Water and Hydroelectric Power Generation on Finca [-----------],
Carate, Costa Rica:  A Feasibility Study

For:  [------------]
By:  Osa Water Works, S.A.
www.osawaterworks.com
A member of the Osa Group

June 23, 2001

Introduction

         On June 21, 2001, a field survey was undertaken on the Finca [-----------], Carate, Costa Rica, by Osa Water Works, Jeff Lantz, and prospective buyers of the property (Figure 1). 

Figure 1.  Topographic map showing the approximate boundaries of Finca [-----------].

The objective of the survey was to determine the feasibility of developing water resources present on the property for water supply and hydroelectric power generation.  An additional objective of the field survey was to evaluate the existing water intake of the [----------------], which is located within the Finca [-----------] property boundaries, and to determine if it is possible to:  1) continue to both satisfy the needs of the development under consideration; and 2) provide water to the [----------------] and other subjacent property owners that have agreements from [----------------] granting them water rights.  A plano of the property is shown in Figure 2.

Water Demand

         The Finca [-----------] contains four building sites (Figure 2).  Long term plans include the development of those building sites for residential and commercial use including a restaurant/clubhouse and bungalows.  The calculation of water demand was based on the standard United States water demand assumptions of 100 gallons/day/person, and an assumption of 5 persons per household[1].  Bungalow water demands were calculated on an assumed average occupancy of 40 guests and an assumed water demand of 50 gallons per guest per day.  Restaurant water demands were calculated on the basis of an assumed daily consumption of 300 gallons.  Bungalow water demands were determined based on an assumed peak occupancy of 20 persons/day and an assumed water consumption of 50 gallons per day per person.  The water demand calculations of the property in question are summarized in Table 1.

Table 1.  Summary of Water Demands for the Development Project.

         Based on these assumptions, the total water demand of the property in question is 5,300 gallons per day, which is equivalent to 3.68 gallons per minute (gpm).  In the absence of additional hookups and based on the assumptions given above, a continuous flow of 4.0 gpm is sufficient to supply the water required for the property in question.  In addition to the prospective property development, there are several additional existing property owners that have contracts with [----------------] granting them water supply from the Finca [-----------] property.  A summary of the water that has been contractually granted to these neighboring property owners is given in Table 2. 

Table 2.  Summary of daily water concessions contractually granted by [----------------] to neighboring property owners.

         The flow rate necessary to sustain the development plans of the Finca [-----------] prospective buyers and the neighbors which have contractual rights to water located on the Finca [-----------] property, therefore, is equal to 7.15 gpm.

Figure 3.  Unidentified seep

Water supply.

         The Finca [-----------] property contains one perennial stream that is fed by a variety of springs and seeps in the main channel and feeder tributaries.  Elevations of the springs and seeps examined during the field survey ranged from about 60 to about 280 feet in elevation.  Several ephemeral streams were also identified during the survey.  The survey was undertaken at a relatively dry time.  While the timing coincided with what is typically considered the rainy season, there had been no rain in the watersheds examined in the three days prior to the field survey and stream water flow consisted of base flow, that is ground water introduced to the stream in the form of springs and seeps.  Moreover, the survey team was accompanied by a long-time resident, Don Abdelí, that lives on the property and is familiar with the springs and their behavior during both the dry and wet seasons, who reported that stream flows at the time of the survey were comparable to summertime flow rates.

         A number of seeps (Figure 3) were found that contained water flows between 0.5 and 1.5 gpm each, which is enough to easily supply the needs of 1-2 houses.  There were five springs identified, however that each had a discharge of 5 gpm or more.  Each of these springs was reported by Don Abdelí to carry the same amount of water during the dry season as was observed during the field survey.  The largest spring source is located in Quebrada Amor.  This source is located a few hundred feet above where the [----------------] currently has a small spring box in service (Figure 4).  The intake structure is located where a spring with about 5 gpm flows into the existing stream flow of about 20 gpm, for a total water flow at that point of 25 gpm.  Discounting stream flow, the five springs identified during the survey comprised a total of 38 gpm. 

         A map of the property with the spring locations is given in figure 2.  A summary of the elevations of the springs is given in table 2.

Figure 4.  [----------------] Water Intake

Figure 5.  Spring 4, Quebrada Escondido

Table 2.  Springs identified during the survey of Finca [-----------].  See Figure 2 for spring locations.  

On the basis of the abundant water resources identified, OWW has concluded that the property contains the potential to both satisfy its own water demands and provide a community-based water system to its neighbors

Drinking Water Distribution Alternatives

         The elevations of the building sites being contemplated are given in Table 3.    

Table 3.  Summary of planned structures and elevations.

Comparison of the elevations of the building sites and the springs reveals that all of the homes can be supplied by gravity flow with the exception of the Hidden Plateau installations, which would necessarily require a water storage tank located at a location on the slope above the structures sufficiently high so as to provide an optimal 40 psi of water pressure.  This tank would have to be located about 90 feet above the restaurant and residence.

