Management Plan for Water Use to Improve a Wildlife Refuge Surrounded by an Agricultural Community in Southwest Puerto Rico

Carlos J. Santos-Flores 1, Eric Harmsen 2, Alexis Cabarcas-Núñez 3, Dallas E. Alston 4 1 Department of Biology, PO Box 9012

2 Department of Agricultural Engineering

3 Puerto Rican Commercial Aquaculture Research and Development Center (CIDACPR)4 Department of Marine Sciences

University of Puerto Rico at Mayagüez Mayagüez, PR 00681-9012 USA

(a) Introduction: Include a clear statement of the long-term goal(s) and supporting

objectives of the proposed activities.

Our long-term goal to restore hydrologic function at Laguna Cartagena National Wildlife

Refuge.

Summarize the body of knowledge or past activities which substantiate the need for the

proposed project.

Describe ongoing or recently completed significant activities related to the proposed

activity including the work of key project personnel. Include preliminary data/information

pertinent to the proposed project.

In addition, include in-depth information on the following, when applicable:

(1) Estimates of the magnitude of the issues and their relevance to stakeholders and to

ongoing State-Federal food and agricultural research, education, and extension programs;

Lajas Valley is among the 3 most important agricultural areas in Puerto Rico. Important

agriculture stations belonging to the University of Puerto Rico are located in the Lajas Valley.

The University of Puerto Rico-Mayagüez Campus (UPR-M) is the major institution which offers

undergraduate education in Agricultural Sciences in Puerto Rico. UPR-M is also the only

institution with a graduate program in Agricultural Sciences in Puerto Rico, and the most

important instructional facilities are located within the Lajas Valley.

(2) Role of the stakeholders in problem identification, planning, and implementation and

evaluation as appropriate;

(3) Reasons for having the work performed at the proposing institution.

(b) Objectives: Include clear, concise, complete, and logically arranged statement(s) of

specific aims of the proposed effort in all proposals.

(c) Methods: Explicitly state the procedures or methods to be applied to the proposed effort.

Include, but do not necessarily limit to:

(1) Description of stakeholder involvement in problem identification, planning, implementation

and evaluation;

(2) Description of the proposed project activities in the sequence in which it is

planned to carry them out;

(3) Techniques to be employed, including their feasibility and rationale for their

use in this project;

(4) Kinds of results expected;

(5) Means by which extension and education activities will be evaluated;

(6) Means by which data will be analyzed and interpreted;

(7) Details of plans to communicate results to stakeholders and the public;

(8) Pitfalls that might be encountered; and

(9) Limitations to proposed procedures.

(d) Cooperation and Institutional Units Involved: Cooperative, multi-institutional

and multi-disciplinary applications are encouraged.

Identify each institutional unit contributing to the project and designate the lead institution or

institutional unit. When appropriate, coordinate the project with the efforts of other State and/or

national programs.

Clearly define the roles and responsibilities of each institutional partner.

(e) Facilities and Equipment: Report and briefly describe all facilities which are available for

use or assignment to the project during the proposed project period. Itemize all major equipment

or instrumentation available for use or assignment to the proposed project.

In addition, list all items of nonexpendable equipment needed to conduct and bring the project to

a successful conclusion, include dollar amounts and, if funds are being requested for their

acquisition, justify.

(f) Project Timetable: Outline all important phases as a function of time, year by year, for the

entire project, including periods beyond the grant funding period. Include specific, measurable

accomplishments for each year of NIWQP funding.

PHASE TIME ACCOMPLISHMENTS

Phase 1

Phase 2

Phase 3

Phase 4

Determine levels and topography.

Prepare topographic map of L.C.N.W.R.

