Updated 19th February 1999; 6th May, 16th October 2001; 5th November 2005; 15th May, 15th June 2006; 27th October 2007; 1st October, 8th, 19th, 30th November 2008; 6th May, 2nd, 18th November 2009; 26th June 2010; 6th January, 27th May, 5th October 2011; 22nd August 2012; 15th, 16th September 2013
The cave is a major resurgence for the area and a large diameter pipe removes
water supplying Santander. Information gleaned from the Dirección
General de Obras Hidráulicas y Ciclo Integral del Agua in 2005
shows an average water flow from the resurgence over the previous 20 or so
years of 951 litres per second. (The Matienzo / Riaño water resurgence
at Los Boyones emits 650 litres per second on average. Unlike the 4 Valleys
System, there is only one known feeder or cave which drains to the Nacimiento
An optical brightener test from the end of the Sumidero de Cobadal over Easter 2006 gave a positive result after 5 - 7 days during medium to medium-high flow. During the 6 or so visits over a fortnight the water levels were slow to react after some heavy rain, and even then only rose by approx. 7cm. Los Boyones rose by 120cm much more rapidly. The details of the test are found here. There is a possiblity that water from the Sumidero might drain to Torca La Vaca during low to normal flow, only passing over into Fuente Aguanaz during high stage. Some suggestions regarding water sources for Aguanaz are detailed here. In 2009 these possibilities were outdated when an inlet, apparently from La Gatuna, was explored.
The resurgence can emit large quantities of water, flooding the low lying ground around Entrambasaguas and beyond. One effect of the Whit 2008 flood was to jam leaves around the door of the new pumping station, which is probably 7m above the normal water level. A smaller flood in October of the same year was shown on national TVE news. (Photos here).
After a very dry summer, the Diario Montañés (22/8/2012) reported a flow of 0.1 cumecs.
The resurgence area has an outdoor interpretation centre with 4 boards explaining about water and the environment. Further boards are in the old pump houses.
The water level at the bottom entrance is at about 55m altitude and is reached by walking down concrete steps. Sixty metres up behind this - reached by a track setting off on the right of the car park - is a hole below a scar in a depression which is where the pipe reaches to abstract the water. The entrance for cavers is another 70m south and starts as a route between boulders. The grid reference for this entrance was altered in 2008 and is that shown in the heading. Just below the top of the rope climb, a hole was opened up in 2009, heading west. This turned out to be an alternative way down to the stream rather than any high level development.
The site is mainly swimming. Half way through, the water can be left and there is an inlet on the western side. This was pushed and resurveyed in the summer, 2009. Beyond the aven the inlet stream continues through an choke to two short ducks and a continuing stream passage which lowers to a flat out crawl with a slight draught. Before this, a climb out enters a large chamber / passage which may continue south beyond an unexplored pitch down. The area was reinvestigated and pushed on one trip at Easter 2010. "Had a good look round in the boulder choke. Could not find the main way on but found plenty of high level passage with deep holes in the floor. Possible ways on? About 250m unsurveyed?" About 150m were surveyed to 40m above the stream where the high level passage lies. See photos taken on this trip.
An inlet on the east was also explored, summer 2009, for 70m and ending at a too tight rift with no draught. A aven was free climbed 9m after a tight squeeze up to where it continued up out of sight.
The streamway up to sump 1 was re-explored in the summer 2013 and all side passages at water level were found to be undercuts or blind air bells. The line was also repaired.
The southern sump was dived at Whit 1995 and was passed in 5 to 6m visibility, after 35m, at a maximum 5m depth to a large sump pool on the other side. De- kitting occurs on a mud and boulder bank on the left. The continuation was then fully explored for 500m during the summer of that year and consisted of swimming and wading until the passage climbs several cascades to meet the unexpected sump 2.
