Gamboa Site Description

Gamboa is a small town located at the confluence of the Rio Chagres and Lago Gatun, historically it has been the home of the canal dredging division. Currently, the Smithsonian Tropical Research Institute (STRI) has established a research and education field station in Gamboa, owning several tracts of land. Located within Gamboa is Cerro Pelado a steep hill owned in part by STRI, Universidad Technologica de Panama (UTP), and Autoridad de Canal del Panama (ACP). Cerro Pelado was chosen as the research site for detailed field studies due to the relative ease of access and the established STRI laboratory facilities nearby. Cerro Pelado is quite steep abruptly rising from 30 to 223 m above sea level (asl) as shown in Fig 1. During early canal operations (1920s or later) Cerro Pelado (bald hill literally translated) was clear-cut and can now be considered as well established second growth. True triple canopy conditions typical of pristine tropical catchments are not found on Cerro Pelado with the situation more accurately described as two and a half layer canopy. Deciduous trees reaching 25 m with several larger trees reaching 35 m dominate the average canopy height in the vicinity of the tower. By far the most prevalent trees seen are various species of palm reaching 25 m and combined with emerging deciduous trees form the secondary canopy layer. Some smaller palm trees and undergrowth of a few meters are seen in varying degrees on the hillside.

Further details on the methods employed to gain a better understanding of the unique mechanisms repsonsible for tropical runoff production can be found by selecting the method of choice from the menu found to the left. Location of important equipment used for field work in Gamboa are shown by Fig 2 where T is the tower, TF1-TF2 are throughfall collection troughs, numbers 1-4 are soil moisture nests, S1-S4 are stream gages, g1-g5 are groundwater monitoring wells, SF is a stemflow collection nest, and tr is a throughflow trough. An aerial photographic representation of Fig 2 with contours and site locations overlayed is shown in Fig 3.

Fig 1 Three dimensional representation of the Cerro Pelado research area owned by STRI and UTP, view on backside of the hill draining toward the Gamboa Rainforest Resort.

Fig 2 Topographic map noting important instrumentation sites found on Cerro Pelado.

Fig 3 Aerial photographic represenatation of the Gamboa study area with contours and equipment locations overlayed. As usual click on the photo for a better resolution image and the location of some Gamboa hotspots. Some minor discrepancies may exist with the GPS points since this image was manually geo-referenced.

Climate

The movement of the inter-tropical convergence zone (ITCZ) more or less controls the climate of Gamboa and indeed all of Panama. Broadly the ITCZ is responsible for the rainy seasons that we so closely associate with tropical rain forests. In Panama the rainy season generally persists from May until December and the dry season from January until late April. Panama additionally has a rainfall gradient that is oriented from the Caribbean to the Pacific oceans with the former receiving much more rainfall. The Caribbean receives much more rainfall because the moisture-laden trade winds are primarily oriented from the northeast during the dry season. Gamboa being located in almost exactly the middle of the country exhibits a marked seasonality in rainfall with an average annual rainfall of 2148 mm.

A detailed climatological record exists at Gamboa because of canal operations with rainfall records dating back as far as1897. Fig 4 gives the monthly distribution of rainfall at Gamboa highlighting the pronounced wet and dry seasons. Gamboa receives less than 20 mm of rainfall during the months of February and March, while October is the wettest month receiving 306 mm of rain on average. While not as prevalent in the Gamboa historical records as other locations in Panama there is a period of slightly decreased rainfall in July and August referred to as the Veranillo de San Juan. Veranillo de San Juan can last anywhere from one to four weeks and is generally accompanied by an increase of wind speed (Espinosa 1998). General meteorological values dating back to 1979 are averaged for each day of the year and shown in Fig 5 with each data point representing a 25-year average. The temperature variability is remarkably small throughout the year with the mean temperature of 26.4 C. The relative humidity increases and solar radiation decreases as would be expected with the onset of the wet season. Interestingly, the average daily wind speed decreases dramatically with the onset of the wet season. There is also a small local minima during the months of July and August probably due to the Veranillo de San Juan.

Fig 4 Monthly averages of rainfall in Gamboa with records dating back to 1897 because of Canal operations.

Fig 5 Daily averages of meteorological observations of a.) minimum, daily average, and maximum temperature, b.) wind speed, c.) relative humidity, and d.) total incident radiation.

Espinosa, J. A. (1998). Veranillo de San Juan within the Panama Canal Watershed. Balboa Heights, Panama, Panama Canal Commission: 10.