The southern zone of Puerto Rico has various independent alluvial aquifers: Patillas to Salinas, Coamo (Santa Isabel and Coamo), Juana Díaz to Ponce, Tallaboa (Peñuelas) to Guayanilla, Yauco and Guánica. The following is a description of the state of the aquifers of the southern zone.

Salinas to Patillas Aquifer

The Patillas to Salinas alluvial aquifer extends from the Grande de Patillas River to the Nigua River in Salinas, covering an area of approximately 67 square miles. The hydrological conditions are based on data from 1972, 1976, 1986 and estimates from 2000.

All of the recharge of the Salinas to Patillas aquifer comes from rain water, overflow and percolation from rivers and streams and from agricultural irrigation, which accounts for approximately 30 percent of the net amount applied. The hydrological balance in 2000 shows a recharge of 19.1 mgd from rain water. This aquifer also receives 5.7 mgd of recharge from the rivers, streams and irrigation canals and 11 mgd from infiltration of agricultural irrigation, including infiltration from septic tanks and flows not from rain.

The total discharge of the aquifer consists of evapotranspiration, the extraction of underground water and discharge into the sea. Evapotranspiration amounts to 4.5 mgd. Extraction of underground water rose to 25 mgd in 2000 and discharge to the sea is estimated to be 4.7 mgd. The hydrological data on the aquifer in this zone suggest that there is a small surplus of water of approximately 2.4 mgd. This is due to the recharging from an artificial water source in the Guayama area, the Melanía Reservoir, which provides the aquifer between 2 to 3 mgd, which is a significant amount and is comparable with the estimates of additional extraction.

Santa Isabel-Coamo Aquifer

This aquifer extends from the Descalabrado River in Coamo to the Jueyes River in Santa Isabel. It covers an area of approximately 50 square miles. The hydrological data on the aquifer in this zone include information from 1930 (pre-development), 1966-1968, 1987 and estimates from 2000.

The most recent estimates of flow from this alluvial aquifer show that in 2000 there was an annual deficit of approximately 30 mgd in the aquifer, the result of an average decrease of 13 feet in the water level of the aquifer during the period from 1987 to 2000 (13 years). The total recharge of the Santa Isabel to Coamo Aquifer comes from rain water, overflow and percolation from rivers and streams and from agricultural irrigation, which represents approximately 30 percent of the net amount applied. In 2000, the hydrological balance showed a recharge of 11.2 mgd for the aquifer from rain water. This aquifer also receives 5.5 mgd in recharge from water from rivers, streams and irrigation canals and 9.5 mgd that filters in from the agricultural irrigation, including infiltration from septic tanks and flows not from rain.

Evapotranspiration amounts to 1.3 mgd. Extraction of underground water reached 20.5 mgd during 2000 and discharge to the sea is estimated at 3.0 mgd. In 2000, this aquifer was in a state of disequilibrium and the levels of the aquifer dropped nearly 20 feet between 1996 and 2000. The hydrological data on the aquifer in this zone suggests that over-exploitation of the aquifer is estimated at 6.0 mgd. This aquifer was over-exploited even more in 1986 when 25 mgd were extracted (an over-exploitation of 11 mgd). This excessive extraction led to deterioration in the quality of the underground water in this period.

Juana Díaz to Ponce Aquifer

The alluvial aquifer in the Juana Díaz to Ponce zone covers an area of approximately 58 square miles. The hydrological data on the aquifer in this zone are not recent, reflecting conditions during the period of 1964-1965, and estimates for 2000.

The total recharge of the Juana Díaz to Ponce Aquifer comes from rain water, overflow and percolation from rivers and streams and from agricultural irrigation, which represents approximately 30 percent of the net amount applied. In 2000, the hydrological balance showed recharge of 12 mgd for the aquifer from rain water. The aquifer also receives 1.6 mgd that filters in from the agricultural irrigation, including infiltration from septic tanks and flows not from rain.

Evapotranspiration amounts to 2.5 mgd. Extractions of underground water were 7.9 mgd in 2000 and discharge into the sea was estimated at 4.1 mgd. In 2000, this aquifer was in a state of disequilibrium. The extraction of additional water is considered unlikely because of the increased concentration of dissolved solids in the underground water. The hydrological data on the aquifer in this zone suggests marginal exploitation. Similarly, these extraction scenarios should be considered very carefully because of the deterioration in the quality of the underground water in the past 20 years and the near total elimination of flooding irrigation systems.