The 25m long sump 2 was passed to approximately 300m of passage, ending at a boulder choke with a slight draught and one potential digging site. An extremely small, sharp sump continues at stream level. This was entered at Easter 2001 to an airbell to the right of the sump and then pushed in the summer to a "quite tight close down", 5m from the previous limit. Running water could be heard from the rockfall above. At Easter 2006, this seems to have been dived again.
There is a climb above sump 2 which needs attacking.
"The inlet on the left" after the second sump was pushed at Easter 2001. The passage continues tight through a few short climbs. A small chamber leads to a larger one with mud and boulder walls. A stream enters through the ceiling. The place smells of "outside".
Compared to Torca La Vaca, about 1.5km to the east, Fuente Aguanaz is a disappointment. There would appear to be no reason why this cave should not have (a number of) high levels. Perhaps the western extensions in 2009 have started to reveal these. More climbing up from the stream level and investigating avens is required.
There was apparently no account of the upstream passage from the middle entrance being explored until the summer 2013. Some photos were taken near the downstream end; more photos have now been taken and the passage surveyed.
A small hole on the east bank of the resurgence is the entrance to Invisible Cave, site 3283, a stream passage apparently not connected to Fuente Aguanaz but probably connected in the past as an inlet, before Fuente Aguanaz entrance cut back. A small, 4m long cave in a gully above the Aguanaz cavers' entrance was maypoled into in summer, 2009.
A diagram of the hydrology of the San Antonio - Hornedo - Cobadal area drawn after Easter 2011 can be found here.
Over three days in July 2011, the supposed upstream course of Fuente Aguanaz (or, at least, part of it) was dowsed. The furthest point reached was a small sink close to the entrance of the Sumidero de Cobadal. A number of inlets and sinks were also highlighted. See the links below.
References: Cawthorne R, 1987; anon., 1988 (logbook); material
in file; anon., 1989 (logbook); Davis J and Corrin J, 1989; Corrin J, 1990;
Corrin J, 1992b (survey); Corrin J, 1994b (survey); anon., 1995b (Whit logbook);
anon., 1995c (logbook); Corrin Juan, 1995a (survey); Corrin Juan,
1996 (survey); García José León, 1997 (survey);
Corrin Juan, 1997c; anon., 2001a (Easter logbook); anon., 2001c (Summer logbook);
Corrin Juan, 2003a; Corrin Juan, 2003c; anon., 2005c (autumn logbook); Corrin
Juan, 2006a; anon., 2006b (Easter logbook); Corrin Juan, 2007; Corrin Juan
and Smith Peter, 2007; anon., 2008e (summer logbook); anon., 2008f (autumn
logbook); anon., 2009a (Easter logbook); anon., 2009b (Whit logbook); Corrin Juan, 2010; anon., 2010b (Easter logbook); León García José, 2010 (survey); Corrin Juan, 2011; anon., 2011d (summer logbook); anon., 2013d (summer logbook)
Entrance pictures : middle entrance batch 1 : batch 2 : top entrance : bottom entrance
Underground picture(s): yes : optical brightener test 2006 : fossils 2009 : upstream from the middle entrance 2009 : western inlet extensions Easter 2010
upstream and downstream from the middle entrance 2013
Video: Resurgence and information boards : Exchanging cotton wool detectors during an OBA test : Upstream of resurgence and middle entrance (YouTube) : moderate flood at San Antonio (YouTube)
Detailed Survey : 1:1000 (notes from 2009, 2010 to be drawn up) : passage upstream of the resurgence, 2013
Line Survey : on whole area survey (very small at northwest corner)
On area survey : Survex 3d file showing Hornedo and San Antonio areas (summer 2013)
Dowsing reactions close to this cave : All dowsing reactions in the supposed Fuente Aguanaz catchment. (Article about the dowsing carried out in July 2011 can be found here.) : beneath a 3D landscape (Therion file, January 2012)
Survex file : yes (summer 2013)
Passage direction rose diagram (Patrick Warren): yes