la selva weirs - ots.ac.cr laselva... · one weir was built on the taconazo stream, ... taconazo...

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La Selva weirs

Original Date of This Document: 1 September 2011

Original Authors: David Genereux and Carlo Zanon, N.C. State University

Updated 7/25/14: David Genereux and Diana Oviedo Vargas, N.C. State University

Overview

During the first half of 1998 two sharp-crested V-notch weirs were constructed at La Selva

Biological Station to measure volumetric stream discharge (streamflow). One weir was built on

the Taconazo stream, several meters upstream of where the SUR trail (Sendero Sura) crosses the

stream; the other was built on the Arboleda stream, several meters upstream of the confluence of

this stream with the Sura stream. Construction was financed by a U.S. National Science

Foundation (NSF) grant to D. Genereux, and was completed in June 1998. Monitoring began at

both weirs on 24 June 1998, and continued until an interruption in funding in May 2004.

Monitoring began again under new NSF funding in November 2005 and has continued since.

Data Collected, Monitoring Equipment At each weir, an electronic shaft encoder and data logger were used to record date, time, stage

(water level in the weir pool upstream of the V-notch), and stream discharge. Data collection

frequency was 10 minutes from June 1998 through 1999, and 15 minutes beginning in 2000.

The shaft encoders were made by Enviro-Systems of Thousand Oaks, California (later acquired

by HydroLynx Systems of West Sacramento, California). Shaft encoder models SE-105S and

SE-107 were used. Resolution was 400 increments per shaft revolution (which, with a pulley 1

foot in circumference, translated to a resolution in stage measurements of 304.8 mm divided by

400, or 0.762 mm). A CS410 shaft encoder from Campbell Scientific (Logan, Utah) went into

use at the Arboleda weir on 13 March 2011. This was replaced by a SE105 in June 2012. Data

loggers from Campbell Scientific were used to collect and store data (CR10, then CR10X, then

CR510, with a CR800 going into use at the Arboleda on 8 January 2012 while a CR510 was still

in use on the Taconazo).

The shaft encoders employed a steel tape that rested on a pulley 1 ft in circumference; a large

plastic float was attached to one end of the tape, a steel counterweight to the other end. As the

float rode up and down with the changing water level in the stilling well (below), the clockwise

and counter-clockwise pulley rotations were counted and converted to stage by the data logger.

Approximately weekly, a research technician at the site downloaded data at each weir, and also

visually read and then recorded stage from a staff gauge (marked in 1 cm increments) installed

on the stilling well at each weir, as a check on the stage recorded by the data logger.

Stream discharge was calculated by programming a standard stage-discharge equation into the

data logger program at each weir. The equations, for sharp-crested V-notch weirs, were taken

from Rantz et al. (1982, p. 305):

1. Taconazo (90 degree V-notch): Q (ft3/s) = 2.47(h, ft)

2.5 (Rantz et al.), or, in the units used

in the data logger programs, Q (m3/min) = 81.82(h, m)

2.5

2. Arboleda (120 degree V-notch): Q (ft3/s) = 4.35(h, ft)

2.5 (Rantz et al.), or, in the units

used in the data logger programs, Q (m3/min) = 144(h, m)

2.5

2

where Q is stream discharge and h is stage.

Physical Infrastructure

The weir designs are based loosely on Reinhart and Pierce (1964), with adaptations to local site

conditions. Each structure consists basically of a concrete box that forms the stilling pool; the

downstream face of the box contains the sharp-crested V-notch. Thus, each structure has:

1. a “weir wall” (the wall across the stream, containing the V-notch)

2. two “side walls” (walls along the right and left streambanks, upstream of the weir wall)

3. a “floor” (the floor of the stilling pool upstream of the weir wall, between the two side

walls)

4. an “apron” (a small floor on the downstream side of the weir wall, onto which the water

spills as it falls through the V-notch).

All walls were reinforced with welded steel mesh in the concrete. Total concrete use was about

60 metric tons of dry ready-mix concrete.

At each weir, the weir plate with the V-notch was fashioned from aluminum plates 11 mm thick.

A single aluminum plate with a 90 degree V-notch was used as the weir plate at the Taconazo.

The Arboleda had a much larger weir plate constructed from three separate aluminum plates (a

central plate with a 120 degree V-notch and a plate on each side that extended the V-notch from

the central plate). At each weir, the weir plate was set directly into the concrete of the weir wall.