Due to the relatively dispersed locations of the home sites and the great difference in elevation, it is unlikely that a single water source / water distribution tank will be the optimal solution to water supply.  However, 76% of the water identified was found in springs feeding Quebrada Amor.  This is the most logical source of water for the Hidden Plateau and Fila structures, the bungalows, and all off-site residences.  It is likely that either springs 4 and/or 5 will readily supply the water demands of the Second Plateau and La Pansa residences.  However, if these sources are used, then water must be pumped up to storage tanks above the respective households.  One way to circumvent these pumping needs is to take all the drinking water from one of the three Quebrada Amor springs, pump it to a distribution tank above Hidden Plateau and gravity feed pressure diffusion tanks above the Small Plateau and La Pansa building sites.

Based on the geomorphology of the springs examined, intake structures would consist of either spring boxes designed to exclude surface water capture or infiltration galleries, which would admit both spring and surface water flow through intakes buried in stream sediment in such a manner as to provide filtration of suspended sediment and turbidity.

Hydroelectric Power Generation.

         On the basis of the stream flow observed in Quebrada Amor, it is not feasible to deploy a year-round hydroelectric power generation capacity without incurring unacceptable environmental impact.  However, the rainy season hydroelectric potential of two of the watersheds examined is very promising.  Owing to the great fluctuation in flow and the relatively small flow available, direct-AC power generation is completely out of the question.  However, a DC power generation system would provide a reliable source of power to augment the solar power that would be required during summer months.

Without knowing winter-time flows of the watersheds in question, it is impossible to specify the amount of energy that is potentially available.  However, if we assume: 1) that Quebrada Amor doubles in average flow during the rainy season; 2) that a pipeline is used that takes advantage of 160 feet of head; 3) that the generating source efficiency is 40%, and 4) that 50% of the flow is diverted for power generation, then power generation expectations are around 5.5 kW/day, enough power to sustain the energy demands of one full-size, fully equipped residence or up to 10 bungalows equipped with lights and fans.

Similarly, if Quebrada Escondido is tapped for hydro, then an additional 5.5 kW may be possible, though this would reduce the wintertime stream flow remaining in the watershed to around 5 gpm, that is, about the same as its summertime flow.  Because Quebrada Escondido is a tributary of Quebrada Amor, it is possible to use two pipelines to boost the water delivery feeding a single Pelton wheel located downstream of these two channels.  In order to capitalize on the great variation in expected flow, we propose a four-nozzle variable-flow adjustable system that can generate greater power when there is more water and that could capitalize on very low flows to generate at least some energy for the project.  Eleven kW of power is enough energy, for example to easily supply 14 well-appointed bungalows, a freezer, and a washing machine for the lower portion of the property.  As a point of comparison, in order to generate 11 kW daily using solar panels, would require 22 100-watt solar panels, based on 5 hours of daily insolation and more during the winter season.

Confirmation of winter-time hydro feasibility will necessarily involve a wet-season survey to confirm flow rates of the two target streams.

Political Considerations

One of the concerns of the prospective developers is the fact that the [----------------] presently derives its water from Quebrada Amor within the boundaries of the property under consideration.  The crude surface water intake (figure 3) is capable of withdrawing an amount of water far in excess of what the [----------------] actually needs for potable water supply, irrigation, and pool water supply.  In the absence of competing interests, [----------------] presently uses this water without any concern for water conservation, evinced by the dependence upon continual replacement of pool water and the presence of a fountain that shoots water into the air fifteen feet or so.  However, the owner of the [----------------] has grown accustomed to his water-consumption practices.  Moreover, there is a precedent in Costa Rican water law that would provide the [----------------] a legal basis for contesting any decision by the prospective owners to modify the existing intake or pipeline.  While the landowners would most likely prevail in a legal contest, given the [----------------]’s contractual entitlement to only 2000 gallons per day, this process could consume years, engender bad blood among neighbors, and effectively make development plans more difficult to realize.  Clearly, it is in the prospective owners´ best interest to convince the [----------------] to participate in whatever overall development plan is settled upon in exchange for the guarantee of sustained, high quality water supply in perpetuity.

          An additional concern are the seven subjacent residential properties that all have a need for potable water supply.  After consideration of all possible alternatives, a solution was devised that:  1)  provides the property owners with all the water they will need for their development; 2)  provides the [----------------] with a dependable source of water;  3) Inhibits the [----------------] from taking more water from their present intake than is required for potable water supply and light irrigation; and 4) employs the use of a hydraulic ram pump for water displacement, obviating the energy input requirements of an electrical pump; and 5) provides water supply for neighbors that enables recovery of up to $35,000 of the cost of system implementation.  The system under proposal is illustrated in Figure 6 and discussed in detail below.

Conceptual System Design

         The system depends entirely upon a single source of potable water.  An infiltration gallery installed at Spring 1 will feed a pipeline that charges a hydraulic ram pump a small way downstream of Terry’s present intake.  The available spring flow of 20 gpm will provide delivery of 2 gpm to the distribution tank located about 90 feet higher than the structure to be built on Hidden Plateau.  The remaining 18 gpm will charge the distribution tank adjacent to the ram pump for delivery of water to La Fila, Abdelí’s house, the bungalows, and also the neighboring properties as shown in Figure 6.  Overflow from the Quebrada Amor storage/distribution tank will be returned to the stream.

