While Hinatuan’s Enchanted River Underwater Cave System (HERUCS) is undoubtedly the best cave dive the Philippines can offer at the moment, it is tempestuous. Many a diver have been literally spat out of the cave entrance from strong outflow current. Worse still, in the 12-meter access to Mayor’s Chamber where the current is strongest, the floor is lined by loose coarse gravel with nothing to do a pull-and-glide on. On the other hand, this author have been in a few times under the best circumstances – no current, unlimited visibility. Literally, much like swimming in a giant bottle of mineral water. The science of “Tides” as it relates to HERUC follows:
Fig 1 represents a typical tide chart for Hinatuan during the spring tide cycle (full moon or new moon). The red shaded area represents the flood tide where seawater flows towards HERUCS. The blue shaded area represents ebb tide where seawater recedes from HERUCS. In this particular chart of Hinatuan area (August 18, 2013), there is a wide exchange between high tide and low tide, providing for a very large red-shaded area signifying a big amount of seawater in the river and HERUC. The blue-shaded area represents the volume of water flowing out of HERUCS and Enchanted River. Common sense dictates that diving on the red side of the tide cycle affords one with the least chance of running into HERUCS’ vaunted outflow current as the seawater (specific gravity 1.028) flowing in holds and/or pushes the fresh water (specific gravity 1.000) back.
Diving The Chart
At Expedition V, we put this theory to the test. On day 1 (Sunday, August 18), we entered the water at 4PM. The water was green, very salty and with impaired visibility. We descended in this water condition and did not encounter the halocline until at the depth of 33 meters where the water abruptly changed into crystal clear typical of HERUCS fresh water. There was a slight current pushing us forward into the chamber. The dive was turned around at 4:16PM. At deco, moderate down current was encountered. At exit (6:01PM), there was still moderate down current. The visibility remained poor.
Dive #2 was planned at mid-upstroke of the chart. The head spring was crystal clear and with slightly brackish taste. All the way through the dive the condition remained – no current, unlimited visibility. Water at 3 meters at time of exit was brackish.
HERUCS diving can be most pleasant and exciting – at the right conditions. The chamber is at the deeper limit of “air” depth (maximum of 52 meters). Negotiating the slightly restricted access (Patrice’s way and Jake’s Bypass) and exploring the walls and ceilings give one a number of good dives on bottom gas of air and deco gases of 50% EANx and 100% O2. Of course, trimix diving Paul’s Passage to the depth of 87 meters and beyond raises the excitement to the nth degree. We at FCD believe that the ideal conditions for diving HERUCS are:
- Spring tide portion of the lunar cycle (full moon and new moon)
- The middle portion of the upstroke (flood tide)
- Clear, blue water
- Minimal or absent flow of the river out to sea
- Slight brackish taste to the water
Postscript: This conclusion was not tested against neap tide (first and third quarters of the lunar cycle) conditions.
Acknowledgement: Thank you to team members Jaime Lapac, Larry Williams and Rio Lapac. Thank you to Mayor Viola and Ferdinand Barrios for the direction and accommodations.