Costa Rica has an abundance of water. Annual rainfall totals reach as high as 350 inches in parts of the country, and the Central Valley is considered to be a "dry" area because it receives only 70-90 inches of rain per year. The significance of this is not so much that abundant water is available, but that even small watersheds gather enough runoff to be paddleable. In the most humid sections of the U.S., few watersheds smaller than 150 square miles have enough water in them to kayak for significant portions of the year.
The Chattooga River, for example, drains 207 square miles of the wettest area in the eastern U.S. Most paddlers consider the Chattooga to be a small river, as its average summer discharge is approximately 400 cfs. The Pacuare River of Costa Rica drains an area of only 142 square miles above the upper put-in but has an average discharge of 1230 cfs. The Peñas Blancas is runnable where the upstream drainage area is a mere 43 square miles. As a result of their heavy runoff loads, small watersheds in Costa Rica produce runnable streams, whereas a watershed of comparable size in the states would yield only a tiny creek.
Of perhaps greater importance to the paddler who goes to considerable trouble and expense ito travel several thousand miles to reach this area is the reliability of stream flows. Many of the streams in this region are within the envelope of paddleable flows for much of the year. More importantly, the flows for any particular month of the year are more reliable than those of North America. Streamflow is so reliable here because the variability of precipitation is quite low throughout the humid tropics. The systems that bring rain in the equatorial zone are relatively stable and reliable, unlike the erratic storm systems that move through the mid-latitudes following the fickle jet streams.
While adequate flows are quite reliable, excessive flows can be a problem, especially during September and October. A commercial raft trip from Costa Rica Expeditions was forced to remain in camp for two days of high water on El General in 1984. The members of the group were preparing for an arduous hike out of the canyon when the river finally dropped and they were able to complete their trip. The great variability of flow levels on the General is further exemplified by the flash flood of October 2, 1982, when the river rose more than five feet in less than an hour to reach a discharge level of 26,000 cfs. The river dropped just as quickly to a discharge of less than 10,000 cfs by the following morning.
A party of guides was caught by rapidly rising waters on the Pacuare on Christmas eve of 1989. As they tried to evacuate the canyon by river at dawn, a huge surge caught them just below Cimarrón rapid, flipped all of the rafts and scattered swimmers for two miles on both sides of the river. Several such episodes have occurred on the Reventazón as well as the Pacuare.
Abundant late-afternoon and early evening rainstorms frequently cause river levels to rise dramatically during the night, so it is important to carry boats well above the water line when stopping for the night. This should also be considered when choosing a campsite. Episodes such as those described above underline the importance of preparation for changing water levels. A margin of ten vertical feet should be allowed for on most rivers
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