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Resumen de los datos bajos en el flujo del Ro Guacimal arriba, medidos en el Centro de Arte, Monteverde.
Summary of low flow data of the Upper Ro Guacimal, measured at the Community Arts Center, Monteverde.
g [no date].
Books / Reports / Directories
Low Water Flow Data
Resumen de datos bajos en el flujo de agua
Scanned by Monteverde Institute.
The State of Water in Monteverde, Costa Rica: A Resource Inventory.
Summary of Low Flow Data of the Upper Rio Guacimal Measured at the Community Arts Center, Monteverde Amy Rhodes Department of Geology Smith College Northampton, MA 01063 firstname.lastname@example.org Andrew Guswa Picker Engineering Program Smith College Northampton, MA 01063 email@example.com The gage station consists of a pressure transducer that measures water depths (stage) calibrated to a staff, and these depth readings are recorded to a data logger. The pressure transducer measures stage every second, and the data logger records an average stage value every 10 minutes. Please note that the stage readings are not surveyed elevations. Rather they are calibrated to a staff, or ruler, that has an arbitrary zero value. Therefore, differences in stage readings are meaningful, but the absolute values of stage are not. We constructed a rating curve (Fig. 1) that calibrates measurements of stage to spot measurements of stream flow, or discharge (volume water/time). Discharge values are calculated by integrating measurements of stream velocity over a cross-sectional area of the stream channel. The rating curve enables us to calculate discharge values for stage readings recorded by the data logger. The accuracy of the rating curve is limited by the highest and lowest flow measurements, and the rating curve is not calibrated for the times of lowest flow of the stream. The lower boundary of the rating curve occurs at 0.26 feet (0.079 m). We measured discharge twice at this stage reading; the average discharge at this stage is 56.5 l/sec (measured values were 52.5 l/sec and 60.5 l/sec). The year 2001 represents our most complete set of data that captures the dry season of Monteverde (Fig. 2). Our stage data span from 14 Jan 6 Nov 2001. During this time, we have recorded 132 days of the dry season (14 Jan 24 May 2001). Because our rating curve is not calibrated to low flows, we cannot confidently report an average flow during the dry season. However, we can say that the flow of the upper Guacimal was at or below 56.6 l/sec for 84% of our measurements during the dry season Occurrence of stream flows less than 56.6 l/sec can only be estimated, and our quick estimate suggests that the average flow during the dry season is ~8 l/sec. However the error on this average value is likely to exceed the proposed withdrawal rate of 19.2 l/sec. Other comments: The catchment area draining to the point where our gage station is located may be larger than the proposed location of the irrigation pipe on the Queb. Cuecha. Therefore, a hydrograph of the Queb. Cuecha at the point of water withdrawal could reveal lower flows than those portrayed on our hydrograph. The implication is that exportation of water from the watershed at a rate of 19.2 l/sec at or upstream of our gage station could cause stretches of the Queb. Cuecha and the upper Rio Guacimal to go dry for a significant portion of the dry season. Conversely, if irrigated water is applied within
the watershed of the Queb. Cuecha, then a portion of the irrigated water will return to the stream. More accurate readings under low flow conditions could be achieved by installing a vnotch weir in the stream channel. This would eliminate the need for creating a rating curve and reduce difficulties associated with measuring discharge under low flow conditions. Figure 1: Rating curve used to calculate discharge of the upper Rio Guacimal. Rating curve is constrained for discharge values between 56.6 l/sec to 816 l/sec.
-500 0 500 1000 1500 2000 2500 3000 3500 Jan/1 Mar/1 May/1 Jul/1 Sep/1 Nov/1 Jan/1 0 50 100 150 200 250 300 350 Hydrograph of the Upper Rio Guacimal Discharge (l/sec) Calendar Day 2001 Julian Day Dry Season 56.6 l/sec Upper limit of Rating Curve Figure 2: Hydrograph of the Upper Rio Guacimal for 2001. Horizontal lines show upper and lower confidence limits on calculated discharge values constrained by the rating curve. Eighty-four (84%) percent of discharge values fall below the lower bounds (56.6 l/sec) of the rating curve during the dry season. Duration of dry season was interpreted until the observed, rapid rise in discharge on 28 May. Note that flow values below 0.0 l/sec did not actually occur, and the Rio Guacimal did not go dry during the time of measurement. Values below 0 l/sec are due to the poor calibration of the rating curve under low flow conditions.