The downstream side of the V-notch in each plate was beveled to a steep angle, and the edge of

the notch was machined to a thickness of 1 mm (i.e., the bevel was not taken all the way to the

edge of the notch, so there was not a sharp knife-edge in the notch).

At each weir, stage measurements were made inside a stilling well. Each stilling well is 10 inch

(nominal) gray PVC pipe, oriented vertically with its base set in concrete next to one of the side

walls. An instrument platform sits atop each stilling well; this platform holds the shaft encoder

and data logger, and is covered by a painted hinged box constructed of thin steel. A horizontal

catwalk made of welded steel pipe runs out to each instrument platform from the adjacent hill

slope.

There are also “drain pipes” in each weir wall. These pipes carried the streamflow during

construction of the weirs, and were closed off (by bolting blind flanges to the companion flanges

on the drain pipes) when the weirs were complete, to allow the stilling pools to fill and

eventually spill through the V-notches. The blind flanges can be removed to drain the stilling

pools if necessary for weir maintenance or repair. The dimensions below are approximate.

TACONAZO

weir wall: about 2 m long (across the stream channel) at the base, 4 m long at the top (wall

sits in an irregular space between two large boulders and is longer toward the top), 35 cm

thick, vertex of V-notch about 60 cm above floor, top of wall about 150 cm above floor,

vertical dimension of V-notch from vertex to top is 90 cm

right side wall: about 4 m long, about 30 cm thick, top about 175 cm above floor

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left side wall: about 3 m long (between two boulders), about 35 cm thick, top about 190 cm

above floor, with a deeper extension on the downstream side about 40 cm wide, 5 m long,

wrapping around one of the boulders

floor: covers an irregularly-shaped area of about 16 square meters of stream bed, thickness

from 10 to 50 cm (thick portions cover small areas dug out around large bounders and side

walls)

apron: 6 concrete sacks on downstream side of V-notch (area of about 3.5 square meters)

stilling well: PVC pipe, 10-inch (nominal) diameter, on right side wall, two small holes at

base provide hydraulic connection to stilling pool, elevation of instrument platform at top is

4.58 m above the vertex of the V-notch

drain pipe in weir wall: one steel pipe, 1 m long, 6-inch (nominal) diameter, with steel

companion flange, to which a stainless steel blind flange is bolted, rubber gasket between

flanges

ARBOLEDA

weir wall: about 4 m long, with extensions (beyond the side walls and into the streambanks)

of about 1 m on the right side and 2.5 m on the left side, about 44 cm thick, vertex of V-notch

about 70 cm above floor, top of V-notch about 190 cm above floor, vertical dimension of V-

notch from vertex to top is 122 cm

right and left side walls: about 8 m long, about 35 cm thick, top about 90 cm above floor,

with a sloping concrete layer poured on the ground on the hill slope just above the top of

each wall for further stabilization of the base of the slopes

floor: about 3.5 m wide across the stream, about 3 m long, about 15 cm thick

apron: about 3.5 m wide, about 2.5 m long, about 20 cm thick, flanked on each side by a

buttress on the weir wall

stilling well: PVC pipe, 10-inch (nominal) diameter, on left side wall, two small holes at base

provide hydraulic connection to stilling pool, elevation of instrument platform at top is 5.38

m above the vertex of the V-notch

drain pipes: four total; two PVC pipes, 10-inch (nominal) diameter, on left side of weir

wall; one PVC pipe, 10-inch (nominal) diameter and one steel pipe, 6-inch (nominal)

diameter, on right side of wall; all drain pipes about 1 m long; all pipes affixed with

companion flanges, to which blind flanges are bolted (PVC flanges for PVC pipes, steel

flanges for steel pipe), rubber gaskets between companion and blind flanges

Data Gaps, Back-flooding

Some gaps in data collection have occurred due to infrequent equipment glitches or failures, but

the cause of most gaps was occasional “back-flooding” from the Rio Puerto Viejo.

The two V-notch weirs are subject to periodic flooding by large flood waves that travel down the

Rio Puerto Viejo (the Arboleda and Taconazo streams are tributaries to the Sura stream, which in

turn is a tributary to the Puerto Viejo). These flood waves can result in stream stage at the weirs

rising 5 m or more in several hours, far above the height of the weir walls (0.9 m for the

Taconazo and 1.2 m for the Arboleda, relative to the vertexes of the V notches). We refer to this

as “back-flooding” because the flood waters come from downstream of the weirs (rather than

upstream) and cause water to back up in the Arboleda and Taconazo watersheds. Such back-

4

flooding is a normal part of the lowland hydrology in this region of Costa Rica, and is thus an

inescapable aspect of the operation of any gauging station in the area.