Prepare stream cross sections at Quebrada de los Llanos

Prepare cross sections at the west canal

Prepare spot elevations at Maguayo

Prepare a bathymetric study of the lagoon

Conduct hydrologic-hydraulic analysis

Develop a water budget for the watershed

Develop a water budget for the lagoon

Determine water sources and volumes

Determine water needs

Determine how to manage the water resources to support proper

hydroperiods and water levels

Determine desired water levels for the lagoon

Avoid flooding Maguayo community

Avoid flooding private farms

Avoid back flow in the east canal

Determine if additional water is needed

If necessary, negotiate with P.R.E.P.A. to have more water delivered by

the Lajas Irrigation System

Improve quality of water flowing into Laguna Cartagena

Control runoff from Maguayo

Control runoff from sugarcane fields

Request E.P.A. and E.Q.B. to stop illegal sewage dumping from Maguayo

into the east canal

It is essential to prepare a detailed topographic map of Laguna Cartagena that includes the

lagoon and surrounding Refuge lands to design and locate water control structures; to determine

water levels and sources; and to select the preferred alternative to improve water quality.

Conduct a survey of selected areas where structural improvements are recommended by the

hydrologic-hydraulic study and determine hydraulic characteristics of the lagoon’s drainage

system.

Existing ground elevations must be field stalked at the 10.97 m (36 ft) contour all around the

lagoon, at the northern perimeter of the Refuge (on the transect lines), at the southeastern side of

the Refuge (near the Maguayo community), at the bridge over the canal entering the lagoon on

the east, at various points on the boundary between the Refuge and Maguayo, at the cement

house on the western outflow of the lagoon and at the cement stake on the western outlet of the

lagoon. This survey must tie in to the U.S. Geological Survey benchmark used to establish the

elevational datum for the U.S. Geological Survey’s former gage station. In that way previous

USGS water data can be used in the hydrologic evaluation of the Refuge with confidence.

The second phase of the topographic study should include stream cross sections in Quebrada de

los Llanos, and also at selected points in the drainage canal (west canal) between the lagoon and

Bahía Boquerón. The locations of these surveys must be determined in the field on the basis of

hydraulic considerations.

A hydrologic-hydraulic analysis of Laguna Cartagena is necessary to analyze and resolve

adverse implications of the proposed higher lagoon water levels. The study should include both

surface and shallow subterranean waters, including topics such as: water levels of the lagoon,

flooding problems at Maguayo, high groundwater table, hydroperiod, water budget and water

quality enhancement.

The hydrologic-hydraulic study should determine the hydrology of runoff from the hydrographic

basin of Laguna Cartagena (28 km2). The analysis also should consider the runoff of the 33 km2

area that discharges in the west canal that drains the lagoon.

The study should model and analyze the hydraulic characteristics of the system consisting of

Laguna Cartagena and the west canal. It should determine if there is a need to increase the

hydraulic capacity of the system.

The water quality analysis should include (as a minimum) sampling at (1) the main drainage

canal (northeastern canal), (2) the principal irrigation canal (east canal) at the entrance of the

Refuge and prior to being influenced by the Maguayo community, and (3) at the exit of the

lagoon on the west side. The impact of agricultural runoff and urban runoff from Maguayo

should be determined.

The hydrologic-hydraulic study should recommend a design and management plan, in close

coordination and collaboration with the Service’s staff. It should include a design for the lagoon,

its water control structures, placement of dikes, water diversions, pumps and improvements to

the drainage system downstream from Maguayo.

An increase in the lagoon’s water level could raise the shallow water table, causing water

logging and salinization of soils in adjacent areas. A ditch or a soil drainage system close to the

lagoon’s northern perimeter should be considered as a control measure.

It is important to document shallow ground water levels in the Refuge outside the lagoon. Data

should be obtained from a series of shallow piezometers as soon as possible. Observation wells

should be made within the Refuge, near each of the bench marks along the northern boundary of

the Refuge, along the three Maguayo roads, and along the lagoon’s outlet.

Initial water levels measured should include the water level on the east canal at the entrance of

Laguna Cartagena, on the bridge, and at the northeastern canal. Water levels should be measured

weekly.

