it. Okay thank you. So as I mentioned this talk is Surface and Groundwater Interaction in the Southwest Ojai Basin. Tonight's meeting of course as I was introduced Jordan Care PG stands for Professional Geologist CHG stands for Certified Hydrogeologist and I've had the pleasure of working in Ojai for the better part of 20 years now Starting with minor work for a number of small farmers and residences, but really picking up steam when I worked on my Master of Science thesis conducting a number of aquifer tests and stratigraphic analysis of the basin for the Ojai Basin Groundwater Management Agency.
And which is now inclusive in the groundwater sustainability agency for the OI Basin and I'm happy to serve as agency hydrogeologist among hundreds of other projects we work on at CARE Groundwater. This image gives a really brief, simple picture of the basin and its position in the watershed. The blue outline is the San Antonio Creek Watershed. The light blues are surface waters.
The black line in bold is the agency jurisdiction for the Ojai Basin GMA. And the red line is more or less the basin boundaries, although that's been modified since this graphic was prepared. Within this are also some of the purveyors, the city of Ojai area and the purplish and the Thacher areas being which are Served by various purveyors, Hermitage Mutual Water Company, Senior Canyon Mutual Water Company, Ridley Road, Siente Robles and of course the Golden State Water Company shown in this graph. That's now the Casitas Ojai system.
Way back once upon a time the basin was thought of as a little bit of a sandbox right on top of a bunch of bedrock that QT that's sort of been in orange there represents What was thought of in 1933 as what we now know is the OI Basin. Come 1953, we get a bit better idea about what's going on in the basin. Number of wells had been drilled to depth in the basin area and still we're looking at just a sandbox over undifferentiated tertiary bedrock formations.
Come 1992, we get few more e-logs that are representative of what's going on in the basin, number of wells with more detailed lithology and a better handle on how the water levels have changed over time. And what that effective base of freshwater which is not necessarily the base of the alluvium in the basin was begun to be defined. Come 2005 we have many more e-logs at our disposal and were able to correlate these objectively across the basin. In this particular case Generated the green to represent clay aquitards, whereas the white in this case were where the aquifers and the reddish material was. The bedrock at the bottom of the barrel if you will.
Based on the testing that we did in the early some 20 years ago early knots, we found that really the most productive areas of the basin are in the central and eastern portion of the Ojai Basin The production tends to be a lot less from wells that are drilled in that area. Although the aquifers do correlate at depth, it's that deep production system that is yielding the water to the cities and the agricultural interests within the basin.
And over on the west side things are a lot more clayey there's a lot more fine grain material Water moves a lot more slowly through those zones, and there tends to be what's known as this perched aquifer system. And that's the one that seems to have the most weight with respect to the surface and groundwater interaction. More detailed model development went in in more recent years really stratifying the basin with respect to quantification of different characteristics of aquifers, how permeable and porous they were, and correlating them across the basin But if we take a look at what happens to a drop of water as it enters the basin as surface water, we take a little bit of a tour from northeast to southwest in the basin. And in this case, the flow into the Ojai Basin from San Antonio Creek as it has a confluence with Gridley and Ladera Creeks to become San Antonio Creek proper.
In this case, this is Ladera Road crossing creeks flowing over took this picture right about the location of that yellow star in the inset map. As we go a little bit further downstream, it gets a bit more picturesque and you see quite a bit of water flowing through the old diversion works for the San Antonio Creek Spreading Grounds. As we get deeper into the basin, Fort Ice Road is projected here and you can see the flow's a lot less. This was all taken on the same day a couple years back but by the time we get to where that yellow star is, the water has fully infiltrated into the basin Now it flows in the subsurface here toward the deepest aquifers or those production aquifers that are in the central portion of the basin.
As we get further downstream, the water begins to daylight again, in this case south of Grand Avenue Bridge. Again these are all on the same day and then as you get further south, the flow picks up a bit more and finds its way out of the basin. And by the time you get south of the O Avenue bridge on this particular day, it's flowing Quite a bit of algae in the water. This is a May photograph, and all these were taken on the same day.
So if we think about what's happening in the bigger picture back to that original graphic, we see surface water flowing into the basin, finding its way into the subsurface in one way or another, and then discharging out near the boundaries of the Ojai Basin GMA. That southern boundary is where the Arroyo Parida Santa Ana Fault lifts up bedrock on the south side and allows surface water and groundwater to come up against that boundary, and jump up over that dam if you will. A natural feature that keeps flow in the San Antonio Creek effectively perennial at that point always flowing but it takes about 12 inches of rain on the valley floor before we see that surface water flow crossing the basin. You may have seen a little bit surface flow this year when we had some of those flashier storms.