Peñuelas to Guayanilla Aquifer

The Peñuelas to Guayanilla Aquifer includes the Tallaboa alluvial aquifer, which covers an area of 6.33 square miles, and the Guayanilla Aquifer, which covers 11.4 square miles. These include the Yauco River watershed (in the same municipality) and the Guayanilla River. The hydrological conditions of the Tallaboa alluvial aquifer are based on data from 1959-1960 and estimates in 2000 by the Department of Natural and Environmental Resources (DRNA, for its Spanish acronym). The most recent estimates of flow from this alluvial aquifer date to studies done by Grossman (1972). The hydrological balance of the Tallaboa Aquifer is summarized in Table 8.

The total recharge of the Santa Isabel to Coamo Aquifer comes from rain water, overflow and percolation from rivers and streams and from agricultural irrigation, which represents approximately 30 percent of the net amount applied. In 2000, the hydrological balance showed a recharge of 10 mgd from rain water. This aquifer also receives 3.6 mgd of recharge from rivers and streams.

The discharge of the Peñuelas to Guayanilla Aquifer consists of evapotranspiration, extraction of underground water and discharge into the sea. Evapotranspiration amounts to 10.8 mgd. In 2000, extraction of underground water reached 20.2 mgd and discharge into the sea was estimated at 1.2 mgd. The hydrological data on the aquifer in this zone indicates an over-exploitation of the resource. Similarly, this excessive extraction should be considered very carefully because of the deterioration in the quality of the underground water in the past 20 years in the context of little or no recharge.

Yauco Aquifer

The alluvial aquifer of Yauco consists of an area of approximately 7.0 square miles. This does not include the area of the Guayanilla River watershed, which represents an additional 5.77 square miles. The hydrological conditions are based on data from 1986 and estimates from 2000. The most recent estimates of the flow from the Yauco alluvial aquifer come from studies done by Quiñones-Aponte (1986). The hydrological balance of this aquifer is summarized in Table 8. Extractions and recharging in this aquifer appear to be in balance.

The total recharge of the Yauco aquifer comes from rain water, overflow and percolation from rivers and streams, and from agricultural irrigation, which represents approximately 20 percent of the net amount applied. The hydrological balance in 2000 shows a recharge of the aquifer of 4.5 mgd from rain water. This aquifer also receives 3.1 mgd of recharge in water from rivers and streams.

Discharge from the Yauco aquifer consists of evapotranspiration, the extraction of underground water and discharge into the sea. Evapotranspiration amounts to 2.0 mgd. Extractions of underground water were 4.5 mgd in 2000 and discharge to the sea was estimated at 0.08 mgd. The hydrological data on the aquifer in this zone indicate a condition of equilibrium, although in general the productivity of the aquifer depends to a great extent on the Yauco River and the rainfall in the higher part of the hydrographic watershed.

Guánica Aquifer

The most recent estimates of the flow from the Guánica Aquifer are based on studies done by McClymonds (1963). The aquifer covers an area of 6.69 square miles. The volumetric analysis is similar to that of Yauco and Guayanilla, except that the Loco River is controlled by the Luchetti and Loco Reservoirs. The Yahuecas and Guayo Reservoirs, on the northern slopes, contribute water to the Luchetti Reservoir through a system of tunnels. The system supplies the Lajas Valley Irrigation District through the Lajas Canal, as well as supplying AAA plants in Sabana Grande, Lajas and Guánica.

The Guánica Aquifer is fed principally by flow from the Loco Reservoir and filtration from the Lajas Valley Irrigation District canals. Between 1930 and 1970, the Guánica Aquifer produced between 5 and 15 mgd. Currently, there is no sugar cane farming so the underground water is mainly used for the public supply. The productivity of the wells has dropped substantially. This is due to the reduced irrigation and changes in the method of applying surface water to crops. The hydrological conditions of the Guánica Aquifer are similar to those of the Yauco Aquifer. Although reduced, extractions of underground water are estimated to be 5.2 mgd.

Author: María A. Juncos Gautier
Published: August 27, 2014.

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