Work Sample: Matapalo, Costa Rica

Hydrological Resources of Finca [---------------]
Matapalo, Osa Peninsula, Costa Rica

In the year 2000, Osa Water Works undertook field surveys to identify viable sources of potable water for property that had been recently purchased by Derek Ferguson on Cape Matapalo, Costa Rica. On the basis of recommendations made at that time, a well was dug on an adjacent property and developed. The water quality was evaluated and reported on in a preceding report.

In the interim, an additional adjoining property is in the process of being acquired, one which contains significant hydrological resources. Due to the substantial water and energy demands of the house under construction on the original property as well as the existing residence and hotel on the soon-to-be-purchased property, a field investigation was undertaken to determine the magnitude of existing resources for both water supply and hydroelectric power generation. In addition, this field survey was necessary to determine the state of existing infrastructure, including wells, intake structures, storage tanks, and pipelines to determine what steps are necessary to optimize the use of existing natural resources without compromising the environmental integrity of the pristine rain forest contained on the tract of land.

Resources Overview

Figure 1 is a map showing the boundaries and features of the now united tract of property, which for the purposes of this report has been assigned the name of Finca Manhattan. Figure 1 illustrates the water and energy infrastructure present on the property as well as a schematic of the proposed hydro pipeline, which is shown in blue. These include two wells, one spring water intake, one surface water intake, and one diesel generator.

Water quality characterization of the well dug in February and March, 2000, reveal that the well contained 93 colonies / 100 ml of fecal coliform bacteria, meaning that this water must not be ingested without first treating this water through a filtration system. Bacteriological retesting was undertaken on the most recent field survey, and those findings will be reported in a subsequent report. Pump tests of this well revealed a yield of approximately ½ gallon per minute, enough water to supply the needs of seven full-time residents provided a suitable water storage tank (1000 gallons or so) is used.

During the current survey the pre-existing well located near the road was evaluated for yield and for water quality. Under the prevailing hydrological conditions (i.e. wet season), the well is capable of sustaining a continual withdrawal of about 5 gpm. Water quality data from this well will be reported in a subsequent report.

Figure 1. Location of the property under study and the energy and water resources contained on that property.

The energy demands of the existing hotel are satisfied at present through the use of a diesel generator. A solar system has been acquired to provide for additional energy demands of the house under construction.

The stream that currently feeds the swimming pool of Bahía Esmeralda (BE) is fed by two streams that converge 447 feet upstream of the swimming pool. For the purposes of this report these two streams have been named the Left Fork and Right Fork, respectively.

The water supply for the watchman’s house is obtained directly from the river channel of the Left Fork at the location identified in Figure 1 as Left Fork Intake. The existing pipeline is polyethylene tubing, has a piping run of 1,600 feet and a total vertical relief of 250 ft.

The water supply for the main house of Bahía Esmeralda is derived from a spring located in the Right Fork (location number 3 in figure 1). The piping run is one of 592 feet across a vertical drop of 67 feet, yielding a water pressure of 29 psi at the ground level of the house. In addition to supplying water for BE, this spring also supplies water for Encanta La Vida, a neighboring lodge owned by Brian Daily. The permission for use of this water has been in place for eight years and under Costa Rican law is irrevocable. Since there are two pipelines connected to the spring and there is additional overflow around the intakes, it was not possible to quantify the spring’s flow rate. However, on the basis of our experience, the spring is a significant one by regional standards and is likely large enough to supply all the properties involved with reasonable potable water usage without compromising the integrity of the watershed ecosystem. For all the properties to use this source for irrigation and pool water, however, would almost certainly tax the ecosystem during the dry season to an unacceptable degree of environmental consequence.

A water quality sample was taken from this spring and the results will be discussed in a subsequent report.

Hydroelectric Power Generation Potential

In order to determine the adaptability of existing hydrological resources for hydroelectric power generation, a comprehensive field survey was undertaken on October 13, 2001 on the two forks of the stream that passes through Finca Manhattan immediately to the south of the BE main house. Figures 2 and 3 are representations of the channel profiles of the Left and Right Fork, respectively.

Figure 3 reveals that the river profile maintains a nearly constant gradient from the base of the waterfall all the way to the coastline. One implication is that there is no real advantage in terms of potential energy to design a system in any particular part of the river stream. Energetically, there are no diminishing returns in extending a hydro-pipeline all the way to the coastline. Therefore, the design of a hydro-generation installation has no real topographic constraints beyond the ownership boundaries of the property containing the resources.

