Thalweg Travelers

My January 2020 Geography of Coffee travel course in Costa Rica included a bonus country: Panama.

Bribrí community houses. Image: Stribrawpa
These houses are in Costa Rica, but the photographer
may have been standing in Panama (see below).

Without any paperwork, immigration officers, customs declarations -- or even a sign indicating we had done so -- we visited a country that was not listed on our itinerary and for which we have no passport stamps. This was possible because of several aspects of the human and physical geography of the Bribrí community with which we enjoyed an overnight visit.

Specifically, we were visiting the Stibrawpa cooperative in Yorkin, which is one of more than a dozen Bribrí villages in the Talamanca Bribrí Indigenous Territory, which in turn is part of La Amistad (Friendhip) International Park, a UNESCO World Heritage site.

The most accessible (by road) of the Bribrí settlements include one known as Bambú, where our group was greeted by a community leader who took us to the two dugout canoes that awaited us. Each was cut by hand from a single tree trunk, equipped with a small but powerful outboard motor, and driven by a captain in the stern and an expert first mate with a pole in the bow. That mate watched for obstacles, fended off rocks with his long pole, and occasionally used the same pole for propulsion, adding his muscle power to what the engine could provide in shallow waters. It being a bit of a low-water day, there was a lot of heroic digging.

This wave to a passing boat might be across an international border.

Our journey took us just three miles or so, first down the Telire River and then up the Yorkin to a settlement of the same name. 

The current was against us for most of that distance; more importantly the rocky, meandering stream required constant vigilance on the part of the crew, who needed to follow the thalweg carefully from side to side. Everyone knows that rivers move water, but they also move rock and soil slowly but inevitably toward the sea (in this case the Caribbean).

Typically, deposits form on alternating inside curves of a river and it is scoured from alternating outside curves. The thalweg is the deepest part of the river, which sways from side to side, extenuating the already sinuous path that one would follow down the center. The point bars are generally impassable and often mainly above water; near the cutbanks water is deep enough for passage but the deep part may be narrow and can be quite swift. In the short straight stretches between bends, riffles (or rapids) may present uniformly shallow water from bank to bank.

Typical geometry of a meandering stream. Thanks to River Bum for the
diagram. Stream geometry is important for people who boat, who fish,
and who are interested in political geography.

Where a river forms a boundary between states or countries -- as the Yorkin does between Panama and Costa Rica in this area -- that boundary is most commonly defined as the centerline of the river. 

Lagniappe

I indicated that borders "most commonly" follow the centerline because I was remembering that between Ohio and Kentucky, the boundary is on one bank. I could not remember which bank; checking the map indicates that it is the right bank and also that the river has moved since that boundary was established. 

Detail from Google map of downtown Cincinnati/Covington.
Note that during the days of the Underground Railroad, enslaved
persons needed to cross the river completely to escape the South.

Family Geography Night: In April 2021, my colleague Dr. Vernon Domingo and I shared many more river stories during a special online version of Family Geography Night, an annual tradition at North Andover Middle School.