*An operation strategy should be proposed to increase the lagoon’s water level while minimizing

maintenance costs, operational complexity, and adverse impacts on the Maguayo community and

other water users of the Lajas Irrigation System.

It is necessary to develop a water budget to determine water needs and sources of supply

required to create the desired hydroperiods and water levels to attain the restoration goals. The

water budget analysis will consider primarily surface inflow, surface discharges,

evapotranspiration and groundwater exchange.

A seasonal water budget analysis is required to determine the inflows needed to maintain the

proposed higher levels.

It is essential to determine if and how the additional water needs can be met from surface runoff

or whether it will require deliveries from the Lajas Irrigation System, representing a potential

conflict with other users.

REFERENCES

Aponte, F. 1984. Uso de agua en Laguna Cartagena, Lajas. Dept. Rec. Nat. de P.R.

Unpubl. Rep. 6 pp.

Arbelo, J., M. Berríos, H. Días-Soltero, M. Espinoza, M. Rivera and V. Rodríguez. 1989.

Ecological Inventory of Cartagena Lagoon, Puerto Rico. Unpubl. Paper. Univ. of

P.R., Mayagüez. 91 pp.

Carter, O. R. 1965. Soil Survey Lajas-Valley Area, Puerto Rico. U.S.D.A., Soil

Conservation Service. 188 pp.

Colón, H. E. 1980. Los vertebrados de la Laguna Cartagena. Unpubl. Paper. Univ. of

P.R., Mayagüez. 74 pp.

Colón, H. E. 1982a. La Laguna Tortuguero (sic. Cartagena): debemos preservarla.

Unpubl.

Colón, H. E. 1982b. Pasado, presente y futuro de la Laguna Cartagena. Unpubl.

Colón, H. E. 1982c. Laguna Cartagena: recomendaciones en una época de crisis económica.

Unpubl.

Colón, H. E. 1982d. Que la Laguna Cartagena pase a manos del Pueblo. El Mundo. 12

septiembre.

Colón, H. E. 1982e. La importancia de la Laguna Cartagena para la preservación de especies de

aves en Puerto Rico, pp. 145-147. In: Noveno Simposio del Departamento de Recursos Naturales

de Puerto Rico, San Juan.

Cotté, R, 1956a. Unpubl. Letter to Mr Félix Iñigo. 1 pp.

Cotté, R, 1956b. Unpubl. Letter to J. McCandless. 1 pp.

Cotté, R, 1956c. Quarterly Progress Report for Inverstigations Projects. Project number W-8-R-

1. Unpubl. Rep. 1 pp.

Cotté, R, 1956d. Unpubl. Letter to A. Aguilar. 1 pp.

Cotté, R, 1956e. Unpubl. Letter to J. McCandless. 1 pp.

Cotté, R, 1957a. Quaterly Progress Report for Puerto Rico Waterfowl Habitat Studies (Cartagena

and Tortuguero Lagoons). Project number W-8-R-1. Unpubl. Rep. 5 pp and field data.

Cotté, R. 1957b. Birds watched at Cartagena Lagoon and its surroundings. Unpubl. Rep. 8 pp.

Cotté, R. 1957c. Draft Quarterly Progress Report for Puerto Rico Waterfowl Habitat Studies

(Cartagena and Tortuguero Lagoons). Project number W-8-R-1. Unpubl. Rep. and 4 maps. 23

pp.

Cotté, R. 1957d. Draft Quarterly Progress Report for Puerto Rico Waterfowl Habitat Studies

(Cartagena and Tortuguero Lagoons). Project number W-8-R-1. Final Unpubl. Rep. 16 pp.

Cotté, R. 1957e. Notes on the physical, chemical and ecological (flora and fauna) characteristics

of Cartagena and Tortuguero Lagoons. Puerto Rico Waterfowl Habitat Studies. Project number

W-8-R-1. Unpubl. Rep. 21 pp.