There are hydrological constraints, but these cannot be comprehensively characterized until such a time as a dry season survey of the same watershed is completed. From our past experience with these same streams, OWW expects minimal hydro potential from January – April, and we present a proposed design that favors optimization of wet-season hydro potential while maintaining the ability to generate reduced kilo-wattage during the dry summer months.

In order to maximize the hydroelectric potential of the two surveyed watersheds, hydro pipelines are proposed in both the Left and Right forks of the stream surveyed. Both pipeline intake structures would be located at the (0,0) coordinates on the profiles of Figures 2 and 3 (Locations 1 and 2 in Figure 1). These two pipelines would be T-ed at the confluence of the two streams, and a single pipeline would convey the water from the confluence to the approximate location of Oscar’s house, where a power bodega would be constructed for power generation, battery charging, and subsequent AC inversion (Location 4 in Figure 1).

Since considerably more water is available during the wet season (winter) than the dry season (summer), the power generation potential will vary seasonally. Seasonal power generation expectations are summarized in Table 1. The calculations were based on the ability to withdraw a sustained 75 gpm from both the Left and Right Fork intakes during winter months and a sustained 10 gpm in the summertime only from the Left Fork, with the assumption that the Right Fork will be

Figure 2. Channel profile of the Left Fork through the confluence to the location of the generator housing.

Figure 3. Channel profile of Right Fork from the large waterfall to the beach.

dry at that time of the year. The winter time expectations appear reasonable as considerable times the target flow was observed at the intake points during the field survey, undertaken on a day preceded by several with only very light rainfall.

	Above Generator
	Winter	Summer
Pipeline Distance (ft)	2246
Head (ft)	LF: 249	RF: 207
Power (kW/day)	74.1	5.4

The ability to produce 60+ kW/day of power in such a short pipeline distance (2246 feet) represents a cost/benefits equation in the beneficiary’s favor. When the potential energy source is considered in light of the fact that a solar system has already been purchased and that much of the high-dollar electronics and batteries required for the system under consideration are already owned, the economics become child’s play: the two watersheds represent an energetic windfall with a nominal capital price-tag. In the wintertime, when a solar power generation system is conspired against by nature, the hydro rocks. And when the sun is king and hydro is licking its wounds, the solar system is keeping everything running. The exclusive capacities of the two systems combined with the enormous overlap of operating conditions creates an energetic capacity and built-in redundancy that can be capitalized upon to great benefit and in complete independence, though two seldom-used, high capacity diesel generators (already owned) provide for the final fail-safe guarantor of an uninterruptible power supply.

Environmental Considerations

Water is a critical component of the tropical rain forest. Removal of water from ecosystems in general and tropical ecosystems in particular, represents a change to the balance of the water budget, a factor that must be considered to rationally understand the actual impacts that human decisions have on species of plants and animals that do not have the same high-browed freedom of such choices. Cape Matapalo is volcanic terrain that knows both the poles of hydrology—wet and dry—though in different measures. During the prevalent hydrologic state of “wet”, which occurs between the months of May and November, there is such a large volume of water that courses through these watersheds that no amount of removal can impact the environment in any way. Tens of millions times more water than is proposed for this study are discharged to the benefit of no living creature into the gulf during any given rainy season. Ironically, during the summertime months the water that issues from springs in mountain stream channels is rapidly sucked through the stream sediment and faulted bedrock into subsurface aquifers. Oftentimes a visible summertime spring will wet the bed of a channel for a distance of less than 10 feet before it is lost to the subsurface. This water is lost to the ecosystem as a result, since it plays a nominal role in down-gradient ground water levels and no role whatsoever in the mountainous forest ecosystem. While such a spring during summer months may wet only a ten foot section of river bed, it is a ten foot section of river bed with water available for wildlife to drink from. The withdrawal of water for summertime diminished hydro production would remove much of that source, reducing the amount of water available in that one spot for wildlife to drink from.

While water must be “removed” from sections of a watershed in order to capitalize on the potential energy present in water flowing across significant relief, the water is ultimately returned to the stream unchanged in any way immediately beneath the Pelton wheel location. There is no real removal. However there is a diversion of water that is required to generate energy. While the Right Fork is an undisturbed natural watershed where the concern of removing water is a valid one, the Left Fork is heavily impacted by landslide scarring and large deposits of colluvial fill in the stream channel. In other words, the ecosystem of the Left Fork has already been heavily impacted by slope failure. Except during the wettest times, water carried in the left fork sinks into the colluvial deposit and is lost to the surface environment. The Right Fork, on the other hand, contains the large spring which has a discharge large enough to both provide potable water to Finca Manhattan and sustain river levels, provided the resource is correctly managed. Owing to the behavior of water in the left fork, its diversion for hydro power above the landslide scarring is not unreasonable since that water sinks into the subsurface naturally just beneath the site that is proposed for a hydro pipeline intake.