It is important to identify as accurately as possible periods of back-flooding in the data record, in

order to remove them from the record. Standard weir equations for V-notch weirs such as those

used at the Taconazo and Arboleda only apply to fully aerated nappes (i.e., to cases in which

water spills freely through the V-notch and falls, surrounded by air, to a tailwater elevation that

is lower than the vertex of the V-notch). If the tailwater elevation exceeds that of the vertex of

the V-notch (i.e., if back-flooding exists), the weir is at least partially submerged and in this

condition the discharge depends on the stage both upstream and downstream of the notch (and

equations like those given above, that depend only on stage upstream of the notch, will not give

accurate discharge values). Without stage monitoring on the downstream side of each V-notch,

we sought to exclude from the records any data collected during back-flooding. (In cases of

extreme back-flooding, the shaft encoder and/or data logger have been destroyed by water

damage, but in most back-floods the water level did not reach the instrument platform and the

equipment continued to collect data during the flood, requiring us to estimate the start and end

times of back-flooding and exclude from the record the data that were collected between these

times).

Most cases of back-flooding were obvious (the stage rises over the height of the weir wall, a

flood so large it could not be generated from upstream alone by local rainfall), though even in

these cases some judgment was used to estimate the time when back-flooding started and ended

(using the slopes of hydrographs and the pre-flood stage values, local rainfall data, and

comparison between data at the two weirs). Cases of smaller back-flooding (< 1 m) could be

difficult to identify, though even in these cases local rainfall data from La Selva Biological

Station was useful (e.g., if stage rises to 50 cm at a time when there is little or no local rainfall,

the cause is most likely a small back-flooding event).

Also, comparison of peak stages at the Arboleda and Taconazo during a large back-flooding

event, at a time when the water surface between the two weirs (in the Sura) should have been

relatively flat (because the flood wave was turning from incoming to outgoing at its peak),

suggests that the Arboleda weir is about 1.2 m lower in elevation than the Taconazo weir

(comparing the vertexes of their V-notches). This suggests there can not be back-flooding at the

Taconazo unless the stage at the Arboleda is about 1.2 m (clearly back-flooded, to the top of the

Arboleda V-notch). Thus, even small back-flooding at the Taconazo should be obvious from

stage records at the Arboleda (a stage of 1.2 m at the Arboleda means the tailwater at the

Taconazo has just about reached the vertex of the Taconazo V-notch). Also, when it occurs,

back-flooding must start sooner and end later at the Arboleda weir than at the Taconazo weir

because of the lower elevation of the Arboleda (and again, the start and end times at the

Taconazo are constrained by the stage measurements at the Arboleda).

Tables found below after the weir photographs list the gaps identified during 2006-2010 at each

weir.

In order to provide a continuous discharge record, we estimated stream discharge during the gaps

in observations (i.e., we “filled” the gaps), using two approaches:

5

1. For gaps during which there was no rainfall recorded at La Selva Biological Station, we

used linear interpolation: interpolating linearly from the last reliable data point before the

gap to the first reliable data point after the gap, we estimated the discharge at 15 minute

intervals during the gap.

2. For gaps during which there was recorded rainfall at La Selva, we filled the gap with

discharge simulated using the computer hydrologic model TOPMODEL, as described in

Zanon (2011) and Zanon et al. (2014). The model was run with a 30-minute time step (to

match the available precipitation data), so the resolution of these “gap fills” was lower

than the 15-minute resolution of the measurements.

In the data tables, the discharge values from these gap fills are reported in a separate column

from the measured discharge values, to help distinguish the measurements from the gap fills.

Use of Data, Acknowledgment

The data are openly available for scientific use. Publications reporting the data, or conclusions

or results based on the data, should acknowledge financial support for construction of the weirs

(U.S. National Science Foundation (NSF) award EAR-9800129), and subsequent data collection

(NSF awards EAR-9903243, EAR-0049047, EAR-0439732, and EAR-0421178, and U.S.

Department of Energy award DE-SC0006703). The principal investigator (PI) overseeing the

weirs welcomes discussions regarding collaborative use of the data in publications or other

efforts. D. Genereux was the PI on 5 of the 6 awards listed above and a co-PI on EAR-0421178

(Steven Oberbauer, Florida International University, was the PI of that award).