         Under this scenario, the stream will be dry from the intake at Spring 1 until the [----------------] intake, which is fed by a 5 gpm spring, giving the [----------------] 5 gpm to work with  year round.  Immediately below this existing intake the overflow from the distribution tank would be returned to the stream, ensuring a year round flow of at least 15 gpm at the driest time of the year and assuming full utilization by downstream users.  This guarantees that the stream will never be depleted of water due to potable water withdrawals.  Most importantly, it ensures that the [----------------] will never be able to dry out the creek to satisfy the indiscriminate water usage to which it is presently accustomed.

         The two gpm water delivery to the top of Hidden Plateau is enough flow to satisfy the water needs of 29 full time residents assuming the very liberal stateside standard for water demand calculations of 100 gallons per person per day.  In order to ensure that all downstream residences and businesses (Hidden Plateau, Second Plateau, and La Pansa) have adequate water during peak demands, the storage tank should be designed for a capacity of not less that 10,000 gallons.

         Water from the Hidden Plateau tank will be delivered by gravity feed to two considerably smaller pressure diffusion tanks located in series in order to provide the lower elevation Small Plateau and La Pansa building sites with optimal domestic water pressure.   

Neighboring homeowners (as well as lower elevation Finca Amor structures) can all be supplied water from the Quebrada Amor water collection tank.  A pipeline would carry this water down the stream and then along the road.  Homeowners in the area would then have the option of tapping into the pipeline for $4-5000 hookup cost.  Metering of the water usage will provide a means of ensuring that these users do not exceed a monthly water usage quota to be established as part of a set of system operational guidelines.  Since there are seven property owners (other than the [----------------]) that need water now or will in the near future, this represents $28-35,000 toward offsetting the capital costs of installation.

While there is enough water during dry conditions to sustain a modest hydroelectric generation potential, exploitation of this resource would require all but drying up the creek during summer months from the proposed intake all the way to the proposed generation station at Don Abdelí’s house.  OWW considers this to constitute an excessive environmental impact.  However, a winter-time hydroelectric system is entirely reasonable and can be implemented at a negligible impact to the environment.  As previously mentioned this will require a winter-time survey of water flows to specify the upper range of wattage that can be generated.  We are confident based on the survey undertaken, discussion with Don Abdelí and our experience, that a minimum of 11 kW daily can be generated  throughout six months of the year.

The proposed hydroelectric system consists of two 2” pipelines on Quebrada Amor and Quebrada Escondido as shown in Figure 6.  These pipelines would join at the confluence of the two streams, and a three inch pipeline would carry the water to the proposed generation point at Don Abdelí’s house.  The deployment of a four nozzle manifold would enable power generation to be optimized according to the flow in the stream and through the use of valves.  In this manner,  the generation system would have the flexibility to supply power in the range of 5 kW/ day – 25 kW/day, the former during dryer times and the latter during storm runoff.

Additional Needs

         Before a formal cost estimate can be prepared, additional work is necessary.  This work and associated costs is summarized below.

1)  Winter-time hydro survey, system design and engineering        $ 1,000

2)  Water quality analysis                                                              $   400

TOTAL                                                                                            $1,400

         The final design and engineering will provide the final details of such other information necessary to detail costs as: 1)  pipeline lengths;  2) number and size of distribution and pressure diffusion tanks; 3) pump sizes; 3) filtration requirements; and 4) Pelton generator size and configuration. 

Final Recommendations

         There is unquestionably enough water on the Finca Amor property to supply the prospective owners with all the water necessary for all the project elements being planned.  Moreover, there is enough water to continue to supply [----------------] with all the water necessary for its reasonable potable water consumption, and there is enough water to supply up to 10 neighboring properties with residential water supply with modest irrigation.  There is enough water that after supplying all those needs, the drop in water flow in the stream will not even be noticeable.

         There is not enough water during the dry season to generate hydroelectric power without incurring an unacceptable environmental impact.  However, during winter months, the owners can expect a sustained hydroelectric power generation of 11 kW per day.

         Perhaps the most attractive incentive of the comprehensive solution proposed in this document is an avenue to finance a substantial portion of the costs with hookups to downstream neighbors that need a dependable domestic water supply for their residences and at the same time provide goodwill among neighbors by supplying the invaluable resource of water.

         Should the purchase of the property proceed and should the new owners elect to proceed with engineering and design, OWW recommends that the Osa Group approach the other owners about buying into the system.  These neighbors are all friends of the three OWW principals and most are clients of one or more of the five Osa Group companies.

         Unless the prospective owners would like to move faster, a reasonable time frame for completion of winter time hydro survey and design and engineering of the system appears to be in October at the time of the closing of the property purchase should the prospective owners decide to buy the property.  Under this time frame, construction could proceed at any time thereafter.

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