Cotté, R. 1957f. Kill Data on Cartagena Lagoon, Guánica Lagoon and El Anegado from 1950 to

1957. Unpubl. Rep. 2 pp.

Cotté, R. 1958a. Progress report of exotic and native plants found in and around Tortuguero and

Cartagena Lagoons, period: Jul 1957-Jun 1958. P.R. Waterfowl Habitat Studies. Project # W-8-

R-2. Unpubl. Rep. 7 pp.

Cotté, R. 1958b. Quarterly Progress Report for Puerto Rico Waterfowl Habitat Studies

(Cartagena and Tortuguero Lagoons). Project number W-8-R-3. Unpubl. Rep. 10 pp.

Cotté, R. 1958c. Censo poblacional de aves en la Laguna Cartagena. Unpubl. Rep. 2 pp.

Cotté, R. 1959a. Análisis y composición final de Estadísticas de Caza para la recién pasada

temporada de acuáticos. Bureau of Conservation, Dept. of Agriculture and Commerce, P.R.

Unpubl. Letter. 6 pp.

Cotté, R. 1959b. Informe annual 1958-1959 para el proyecto número W-8-R-3 “Waterfowl

habitat and population studies of Cartagena and Tortuguero Lagoons”. Unpubl. Draft Rep. 4 pp.

Cotté, R. 1960a Data on hunters that visited Cartagena and Boquerón, species and number of

birds killed. Unpubl. Draft Rep. 2 pp.

Cotté, R. 1960b. Waterfowl habitat and population studies of Cartagena and Tortuguero

Lagoons. Puerto Rico Waterfowl Habitat Studies. Project number W-8-R-4. Pittman-Robertson

Federal Aid Report. Unpubl. Draft Rep. 6 typed pp.

Cotté, R. 1960c. Waterfowl habitat and population studies of Cartagena and Tortuguero

Lagoons. Puerto Rico Waterfowl Habitat Studies. Project number W-8-R-4. Pittman-Robertson

Federal Aid Report. Unpubl. Draft Rep. 24 hand-written pp.

Cotté, R. 1961. Estadísticas Finales para la Temporada de Cacería 1960-1961 en Laguna

Cartagena y Manglares Boquerón. Unpubl. Rep. 10 pp.

Danforth, S. T. 1926a. Christmas bird census, Cartagena lagoon, Southewestern Porto Rico.

Bird-Lore. P. 52.

Danforth, S. T. 1926b. An Ecological Study of Cartagena Lagoon, Porto Rico, With Special

Reference to the Birds. J. Dept. Agric. Porto Rico, 10:1-136.

Danforth, S. T. 1928. Christmas Bird Census, Cartagena Lagoon, Porto Rico. Bird-Lore, 50:68-

69.

Del Castillo, C., P. Torres Baez y S. Matos. 1985. Estudio ecológico de la Laguna Cartagena,

P.R. Unpubl. Paper Univ. of P.R., Mayagüez. 56 pp.

Department of Natural Resources of PR. 1985. Regulation to govern the management of

threatened and endangered species in the Commonwealth of Puerto Rico. 34 pp.

Erwin, K. E. 1989. Freshwater Marsh Creation and Restoration in the Southeast. In: Wetland

Creation and Restoration: The Status of the Science. Vol. I. Environmental Protection Agency

EPA 600/3-89/038a. Pp. 239-271.

García-Moll, A. 1983a. Suplemento Técnico para la Reserva Natural de Laguna Cartagena Valle

de Lajas. Dept. Rec. Nat. de P.R. 134 pp.

García-Moll, A. 1983b. Resumen sobre la importancia de Laguna cartagena. Dept. Rec. Nat. de

P.R. Internal memorandum. 2 pp.

Liogier, H. A. and L. F. Martorell. 1982. Flora of Puerto Rico and adjacent islands: a systematic

synopsis. Editorial de la Univ. de P.R., Río Piedras, P.R. 342 pp.