Principal Investigator

David Genereux, Ph.D.

Professor

Dept. of Marine, Earth,& Atmospheric Sciences

Jordan Hall, Room 5135

North Carolina State University

Raleigh, NC 27695-8208 USA

phone: 919-515-6017 fax: 919-515-7802

e-mail: [email protected]

References

Rantz, S.E., and others. 1982. Measurement and Computation of Streamflow (2 Volumes), U.S.

Geological Survey Water Supply Paper 2175, 631 pages.

Reinhart, K.G., and R.S. Pierce. 1964. Stream-Gaging Stations for Research on Small

Watersheds. Agriculture Handbook No. 268, Northeastern Forest Experiment Station,

Forest Service, U.S. Department of Agriculture, 37 pages.

Zanon, Carlo. 2011. Watershed hydrologic modeling to assess interbasin groundwater flow in a

tropical rainforest. M.S. Thesis, Department of Marine, Earth, and Atmospheric Sciences,

North Carolina State University, Raleigh, NC, 225 pages.

http://repository.lib.ncsu.edu/ir/handle/1840.16/6738

Zanon, C., D.P. Genereux, and S.F. Oberbauer. 2014. Use of a watershed hydrologic model to

estimate interbasin groundwater flow in a Costa Rican rainforest. Hydrological

Processes, 28: 3670-3680. doi: 10.1002/hyp.9917.

http://repository.lib.ncsu.edu/ir/handle/1840.16/6738

6

Photographs of the Weirs

Figure 1. Looking upstream at the Arboleda weir. The gray PVC stilling well, topped by the

white instrument enclosure, is to the right. The steel catwalk leads to the instrument enclosure.

The top of the staff gauge (white with black markings), bolted to the bright green upright of the

catwalk, is visible over the weir wall. Blind flanges (white with darker stains) on two of the

drain pipes are partially visible above the water line. November 2001.

7

Figure 2. A worker on the concrete apron of the Arboleda weir. February 2000.

Figure 3. The Arboleda weir. July 2002.

8

Figure 4. Graduate student researcher (Michael Jordan) on the Arboleda catwalk with an Isco

automated water sampler. July 2002.

Figure 5. The Taconazo weir. A steel catwalk runs from the hillside on the left out to the gray

PVC stilling well with white instrument enclosure on top. A staff gauge (white with black

markings) is bolted to the lower part of the stilling well. July 2002.

9

Figure 6. Taconazo weir. The steel drain pipe through the weir wall (lower right) is closed off

with a steel blind flange. The weir wall lies between two large natural boulders. July 2002.

Figure 7. Instrument platform and enclosure at the Taconazo, showing the shaft encoder (center)

and the white fiberglass box (right) holding the data logger and 12 volt battery. July 2002.

10

Gaps in Discharge Data, by Watershed and Year

E: data recorded but excluded

NR: nothing recorded

E, NR: some of both

M: the gap was filled with TOPMODEL simulated discharge

S: the gap was filled with a straight line (linear interpolation)

C: data recorded and corrected (this is not considered a data gap, just a correction to raw

stage values, thus it is noted but not included in the total gap time).