But to get a sustained flow, we typically need about 12 inches of rain and that's about half of the average over the long term in the Ojai Basin. This year we've got just under four inches of rain on the valley floor at the county fire station up on the ridge tops it might be closer to six inches and that's pretty typical that we see close to double the amount of precipitation at elevation which is where much of the recharge comes from as opposed to on the valley floor, slightly drier.
Now where that first water goes, the OBGMA has a network of monitoring wells and this is downloaded today from one of those monitoring wells at the San Antonio Creek Spreading Grounds Rehabilitation Project. This is from a 210 foot deep well that's screened from 190 to 210 feet and this is a question we often get. We get an inch of rain how much does that contribute to the basin? And this is the answer And that December 28th to 31 storm brought about 1.42 inches of rain on the valley floor, and we see a jump up a couple of weeks later from about 55 to 62 feet. So we had about seven feet of rise in groundwater at this point. This is where the water first reaches the saturated alluvium of the basin along San Antonio Creek.
That January 24th to 30th storm system that we had Had about two and a half inches of rainfall on the valley floor. And you can see again, a couple of weeks later that bigger spike bringing up nearly nine feet of increase in water level. And this is always fun to look at in the beginning of the water year because it's been drier and the consecutive storms are not blended into noise. So when you look at a graph like this, it's somewhat easier to see how The level on the right hand side of the y-axis of this graph jumps up with that precipitation.
Now, we have several of these wells in which we monitor relatively consistently and there in the triangle is the point of discharge from the basin. Now we have one of our key wells it's known as the Elrod well and we have a logger in there that monitors the depth to water and the temperature of the water At 90 minute intervals. So from 2017 to 2021, you see it here except the times when those aberrative data points are present. The logger had to be removed because the pump was being worked on. It isn't active producing well but you can see how the precipitation in wetter years makes a significant increase in groundwater levels and storage over the course of each year and it recedes Typically from the late spring to the wintertime before the next storm systems come along.
But you can see the big jumps here in 2019 and really sustaining that in 2020, down where we are in 2021, we're just near the point where we're at what we call the nadir, a low point of storage in the basin but then also starting to see some recovery on the longer term scale from 1944 to 2024, shown here on this graph. We use this to create a long-term hydrograph what years and years of precipitation and drought how those are recorded in the basin water levels.
And just jumping forth to today's system we're at 143.04 feet below ground surface at that key well area. And that's about 73% of the basin capacity or 58,400 acre feet You heard it here first. Now, that's what's going on in the producing aquifers of the basin. But if we look around this city, we notice that there are several places where water is very shallow.
There are places where we need to pump off groundwater French drains around foundations and walls and retaining systems and things like that. But we also have a network of monitoring wells from environmental investigations places where there were leaking underground storage tanks, typically in some cases of dry cleaners. But that's resulted in a number of field points here shown in this map as these light pink dots and there's one right there in the south portion of the city right along Grand Ohio Avenue you have I think that's Gabriel's and then you've got a couple of other old or new gas stations that had leaky underground tanks and a number of monitoring wells were drilled there. And what we noticed is that the data from those wells, they're all very shallow some 25 or 30 feet.
They all encountered groundwater very shallowly some three 10 or 13 feet and it tends to stay relatively constant right there. So why is it that we have this shallow water in the area of the city? And this deep water that fluctuates seasonally and with production in the production aquifers of the basin. And the answer is that we have this perched aquifer system, water that precipitates within the city and on the west side of the basin tends to go to that perch system first and then discharge to San Antonio Creek whereas the water that infiltrates within San Antonio Creek and Thatcher Creek and Horn Creek and Reeves Creek on the east end and the north end They tend to find their way into the production aquifers, and that's separate. And why that's important is because of where it comes out.
The first daylighting water in San Antonio Creek today tends to be right around Soule Park Golf Course. It's something that we've been mapping. You can see the GPS unit here over time for years now. And the idea is to monitor where that daylighting occurs on a monthly basis and get a snapshot of where it's flowing in, because that tends to be relatively consistent. Consistent regardless of the depth to water in the producing aquifers.
So we also measure the flow at the points of exit. This is today's photo underneath Creek Road where the surface water discharge is from underneath much of the city area. The creek is known as Stewart Ojai Creek Montgomery or Fox, depending on what maps you look at. And this is the discharge that we see coming out of that little notch today under Creek Road.