López, F. 1989. Final Report: Cartagena Lagoon Contaminants Survey. Caribbean Field Office,

U.S. Fish and Wildlife Service, Boquerón, P.R. 13 pp.

McCandless, J. B. 1961. Bird Life in Southwestern Puerto Rico: I. Fall Migration. Carib. J. Sci.,

1(1):3-12.

McCandless, J. B. 1962. Birdlife in Southwestern Puerto Rico: II. The Winter Season. Carib. J.

Sci., 2(1):27-39.

Molinares, A. 1981. Reproduction and morphology of the West Indian Ruddy Duck in Puerto

Rico. M.S. Thesis, Oklahoma State Univ., Stillwater. 48 pp.

Morales, D. and G. Fuentes. 1989. Documento de Designación Reserva Natural Laguna

Cartagena. Dept. Rec. Nat. de P.R. 49 pp.

Ortiz Rosas, P. 1981. Guía del cazador: aves de caza y especies protegidas. Dept. Rec. Nat. de

P.R. 119 pp.

Raffaele, H. A. 1974. Research on Puerto Rico waterfowl. Annual Performance Report for 1974.

P.R. Department of Natural Resources.

Raffaele, H. A. 1989. A guide to the birds of Puerto Rico and the Virgin Islands. Princeton Univ.

Press, Princeton, N.J. 254 pp.

Sedgwick, J. A. and D. W. Belisky. 1979. Island waterfowl Investigations Final Report. Puerto

Rico Dept. of Natural Resources. 80 pp.

Soil Conservation Service, Caribbean Area. 1973. Plants used as bird food. U.S.D.A. 18 pp.

Struthers, P. H. 1923. Observations on the bird life of Porto Rico. Auk. Pp. 469-478.

Wetmore, A. 1916. Birds of Porto Rico. U.S.D.A. Bull 326.

Eric Harmsen’s Sections

JustificationThe Laguna Cartagena is in direct connection with the underlying groundwater system. A portion of the laguna water is derived from the alluvium material deposited near the surface, and a portion from the upward flow of water through the fractured limestone aquifer. Laguna water originating from groundwater recharge within upland agricultural land may contain elevated nitrates and/or pesticides. Laguna water originating within the limestone aquifer may contain elevated dissolved solids. By using a groundwater flow model in combination with a particle tracking technique it will be possible to predict the source of the Laguna Cartagena water quality. Furthermore, the model will be capable of evaluating the effects of various water management practices within the watershed on the Laguna Cartagena water level.

Objective

1. Characterize the surface and subsurface flow systems of the Lajas Valley, with emphasis on the hydrologic interrelationships between these systems and the Laguna Cartagena.

2. Develop a numerical groundwater flow model for predicting groundwater levels and flow directions within the Lajas Valley.

Background

The Lajas Valley is located in the extreme southwest of Puerto Rico (Figure 1). The 130 square km valley is oriented in an east-west direction, 35.4 km in length and 6.4 km in width. Unconsolidated material fills the valley which is flanked on the north and south by volcanic and

limestone rocks of Cretaceous age. Historically, the area has had problems due to water logging and high salinity of the groundwater and soils. Anderson (1977) presented a detailed study of the hydrologic resources of the Lajas Valley. A summary of the hydrologic characteristics of the Lajas Valley are presented below.

Figure 1. Location of Lajas, PR (Magaly Revera, 2003).

The valley is a closed desert basin similar to those found in the Southwest U.S. Fine grained alluvium exists throughout the middle of the valley, while coarser grained material is found in the alluvial fans along the foothills. Five soil associations exist within the valley including the Fraternidad-Aguirre-Cartagena, Fé-Guánica-Aguirre, Americus-Guayabo-Sosa, Guayama-Aguilita-Amelia, Descalabrado-Jacana-San German Associations. Figure 2 shows the areas associated with the five soil associations. Figure 2 also shows the general layout of the valley, including the location of the Laguna Cartagena and the network of irrigation and drainage channels.