Arboleda gaps 2006 Taconazo gaps 2006

start day,

time

end day,

time

days

E/NR

Gap

Fill

start day,

time

end day,

time

days

E/NR

Gap

Fill

15, 0330 15, 1945 0.7 E M 15, 1000 33, 1500 18.1 E M

15, 2000 20, 1515 4.8 E, NR M 138, 1000 138, 1415 0.2 E S

28, 0830 29, 1645 1.3 E M 156, 1845 159, 1345 2.8 NR M

31, 1900 33, 0315 1.3 E M 179, 0315 179, 2145 0.8 E M

89, 1230 90, 2330 1.5 E M 180, 1400 187, 1415 7.0 E,NR M

179, 0215 186, 1645 7.6 E M 194, 1800 196, 1615 1.9 E M

194, 1300 196, 1630 2.2 E M 198, 2000 199, 1300 0.7 E M

198, 1215 200, 1115 2.0 E M 261, 2045 262, 0130 0.2 E S

261, 2015 263, 1800 1.9 E M 305, 2030 306, 0000 0.2 E S

282, 1930 283, 1115 0.7 E M

322, 1645 323, 0745 0.6 E M

340, 1930 341, 0000 0.2 NR S

TOTAL 24.8 TOTAL 31.9


start day,

time

end day,

time

days

E/NR

Gap

Fill

start day,

time

end day,

time

days

E/NR

Gap

Fill

186, 0000 187, 2030 1.9 E M 186, 0630 187, 1545 1.4 E M

190, 1845 191, 0730 0.5 E S 190, 1945 190, 2300 0.1 E S

200, 1830 202, 1500 1.9 E M 200, 1830 202, 1430 1.8 E M

234, 0215 234, 0600 0.2 E S 220, 0915 223, 0930 3.0 E M

252, 2000 253, 1230 0.7 E S 252, 2100 253, 0230 0.2 E S

310, 2315 314, 0930 3.4 E M 310, 2345 313, 1115 2.5 E M

320, 1600 322, 1645 2.0 E M 321, 0215 324, 0445 3.1 E M

324, 1245 325, 1500 1.1 E M 324, 1230 325, 1130 1.0 E M

359, 0430 360, 2315 1.8 E M 359, 0745 360, 1115 1.2 E M


11


start day,

time

end day,

time

days

E/NR

Gap

Fill

start day,

time

end day,

time

days

E/NR

Gap

Fill

3, 0500 5, 1515 2.4 E M 3, 0945 4, 1815 1.4 E M

108, 1200 108, 1845 0.3 E S 220, 1015 220, 1930 0.4 E S

142, 1600 143, 1530 0.0 E - 286, 2030 287, 0100 0.2 E S

166, 0500 166, 1545 0.5 E M 323, 1200 324, 1600 1.2 E M

220, 0700 221, 0500 0.9 E M 327, 0615 346, 1015 19.2 E, NR M

225, 2315 226, 0430 0.2 E S 348, 2215 349, 1730 0.8 E M

286, 1600 287, 0930 0.7 E M 361, 1045 362, 1200 1.1 E M

306, 2230 307, 1630 0.6 E M

323, 1015 325, 0900 2.0 E M

327, 0445 346, 0930 19.2 E, NR M

348, 2115 349, 1300 0.7 E M

361, 1015 362, 1200 1.1 E M



start day,

time

end day,

time

days

E/NR

Gap

Fill

start day,

time

end day,

time

days

E/NR

Gap

Fill

25, 1245 25, 2000 0.3 E M 35, 1500 39, 0445 3.6 E M

28, 0930 28, 1900 0.4 E,NR M 64, 1900 65, 1200 0.7 E M

35, 0230 39, 1500 4.5 E M 65, 1700 65, 2300 0.3 E M

64, 1645 66, 0445 1.5 E M 67, 2230 68, 0400 0.2 E M

67, 2030 68, 0930 0.5 E M 199, 1300 201, 0515 1.7 E M

115, 1315 115, 1330 0.0 NR - 202, 1945 203, 0915 0.6 E M

132, 1145 132, 2045 0.4 E M 216, 1400 217, 0530 0.7 E M

135, 1000 137, 1330 2.5 E S 317, 0115 317, 0945 0.4 E S

175, 2045 176, 0400 0.3 E S 320, 2315 321, 0645 0.3 E M

186, 1000 187, 0045 0.6 E S

191, 0300 191, 0400 0.0 E S

199, 1300 201, 0445 1.7 E M

202, 1945 205, 0045 2.2 E M

216, 1015 218, 1330 2.1 E M

285, 1215 289, 1330 4.1 E M

304, 1330 308, 0945 3.8 NR M

310, 0615 310, 1000 0.2 NR S

310, 1845 311, 1315 0.8 NR S

311, 1515 312, 1300 0.9 NR S

312, 1430 313, 1715 1.1 NR M

317, 0045 318, 0530 1.2 E M

320, 2130 321, 1615 0.8 E M

348, 0900 348, 1745 0.3 E M

359, 1345 365, 2345 6.4 NR M


12


start day,

time

end day,

time

days

E/NR

Gap

Fill

start day,

time

end day,

time

days

E/NR

Gap

Fill

1, 0000 6, 1215 6.5 NR M 10, 2030 14, 0700 3.4 E M

7, 0300 7, 0830 0.2 E S 43, 1045 58, 1545 15.2 E M

10, 1730 16, 1430 5.9 E M 63, 0100 63, 1030 0.4 E M

48, 1745 49, 0430 0.4 E M 81, 2200 82, 2230 1.0 E M

49, 1945 51, 1345 1.8 E M 163, 2045 164, 0215 0.2 E S

52, 0000 56, 0845 4.4 E S 166, 1915 166, 2245 0.2 E S

56, 1745 57, 1330 0.9 E M 171, 2045 172, 0430 0.3 E M

57, 1345 64, 1500 7.0 NR M 172, 2130 173, 0815 0.5 E S

65, 1045 71,1530 6.2 E M 293, 2115 294, 0315 0.3 E M