Now on San Antonio Creek proper just stones throw away literally from that notch is where we monitor the outflow from the basin because it's direct surface water flow directly over bedrock. This is today's photograph so this is a... You can see how beautiful it was. The trees are deciduous and but yet the creek is flowing And we measure this by taking a flow probe in sections of the creek right here.
All of this flow that you see was gaining from the point of that first daylighting groundwater where that GPS unit was in the middle of the creek, and at the same time, the depth to water in the keywell area is over 140 feet down. So we take these monthly readings, and we've been doing this since 2019 in San Antonio Creek at a monthly basis. And we also have added when there is flow there, flow out of Montgomery Creek in that notch.
And today's flow was about just under six tenths of CFS from San Antonio Creek proper and about five, you know that'll be one hundredths of a CFS out of the Montgomery Creek notch. That adds up to about 0.64 CFS, which is close to 300 gallons per minute. So that water you can imagine flowing continuously adds up. These are snapshot-based data points and they tend to be pretty effective but we see that between 30 and 45 acre feet per month discharges to San Antonio Creek from the Ojai Basin during this time frame And in the water year to date, we have over 180 acre feet that has flowed out of the basin.
So what does this mean in some of these scientific terms? This is a graph that we've developed to illustrate this and I'll explain it here. The upper graph is daily rainfall. So every time it rains a little bit, we put a little bar on this graph and you can see how the rain was much more intense in 2017 higher precipitation in total, but 2018 19 and 20 similar events.
Potentially more dense in 2019 a little less dense in 2020. But as we go down in this graph, this is a pretty complex graph so bear with me on the on the X axis of all of this is 2017 18 1920 and now 21. On the Y axis of the center graph is the elevation of the water That is at ground surface at the key well, but 880 feet. The ground surface elevation at the spill point of the Ohio Basin on San Antonio Creek just under 640 feet there and then on the right Y axis is the discharge rate of flow that is how much water is flowing out? That's in the pink for San Antonio Creek in total near where it's confluence with the Ventura River is and then And those little magenta Xs are the flows that we've been measuring on a monthly basis.
On the darker blue is the depth water or elevation in that key well, the automated logger that records it and then the elevation of the spill point of water daylighting water is the lighter blue. So where that light blue is continuously vertical, that's when San Antonio Creek is continuously flowing across the basin And the lighter pink material, or the pink bars are where the discharge is measured by the county at Creek Road. So that is what the county is measuring as entering the upper Ventura River groundwater basin near its confluence with the Ventura River. Now I happen to check today you'll see that there's no real pink bars much past the end of the 2020 water year Much of that flow has been underground in San Antonio Creek. It doesn't daylight at that point because it's infiltrated out of the Ojai Basin, over that bedrock notch and into a number of wells, little surface diversions and quite a bit of uptake from plants and trees in that area.
So more water is flowing out of the Ojai Basin as surface water than is flowing into the upper Ventura River basin as surface water. And I happen to check today at about the same time that we were collecting this measurement today of 0.64 CFS, cumulatively coming out of the Ojai Basin and at the Ventura River in at the Casitas Vista Bridge where the United States Geological Survey measures the flow continuously there They were measuring about 1.5 CFS, so less than half of the flow that is coming out of Ojai is what is measured in the Ventura River.
And there's quite a bit of alluvium that has subsurficial flow there as well. So the idea is that we have a significant amount of flow coming out of Ojai but nothing compared to what Actually flowing in the Ventura River. It's a very small component that is finding its way out of the Ojai Basin, out of the perch system and into the Ventura River system. And this is important because if we look at what the Ojai Basin is and where the city is it's largely over the perched aquifer system. That's water that flows into the city area finds its way out of San Antonio Creek separately and distinctly from deep production zones, and this is shown in this cross section here.
So the idea is that what we can do to affect the water systems near surface within the city can have a greater and more acute effect on flow in San Antonio Creek for habitat benefits or water retention projects acting in the city area. It's the places like the San Antonio Creek spreading grounds That can focus on what's going on to provide the production aquifers that are located at depth within the city. And part of the projects that I believe Ms. Hirsch will be talking about and these, the depth discrete monitoring well which actually is shown here later agenda items will help to better quantify and identify exactly what is going on quality and quantity wise over the long term within this portion of the city and help both Contribute to the design of and realize the benefits of many of the projects that the Wildlife Conservation Board, Ventura River In-Stream Flow projects and grant funding are geared toward.
So it's a pretty complex story. I thank you for your attention and happy to take any questions if there probably are many but we'll be around for many of the other agenda items as well so I thank you for your attention and appreciate the ideas. I see a hand raised or three.