Figure 2. Soil Associations in Lajas Valley, PR.

Rainfall varies from approximately 45 inches per year in the north area to less than 30 inches per year along the southern coast. Evapotranspiration is between 30 in per year in the non-irrigated areas to over 50 inches per year in the irrigated areas. Aquifer recharge comes from intermittent stream that head in surrounding mountains. While some of the floodwaters reach the “playa,” most of the surface runoff enters the alluvial fans where it recharges the alluvial aquifer. Groundwater in the western Lajas Valley principally discharges to the Bahía Boquerón. In the eastern portion of the valley groundwater under artesian pressure, leaks upward through relatively impermeable soil, where it is lost to evapotranspiration from the soil or seeps to drainage canals.

Water table or unconfined aquifers occur generally within the alluvial fans and mountain areas along the north and south. Alluvial fans in the foot hills consist primarily of sand and gravel material. In the northern area, water withdrawn from alluvial fans is of high quality (i.e., low salinity). Alluvium filling the central portion of the valley is mainly silt and clay material interspersed with sand stringers. Water withdrawn from this material tends to be brackish. Aquifers also occur within the consolidated limestone and sandstone units. In La Plata basin in the northeastern part of the valley, wells tapping limestone overlain by less permeable alluvium are confined or artesian (i.e., the wells penetrating this unit are flowing wells). Confined aquifers also occur in the eastern central portion of the valley near the Ciénaga El Anegado-Laguna de Guánica. The volcanic rock which bounds the valley in the north and south are nearly impermeable.

In the Laguna Cartagena area the major aquifer is a buried limestone unit, is highly permeably and considered to be unconfined. Water levels in the vicinity of the Laguna Cartagena in March 1965 were approximately 3 m (above mean sea level), and water levels in the extreme eastern portion of the valley were around 9 m. Water levels in the foothills were around 17 m (Figure 3). Typical annual groundwater level fluctuations are on the order of 1 m. In March of 1986, groundwater elevations were significantly higher near the Laguna Cartagena (13 m), but were lower in the extreme western portion of the valley (2 m) (Figure 4). Figure 4 clearly shows that a groundwater divide corresponding with East-West Drainage Divide.

Figure 3. Groundwater elevation within the Lajas Valley alluvial aquifer, March 1965 (Anderson, 1977).

Figure 4. Groundwater elevation within the Lajas Valley alluvial aquifer, March 1986

(Graves, 1991).

As a part of the Lajas Valley study, Anderson (1977) developed a computer model to analyze the potential use of a series of pumping wells to reduce water logging in the vicinity of Laguna de Guánica. The transient computer model simulated flow only in the upper alluvial aquifer. From the report it was difficult to determine the size of the model; apparently it was limited to the area of interested and did not include the entire valley.

Materials and Methods

1. Review of existing literature

As part of Objective 1, the surface and subsurface flow systems of the Lajas Valley will be characterized, with emphasis on the hydrologic interrelationships between these systems and the Laguna Cartagena. Numerous studies have been conducted on the Lajas Valley, considering for example, agricultural drainage and salinity, geology and water resources. A geographic information system (GIS) has recently been developed for the Lajas Valley (Perez Alegria, 2003), which includes information on soils, streams, areas of flooding, salt-effected areas, farms, roads, and the irrigation and drainage canals. The GIS will be of great value in the development of the proposed numerical groundwater flow model.

