To determine the spring fed by the stream in the Sumidero de Cobadal (Entrambasaguas)

Methods, Timings & Results

La Expedición Espeleológica a Matienzo, abril 2006

Juan Corrin

   This document records the methods used and results obtained to trace the water flowing from the end of the cave system Sumidero de Cobadal to possible springs at Fuente Aguanaz, Los Boyones and a river-side spring at Arronte. Background information for this project is to be found in Proyecto: Determinación de la Fuente alimentada por el río de El Sumidero de Cobadal (Entrambasaguas), previously circulated.

   2.1kg of dissolved Tinopal CBS-X optical brightening agent (OBA) was poured into the underground stream at Cobadal. Cotton wool detectors at Fuente Aguanaz, Los Boyones and Arronte were used to absorb the agent. Qualitative detection was by fluorescence under UV light. A positive result was achieved at Fuente Aguanaz between 5 to 7 days, proving that water from the downstream end of the Sumidero de Cobadal flows underground to emerge at the rising of Fuente Aguanaz, a straight line distance to Fuente Aguanaz of approximately 4.9km.

   Optical brightening agents are widely used as water tracing chemicals due to non-toxicity, strong absorption on cotton wool, ease of detection under UV light where it glows blue, and lack of colouration to water. Tinopal CBS-X OBA was ideal for use in this project as all three possible resurgences were public water supplies.
   The detectors were left in the resurgence water for up to 7 days where they absorbed the OBA. Immersion for longer than this may have masked the fluorescence with other contaminants. A check for background fluorescence involved checking detectors every couple of days for 4 days before any OBA was added to the water in Cobadal.
   The people who handled the OBA took precautions when handling the detectors, e.g. wearing gloves. OBA dust was kept to a minimum with thorough washing and checking of hands and clothes with the UV lamp. It was found that once the OBA was absorbed onto the skin, it neither washed out, nor was absorbed onto cotton wool.
   The time required for the project was over three weeks from background testing to final removal of detectors. Moderately low water flow to moderately high water flow conditions were observed throughout the test. Too little water may not have carried the OBA quickly enough, and flood conditions would have put the OBA into high level pools which would then re-contaminate the water in a future flood.

Further information
The following documents can be found as pdf files
The original proposal document -
- Proyecto: Determinación de la Fuente alimentada por el río de El Sumidero de Cobadal (Entrambasaguas)
- Technical details for Clariant Leucophor
- Details of Dye Testing in Chapel-le-Dale

Equipment, methods and timings
UV lamp A combined torch and UV lamp for detecting forged banknotes was obtained from Maplins. ( Ultraviolet mini lantern, code ZC10L, price £9.99). This proved ideal throughout all the tests, producing little visible light to confuse the test.

Detectors Cotton wool BP was cut into rectangles approximately 15 x 10cm and held inside 2 layers of chicken wire. Synthetic string was threaded through the chicken wire and a "snoopy loop" attached. Twenty six detectors were required; each was stored in a thin plastic bag. Each detector was tested under the UV lamp before use. The cotton wool was totally clear of fluorescence but specks of blue were noticed on some of the twists of the chicken wire. (The specks were also visible after immersion but appeared to stay the same size and, more importantly, did not affect the cotton wool). (Photo showing lamp and detector - Phil Papard)

Optical Brightening Agent
Tinopal CBS-X optical brightening agent powder was double-bagged in 300g portions and the plastic bags placed for transport to Spain inside solid plastic boxes with press-fit lids. The lamp was used to ensure that no OBA contaminated the external surfaces of the boxes.
An Internet search revealed some possible difficulties in dissolving the powder straight into cold stream water. The OBA had to be dispersed into the stream water as quickly as possible - carrying the OBA into the cave as a colloid or solution was thought to be the answer.
Six 4 litre paraffin containers (with the original, close fitting lids) were obtained. Approximately rectangular, each fitted snugly into its own tackle sack for underground transport.

Method for dissolving the OBA powder
: 3 litres of water in a large pan was kept at approximately 70C over a gas stove. Cold water was dribbled over 30g of the powder in a measuring jug and stirred with a spoon to create a lump-free slurry. Some of the hot water was slowly added from the pan to create a thinner slurry. This was then slowly poured into the pan, stirring as it was added. Further portions were added using the same method until it appeared that little more of the slurry would dissolve or disperse. Approximately 350g dissolved in a total of about 3.5 litres of the hot water. The concentrated solution was poured into the paraffin containers and allowed to cool. The dissolving method was repeated for the other 5 containers ending up with a total of 2.1kg of OBA dissolved in 21 litres of water.

Detection methods
At each of the three resurgence sites, two detectors (left and right) were used. Each was placed in a strong flow, possibly with the flat face towards the current. At Fuente Aguanaz the detectors were attached to the iron grid covering the water collection pipe in the cave upstream of the resurgence. At Los Boyones in Secadura, the detectors were placed close to the vertical abstraction pipe. At Arronte (photo: Phil Papard), the detectors were placed over water welling up from the stream bed within a metre of a grid over a stream bank opening.
Visits were generally made every two or three days to remove one detector alternately, so that each overlapped the other, usually up to five days. During the three weeks, one flood episode (photo: Phil Papard) required almost complete immersion at Los Boyones in order to recover a detector about 1.5m under water. After that, the detectors at this resurgence were tied back to a much higher anchorage.
The first 4 days were taken up with background testing to eliminate any OBA in the water from, e.g. clothes washing. All detectors remained negative.
On "Day Zero", a team of eight cavers carried the 6 containers of OBA solution into the Sumidero de Cobadal. It was poured into the stream (photo: Andy Morse) at the boulder chamber below the 5m pitch, more than a kilometre underground on a straight line bearing from the entrance of 102º (Grid reference of this point is approximately 30T 0449764 4797788 altitude 168m). Although the OBA had started to precipitate out of solution it quickly re-dissolved as it entered the stream water.

   This table summarises the schedule of detector placement and removal, along with the water levels and the results. The prime result was the positive detection of the optical brightener at Fuente Aguanaz after 5 - 7 days. The detectors at Fuente Aguanaz remained positive to the time when all the detectors were removed from the resurgences on day 14. All other detectors at the other resurgences remained negative throughout the test.

   We can conclude that the water disappearing at the end of the Sumidero de Cobadal resurges at Fuente Aguanaz.

- It is also likely that any water sinking over the supposed underground route of the water will also resurge at Fuente Aguanaz.
- Although the main conclusion is clear and unambiguous, it does not mean that the water may not flow to other places at different water stages.
- The large size of the resurgence (1.5 x the flow from Boyones) suggests a large catchment - perhaps up to Alisas - and an extensive network of cave passages. Los Boyones has 43km of known cave passage behind it. At present, there is only 1.5km behind Fuente Aguanaz.
- This map shows some of the water flows associated with Fuente Aguanaz and Los Boyones.

   The successful test was the result of a team effort from a number of people who became involved. Thanks are due to all of the following:
Ian Chandler (who completed the detector exchange regime after most people had returned home), Dave Cooke, Jenny Corrin, Penny Corrin, Harry Long, Lank Mills, Andy Morse, Phil Papard, Andy Quin, Bill Sherrington, Pete Smith, An Vanderplank, Dr Terry Whitaker, Jon Whiteley, Les Williams, and not least, Fernando Fernández Labadie at the Dirección General De Obras Hidráulicas Y Ciclo Integral Del Agua, Santander.

Juan Corrin, June 2006