Potable, Pool, and Irrigation Water Supply

The spring discharging into the Right Fork—from which BE and Encanta La Vida currently derive their drinking water supply—has a relatively large discharge in comparison to other springs in the Matapalo area. We were unable to measure the discharge due to the obstruction of the large concrete spring box and the undesirable mixing of stream water inside the spring box. However, this source has for years provided “potable” water to two lodges with an overflow that feeds the stream (Encanta La Vida has experienced outbreaks of gastro-enteritis among its guests on occasion, confirming that this water is not truly potable without additional filtration or disinfection). The existing intake is rudimentary and allows for the mixing of surface and spring water, which unfortunately allows the normally pure spring water to be compromised by the nearly always contaminated surface stream water. This water source is located above the house under construction, meaning that water can be delivered from the spring to the house by gravity. There is not enough head (vertical relief, translating into delivery pressure) however, for the water to be distributed inside the house with sufficient operating pressure. Therefore, it will be necessary to employ a pressure tank and pump to distribute water at 40 psi throughout the house. The pressure tank and pump already planned for pressurizing the water from the storage tank at the base of the house can readily be adapted to pressurize either the spring water, or the house storage water, depending on the water management demands of the property at any given moment or time. The large storage capacity of the rain fall captation tank provides a water supply redundancy that ensures that there is always a supply of water, even if the spring water line is down for maintenance or if the owner simply wishes to reduce withdrawals from this source for environmental reasons.

Bahía Esmeralda, facilities, on the other hand, are located 95 feet below the spring, corresponding to a pressure of about 41 psi, ideal for a house. While no gastric illnesses are known by the authors to have resulted from ingestion of this water, it comes from the same source as Encanta La Vida’s water and should not be considered potable without filtration and/or disinfection.

In order to ensure water quality, it will be necessary to modify the intake structure significantly. While it might be possible to adapt the existing spring box, it may be best for many reasons—not the least of which would be to remove the environmental blemish represented by the unnatural structure—to demolish the tank and construct a much smaller and more efficient spring box that completely isolates the spring water from the stream water.

Because of the high discharge of the Right Fork spring, there is little reason to consider additional use of the well that was dug in March 2001, since it has a low yield and is of questionable water quality.

Although there is a large amount of water from the spring, it is not likely to support irrigation efforts during the dry season. Therefore, it is proposed that the most environmentally responsible alternative is to tap the presently unused resource of the downhill well. Since this well is on a low part of the property, use of this water will require a pump to transfer the water to the 35,000 storage tank that is the base of the house under construction. This, while representing an avoidable cost will enable the large flows of unused spring water to maintain creek levels, particularly if modest summer-hydro withdrawals are being made in other parts of the watershed.

Depending on the results of water analyses currently underway, it may be possible to design a potable water supply without any form of treatment, owing to the intrinsic cleanness of most spring sources. However no surface water sources are ever safe. Unless the spring intake structure is re-built, the water supply must be treated through a minimum of filtration and ideally an additional disinfection step to ensure that all naturally occurring pathogens are deactivated.

Conclusions and Recommendations

Finca Manhattan is blessed with an abundance of year-round water of high quality as well as a useable well at the lower elevations of the property. The mountain spring is located a short distance above Bahia Esmeralda and at the approximate elevation of the house currently under construction. There is expected to be enough water from these various sources in addition to the rain water captured and stored in the house under construction to provide for domestic water supply and pool filling for both the Ferguson home and the current operations at Bahía Esmeralda.

Finca Manhattan has the natural resources to provide for wintertime hydroelectric power generation potential in quantities sufficient to power several large and well-anointed American-style homes. In this particular case, with much of the basic equipment already acquired for a previously planned solar power generation system, the economics of tapping this available energy for both projects are clearly in the owner’s favor.

A summary of all of the elements of the recommended installations is provided below. Upon the purchase of Bahía Esmeralda, OWW is prepared to do a detailed engineering and design and provide the owner with a bid for the installation and commissioning of the system.