2. Field Study

It is necessary to determine the current conditions within the valley with respect to groundwater levels, especially in the vicinity of the Laguna Caragena. As part of the scope of work, permission will be obtained for measuring water levels within the approximately fifty existing wells within the alluvial aquifer. Approximately eight wells will be installed in the alluvial aquifer where data is lacking. All new wells will be installed in compliance with EPA standards for chemical sampling and for measuring piezometric head. A groundwater elevation map will be developed for the entire valley for comparison with historical groundwater elevation maps. Water levels will also be obtained within the deeper bedrock aquifer to estimate vertical hydraulic gradients. All wells will be sampled for dissolved ions for the purpose of assessing the distribution of salinity within the groundwater systems. Nitrates will be evaluated to assess loading from agricultural land and a limited number of samples will be analyzed for pesticides. [CARLOS, CAN YOU DISCUSS METHODS TO BE USED FOR CHEMICAL ANALYSIS OF WATER]

3. Groundwater Model

A numerical groundwater flow model will be developed for predicting groundwater levels and flow directions within the Lajas Valley. As an integral part of the model development a conceptual model of the hydrologic environment will be developed. A conceptual model represents our best understanding of the system both qualitatively and quantitatively. The conceptual model includes the following components: topography and soils, climate, geology, hydrologic properties, aquifer properties (e.g., aquifer and confining layer thicknesses, hydraulic conductivity, storitivity, etc.), aquifer recharge, aquifer discharge, groundwater levels (historical trends), tidal effects, groundwater flow directions, distribution of pumping wells and pumping rates, saltwater intrusion soil and groundwater contamination, and aquifer transport properties.

A groundwater model will be constructed using the USGS Modular Three-Dimensional Ground-Water Flow Model (MODFLOW) developed by McDonald and Harbaugh (1984). Because of its ability to simulate a wide variety of systems and its rigorous USGS peer review, MODFLOW has become the worldwide standard groundwater flow model. MODFLOW is used to simulate systems for water supply, contaminant remediation and mine and construction dewatering. MODFLOW has been the recognized standard model used by courts, regulatory agencies, universities, consultants and industry.

The GIS-based user interface GMS (Groundwater Modeling System; Brigham Young University, 1997) will be used to manipulate input and output databases. GMS was developed under the direction of the U.S. Army Corps of Engineers and involved support from the Department of Defense, the Department of Energy, and the Environmental Protection Agency. Tools are provided for site characterization, model conceptualization, finite-difference grid generation, geostatistics, telescopic model refinement, and output post-processing.

The groundwater elevation data set of Graves (1991) for March of 1986 will be used to calibrate the model and the groundwater elevations collected during the study will be used to validate the model. These models will simulate steady-state conditions. Additional transient groundwater elevation data collected between 1981 and 1986 by the USGS (Graves, 1991) will be used to validate the model as well. Calibration will be achieved by adjusting aquifer properties within reasonable limits in order to match observed average groundwater levels and discharge rates. Discharges will include base flow to drainage channels which discharge to the Bahía de Boquerón and Bahía de Guánica. These data will be obtained from published reports for 1986 and measured during the study. We will perform the MODFLOW calibration with the assistance of a commercially available nonlinear optimization program called PEST (Doherty, 1994).

REFERENCES

Anderson, H. R., 1977. Ground water in the Lajas Valley: U.S. Geological Survey Water-Resources Investigations Report 68-76, 45 p.

Brigham Young University, 1997. Groundwater Modeling System (GMS), User's Manual, Version 2.1. Engineering Computer Graphics Laboratory.

Doherty, J. 1994. PEST Model Independent Parameter Estimation. Watermark Company.

Graves, R. P. 1991. Ground-water resources in Lajas Valley, Puerto Rico. U.S. Geological Survey Water-Resources Investigation Report 89-4182. 55 p.

Magaly Rivera, 2003. Welcome to Puerto Rico. http://welcome.topuertorico.org/city/lajas.shtml

McDonald, M. G. and A. W. Harbaugh. 1984. A Modular Three-Dimensional Finite Difference Ground-Water Flow Model. U.S. Geological Survey.

Pérez Alegría, L. 2002. Sistema de Informatión Geográfico Reserva Agrícola del Valle de Lajas. Final Report, Puerto Rico Department of Agriculture. Prepared by the University of Puerto Rico Agricultural and Biosystems Engineering Department. July 31, 2002.