy, scienceforconservation.org

On this blog:

Understanding CDFW Instream Flow Recommendations

Comments on CDFW Instream Flow Recommendations

 Via E-mail to InstreamFlow@wildlife.ca.gov

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 https://www.venturariver.org/2021/04/understanding-cdfw-instream-flow.html

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 California, understanding 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.”

Recommendations

• 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.

Sincerely

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.”

   Op-Ed by Alasdair Coyne and Paul Jenkin: Ventura River flows will shape our communities, Ojai Valley News, 12 March, 2021

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. 

   Bert Rapp's Op-Ed: Good science will produce proper flow recommendations, Ojai Valley News, 19 March 2021

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). 

   River-flow report stirs controversy: Response deadline extended , Ojai Valley News, 09 April 2021

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.

More:

ShiftingBaselines.org

Retrospective on the Thomas Fire

The Ventura River has demonstrated amazing resiliency following the Thomas Fire.  The river appears healthier now than it has been in decades following the influx of sediment eroded from the mountains.  However, the initial flushes following the fire negatively impacted the river until the storms of 2019 "rolled" the bottom breaking up an impervious layer formed by ash and silt deposits.  The photos here are provided to illustrate what this looked like in the summer of 2018.

Ventura River, May 2020

Ventura River following the Thomas Fire, January 2018

 

Ventura River following the Thomas Fire, March 2018

The first storm immediately following the fire in January 2018 moved large amounts of black ash and very fine organic matter off the burnt hillsides. The second storm in March eroded additional fine sediments with a brown soil color.  These two events combined to form a hard crust on the stream bed.

The photos below from June 1, 2018 describe observations of this phenomenon. 

Ventura River 6-1-2018

The river bottom was embedded with ash and fine sediment that filled the voids and effectively "cemented" the cobble and gravel.  In the image above, a cobble was removed by hand to expose the layers below.  With no tools handy, it took considerable effort to loosen and remove this rock.

Ventura River 6-1-2018

Once a rock was removed, the hard crust could be broken up and pulled away by hand, further exposing the riverbed.  Here the substrate was agitated to allow the river flow to transport the fine sediments away.  The dark color of this plume indicates the organic ash eroded from the hillsides in the initial rain event.

Ventura River 6-1-2018

Removing a couple more rocks and agitating the surface eventually cleared this small area of river bottom.  The brown crust can be seen adhered to the rocks.  The image below provides an overview of the site.

Ventura River 6-1-2018

The upper Ventura River groundwater basin relies on flows infiltrating through the alluvium in the river reach downstream of the Robles Diversion.  The graphs below are from the monthly water update provided to customers of the Ventura River Water District.  This water district relies on wells in the Ventura River in the general vicinity of the photos above.  As noted at the time, groundwater levels did not  recover as normally expected in 2018.  However, the 2019 storms resulted in river flows that adequately cleaned out the river channel to allow recovered infiltration as illustrated by the 44 foot rise in groundwater in the bottom chart.  

Ventura River Water District, July 2018

Ventura River Water District, June 2019

On this blog:

Thomas Fire

Post fire storm event, Jan 9 2018

Matilija Dam - water quality

March Rains - fires, flood, drought, and sand

March rains