81, 2130 85, 1600 3.7 E M 330,1300 339, 1415 9.1 NR M

163, 1900 164, 0630 0.4 E M 339, 1430 346, 1500 7.0 E M

166, 1515 167, 0545 0.6 E S 346, 1515 356, 1530 10.0 NR M

171, 2015 173, 1730 1.9 E M 361, 900 362, 2300 1.6 C C

177, 1345 187, 1500 10.1 NR M 362, 2315 363, 1215 0.5 E

237, 2215 238, 1245 0.6 E S 363, 1230 366, 0000 2.5 C C

238, 2045 239, 0545 0.4 E M

266, 2215 267, 0415 0.3 E S

293, 2200 294, 1245 0.6 E M

303, 1445 311, 1515 8.1 E, NR M

330, 1415 339, 1530 9.1 NR M

339, 1545 351, 2330 12.3 E M

351, 2345 366, 0000 14.0 NR M


13

Annual Discharge and Rainfall Plots

The following pages show annual plots of stream discharge and rainfall for the Arboleda and

Taconazo watersheds.

Stream discharge is plotted in four colors:

black line: measured (stage measured by sensor, discharge calculated using equations given

earlier for sharp-crested V-notch weirs)

blue line: estimated gap-fill discharge simulated with TOPMODEL (for gaps during which

rainfall occurred)

red line: estimated gap-fill discharge linearly interpolated between the measured values

immediately before and after the gap (for gaps during which no rainfall occurred)

green line: discharge re-calculated from stage, after a correction to the measured stage

value.

In addition to these lines representing 15-minute (black and red) or 30-minute (blue) discharge

values, the solid black dots shown on the graphs represent discharge values calculated from

weekly visual measurements of stream stage (the field technician read the stage on the staff

gauge in the weir pool and recorded the value; stream discharge was then calculated from these

visual stage observations using the same weir equations utilized for the 15-minute stage data

collected with the electronic monitoring equipment).

Rainfall (plotted as gray 30-minute bars) was obtained from OTS, with gaps filled as explained

in Zanon (2011). Rainfall data are the same between the Arboleda and Taconazo plots for a

given year.

14

Day, 2006

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

in)

0

20

40

60

80

Dis

char

ge

(m3

/min

)

0

5

10

15

20

25

30

35

40

45

50Arboleda, 2006

Day, 2006

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

in)

0

20

40

60

80

Dis

char

ge

(m3

/min

)

0

5

10

15

20

25Taconazo, 2006

15

Day, 2007

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

in)

0

20

40

60

80

Dis

char

ge

(m3

/min

)

0

5

10

15

20

25

30

35

40

45

50Arboleda, 2007

Day, 2007

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

in)

0

20

40

60

80

Dis

char

ge

(m3/m

in)

0

5

10

15

20

25Taconazo, 2007

16

Day, 2008

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

in)

0

20

40

60

80

Dis

char

ge

(m3

/min

)

0

5

10

15

20

25

30

35

40

45

50Arboleda, 2008

Day, 2008

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

in)

0

20

40

60

80

Dis

char

ge

(m3

/min

)

0

5

10

15

20

25Taconazo, 2008

17

Day, 2009

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

in)

0

20

40

60

80

Dis

char

ge

(m3

/min

)

0

5

10

15

20

25

30

35

40

45

50Arboleda, 2009

Day, 2009

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

in)

0

20

40

60

80

Dis

char

ge

(m3

/min

)

0

5

10

15

20

25Taconazo, 2009

18

Day, 2010

1 31 61 91 121 151 181 211 241 271 301 331 361

Rain

fall (mm

per 3

0 m

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50Arboleda, 2010

Day, 2010

1 31 61 91 121 151 181 211 241 271 301 331 361

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25Taconazo, 2010

la selva weirs - ots.ac.cr laselva... · one weir was built on the taconazo stream, ... taconazo...

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