Peņas Blancas Section: Poco Sol to San Isidro
Degree of Difficulty: Class IV
Gradient: 115 feet per mile 1 @ 214 (22 m/km; 1.6 @ 41)
Length: 4.0 miles (6.4 km)
Put-in Elevation: 1246 feet (380 m)
Take-out Elevation: 787 feet (140 m)
Drainage Area: 43 square miles (112 km2) at put-in
Average Discharge: 587 cfs (17 cms)
Season: Wet season only in September to November
The Peņas Blancas (PEH nyass BLAHN kahss) is one of the recently-discovered whitewater gems of Costa Rica's Caribbean slope. This incredible stream was not paddled until November of 1986, when a small party led by the authors accomplished the first descent. The extreme gradient of the third mile led to considerable misgivings prior to the attempt, but with party members Bill Karls, Paul Mason, and George Strickland the group pressed on with some trepidation. What we discovered on that first run was not unrunnable waterfalls, but rather, some of the finest scenery and whitewater in the region.
Descending from the crest of the Cordillera de Tilaran, the Peņas Blancas (white stones) drains an area of only 43 square miles above the upper gorge. In almost any other area of the world, such a tiny drainage basin would produce only a tiny creek, but this mountainous region receives over 200 inches (5000 mm) of rain per year on its upper slopes, yielding a channel of more than adequate size, with abundant runoff. Because the stream drains a densely forested area including parts of the lush Monteverde Forest Reserve, water quality is excellent.
The upper section of the Peņas Blancas flows through a dramatic gorge where the river has incised itself into the mountain escarpment. Below Poco Sol, there is little disturbance of the native jungle flora and canyon walls rise to a height of over 700 feet (200 m). Dozens of sulfurous hot springs emerge from the young basaltic lavas and birds of spectacular plumage seem to infest every tree.
Access to the put-in at Poco Sol is from the south side of the river. A very rough dirt road leads from the small community of San Jose towards the put-in, although only four wheel drive vehicles will be able to make it all the way to the put-in (see map). Most vehicles will have to stop about one-half mile (.8 km) short of the river, but the carry is made easier by the steep downhill approach. The put-in is beneath the hanging bridge.
One hundred yards past the put-in, the river swings hard left and drops through a steep drop that is severely constricted by large boulders. This one should most definitely be scouted, for it is the most difficult and dangerous rapid on the river, with several potent holes obstructing the direct route through it. This rapid is a marginal Class V, but it is the only one on the river. Unfortunately, it occurs immediately after the put-in and the paddler has no opportunity to warm up before entering it. This rapid has been named Tranquilo, Tranquilo--loosely translated, it means "take it easy". An easy portage could be made on the right.
For the next mile and one-half (2.4 km) the river drops over numerous rapids of low Class IV difficulty. All of them are straight forward and lend themselves to careful boat scouting. The fourth rapid in this sequence has a large pourover hole that should be easy to avoid, but as its name (Pablo y Miguel) suggests, a couple of us failed to do so on the first descent. In the middle of this section is a rapid where the river swerves against the left wall and has succeeded in carving a large cavern in the cliff. One can eddy out in the middle of the rapid in a rock shelter that is at least 20 feet (6 m) deep and 15 feet (5 m) high.
As the river approaches a much narrower lower gorge, the gradient increases to 214 feet per mile (41 m/km) for an entire mile. Such an extreme gradient often results in unrunnable rapids but the Peņas Blancas accomplishes the descent in one long, continuous rapid. Spread out over a mile without a single pool, this 214 foot drop is only Class III+ in difficulty; it is a whitewater delight rather than a nightmare. We named this rapid Casado Especial. Its namesake is a traditional Costa Rican meal with rice, beans, meat, spaghetti, eggs, salad, potatoes, tortillas, etc. The rapid contains a similar quantity and variety of whitewater delights.
The last mile has a much lower gradient but many fun rapids remain and the intervening pools provide an opportunity to enjoy the scenery and wildlife of the canyon. The high bridge outside of San Isidro marks the end of the canyon run of the Peņas Blancas. A steep trail leads to the road from the right bank.
As the deep, widely scoured floodplain suggests and the accompanying hydrograph confirms, the Peņas Blancas is prone to rapid increases in streamflow. The steep slopes of the headwaters gather the torrential rains that fall on the Cordillera de Tilaran very efficiently, sending them down the small tributaries and into the main canyon in very impressive volumes for a stream with a drainage basin of only 43 square miles (110 km2).
Great care must be taken, then, in deciding to run the upper canyon. No gage is available at or near the put-in, but an appraisal of flow conditions can be made from the bridge at San Isidro. At runnable levels, the rapids below the bridge should appear runnable but scratchy. If the rapid downstream of the bridge indicates voluminous flows with large standing waves, the lower section would be a better bet. If the channel is full from bank to bank, head back to the Sarapiqui.
