One of the major issues currently facing the Ventura River is 'pumping and diversion'. The river has been listed by the State Water Resources Control Board as 'impaired' in Reaches 3 and 4 due to excessive water diversion. The water board is now considering developing a TMDL, or 'Total Maximum Daily Load', for this impairment. The alternative is a MOA (Memorandum of Agreement) and plan of action for local water agencies to cooperate on a groundwater management plan.
Diversion of surface flows occurs at the Robles Diversion Dam (Reach 4) and at Foster Park (Reach 3) as well as smaller private diversions. Pumping occurs at numerous wells that extract water from the shallow aquifers that are connected to surface flows. In both cases, the amount of water flowing in the river is diminished, impairing ecological function. For example, low flows become a problem when combined with excessive algae growth - this reduces dissolved oxygen levels that aquatic life depends upon. (See Algae: problem or symptom?)
Pumping water from wells during dry summer months may cause pools to rapidly dry up, stranding and killing native steelhead trout and other aquatic species. Although this often goes unseen (they become fodder for predators such as herons, racoons, etc.), fisheries managers in past years have responded by relocated fish from drying pools.
Pumping and Diversion has been discussed during several of the recent watershed council meetings, along with presentations about water rights and the effects of wells on surface flows. As one would expect, there is controversy surrounding the cause and effect, and some even question if there is reason for the impairment listing.
In order to illustrate the problem, Santa Barbara ChannelKeeper produced this video:
The timelapse sequence in this video and the pressure logger illustrate the rapid filling and drying of a pool on the Ventura River Preserve. Because this occurs independently of time of day it suggests that something other than natural evapotranspiration is occurring to impact surface flows in the river.
To illustrate the issue, local groundwater professional Jordan Kear has provided presentations to the Watershed Council. These graphics are from Surface & Groundwater Interaction Study, Kear 7-17-12
The main stem of the Ventura River is divided into two groundwater basins, with the division occurring at Foster Park.
To understand what happens to surface flow, one must understand how the stream interacts with groundwater. A stream may be 'gaining' or 'losing' depending upon the level of the water table beneath and adjacent to the river channel. And when the water table drops far enough the stream becomes 'disconnected.'
One of the areas in question is Reach 4, the section of river downstream of the Robles Diversion within the upper Ventura River groundwater basin. As the figure below illustrates, this 'Robles Reach' is usually a 'losing stream,' which often becomes 'disconnected' in dry periods.
Then, as river flows increase during winter months and the groundwater basin fills back up, and surface flows re-establish. (In extremely wet periods it may also become a 'gaining stream')
|Surface water (dotted line) and Groundwater (solid blue line) interaction|
in the Robles Reach of the Ventura River (Kear Groundwater)
Although this Surface & Groundwater Interaction Study concluded that "pumping of wells has a relatively minor effect on river flow," this was based upon an experiment that revealed the Meiners Oaks Water District wells reduced river flows by up to 1.5 cfs (cubic feet per second.) However, this conclusion does not take into account the cumulative effects of multiple wells pumping from the same groundwater basin when summer inflows from Matilija Creek may only be 5-10 cfs or less.
|Reach 4 - Wells within 1000 ft of Ventura River|
What this study does demonstrate is that there is some direct interaction between groundwater pumping and surface flows. What is less clear is the effect from wells farther from the river, but within the larger Upper Ventura River groundwater basin.
|Wells within the Upper and Lower Ventura groundwater basins|
Last year, a first cut at developing a water budget for the two groundwater basins was presented with the Upper and Lower Ventura River Basin Groundwater Budget. (The first draft of this analysis suggested an overdraft of 3,240 acre-feet per year, before Lake Casitas storage/supply was added.)
Reach 3 is under similar stress, as the City of Ventura has recently constructed new wells at Foster Park. Although these wells are regulated by NOAA Fisheries, who have established minimum flow criteria, this reach is influenced by other extractions which have cumulative effects on surface flows.
Although this is clearly a difficult issue, the TMDL listing has brought many of the major water suppliers and users together to potentially work cooperatively on a groundwater management plan.
It is important to understand that this is not only about endangered species and recreation, which are protected under the Clean Water Act, but most importantly the future sustainability of our communities, including over 100,000 residents in Ojai and Ventura:
- Our communities depend almost entirely on the Ventura River for water supply
- In recent years, expansion of agriculture as well as planned urban development are increasing pressure on this limited resource
- New wells are being constructed, increasing groundwater pumping
- Currently there is no coordinated oversight of groundwater resources on the main stem of the Ventura River
- We are clearly at, or above, the maximum sustainable water extraction from the Ventura River
Pumping and Diversion Fact Sheet
A Really Short Course on Water Rights, Birosik 6-13-12
Surface & Groundwater Interaction Study, Kear 7-17-12 (2.8 Mb)
Upper and Lower VRB GW Budget and Management Presentation 05-25-2010 (3.4 Mb)
Upper and Lower Ventura River Basin Groundwater Budget and Management Plan (18 Mb)