by Ernest W. Tollner, University of Georgia, Athens
he Alabama-Georgia PD/A CRSP project is applying a comprehensive systems research approach to assess and foster the development of small to intermediate-sized tilapia production enterprises in Honduras and other Central American countries. Development of reliable and sustainable water supplies is a key ingredient in any inland aquacultural enterprise. In this article, we review the progress toward water supply development in Honduras.
Honduras is a Central American country of approximately 11 million hectares with both Atlantic and Pacific coasts. Mountains may be as high as 2,600 meters. Rainfall varies from 600 mm to 3,400 mm annually, with the highest precipitation generally associated with higher elevations. Temperatures above 1,300 meters are usually too cool for tilapia production. Rainfall is unevenly distributed in the elevations where tilapia would most likely be produced, which requires innovative schemes for water supply development.
The current state-of-the-art approach for supplying small to medium-sized communities with water for a variety of uses (including ponds) is the water tube-spring. PVC or polyethylene pipe (12 mm to 25 mm in diameter) is run down slope from a naturally occurring spring to a site, which may be a kilometer or more from the spring. Springs are prevalent in mountainous areas at altitudes below 1,300 meters. The excavated levee pond is currently the most popular containment for fish production. The watershed pond is not widely used because the steep valleys do not readily enable suitable diversion spillways for adequate handling of high runoff rates during rainy seasons.
Several assumptions were made at the project outset. First, we assumed that interested nongovernmental organization (NGO) staffers would be willing to devote time to learning how to evaluate topography and soils for pond suitability. Second, we assumed that these NGO staffers would be able to obtain and load EXCEL®-based software onto their computers. Experience with workshops conducted to date suggests that both assumptions are realistic.
The modeling effort was separated into water supply feasibility and economics phases. EXCEL®-based models were developed for evaluating feasibility and costs of levee ponds and hillside ponds. The difference between the levee pond and the hillside pond in this report is that the levee pond must be supplied by pipe while the hillside pond may capture runoff from surrounding areas. The hillside pond is intended to supply water for a variety of uses including fish production. The levee pond is the primary containment for fish production. Levee and hillside ponds are of similar construction.
The feasibility of a levee pond size in a given area was evaluated by determining the peak, average, and minimum monthly water balance (see Figure 1). The model predicts the supply flowrate required to maintain a full pond given the pond surface area, depth, and climate variables (evaporation, seepage, and precipitation) in the region.
The hillside pond model evaluates the feasibility of developing a sustainable pond with springs and surface water runoff. As previously stated, placing a watershed pond in the main runoff conveyance is likely not feasible due to steep valley slopes. One approach for using a watershed type pond in capturing water is shown in Figure 1, wherein a pond is located out of the main channel and supplied with an excavated ditch which connects with the main drainage conveyance at some point upstream. A diversion structure may be designed to capture nearly all of the runoff during dry months and a small fraction of the runoff during the rainy season (see Figure 2). Water in this pond may be used for a variety of uses including fishpond supply. The EXCEL®-based model performs a water balance (see Figure 3) as with the levee pond with the addition of runoff prediction from the watershed above the pond.
With the help of Dan Meyer, Suyapa Meyer, and George Pilz of Escuela Agrícola Panamericana El Zamorano, a daylong workshop for local NGO staff and Zamorano faculty was conducted. The program was structured into morning lecture sessions and an afternoon field trip. The hillside pond model and the levee pond models were demonstrated using slides in English accompanied by handouts in Spanish. The Excel® models were partially translated into Spanish, with the translation service provided by CRSP-sponsored Honduran students studying with Joe Molnar at Auburn University. The workshop was very well received. Faculty members at Zamorano are using parts of the presentation in classes at Zamorano. The success of this workshop is providing the basis for future workshops to be held in Guatemala and El Salvador. The models are being made available on the web by the Red de Desarrollo SostenibleHonduras (RDSHN), an NGO with extensive capacity in information technology serving over 700 customers and NGOs with Internet facilities on the RDS website.
Future goals include completing the Spanish translation of the models. We also plan to move the models to a more friendly web-enabled platform. The main disadvantage of using any package for model development is that the user must have the package. Using a common spreadsheet such as EXCEL® probably minimizes the disadvantage; nonetheless disadvantages remain, such as the substantial programming required to make the models applicable or relevant to different geographic regions. Moving the models to a web-enabled platform will allow us to use a more conventional programming platform that can be placed on a central server for universal web access.