RC10 - Below Llapay HEP

Site Code: RC10. GPS: S12°34676, W75°826651. Elevation: 2908m asl.

Water Quality Data

The following river and water quality data was collected from this site:

RC10 July 2019 November 2019 November 2021
Season: Austral Winter Austral Summer Austral Summer
Date: 11.07.2019 20.11.2019 15.11.21
Time: 12.00pm 10.45am 9.00am
Width (m)   17.0 13.00
Depth (Av.) (m)   0.20 1.63
CSA (Av.) (m²)   3.32 21.19
Velocity (Av.) (m/s)   0.60 1.37
Discharge (Av.) (m³/s)   2.002 29.030
Riverbed sediment Cobbles & Boulders Cobbles & Boulders Mainly boulders
Temp. (Atmospheric) (°C) 20 23 18
Temp. (Water) (°C) 11.65 13.54 12.31
Atmospheric pressure (mbar) 695 740  
Dissolved oxygen (mg/l) 5.41 4.09 6.79
Dissolved oxygen (%) 69.6 65.6 88.5
pH 5.98 8.69 8.30
Conductivity (µS/cm) 512 453 598
Total Dissolved Solids (ppm) 256 226 299
ORP (mV) 351.5 128.9 108.8
Turbidity Clear: Clear: Clear:
Alkalinity (mg/l CaCO₃) 169 (1.6N) - 129 (1.6N)
Alkalinity Field Tester (ppm/ CaCO₃) - - -

Data Analysis

Discharge at this point along the Rio Canete has increased between July to November, suggesting that the rains had already started in the headwaters of this sub-catchment. The periods we have sampled as such fall principally within the dry season. However, rains in the high sierra do begin from mid-October. The sample point lies just beneath the El Platanal HEP station (G2) and input point. This may increase discharge by up to 4 m³/s.

At nearly 2900m asl the DO readings at RC10 are low but fall within the range to be expected for both July and November data sets. Again, the increased elevation and diurnal fluctuations in temperature in narrow, sheltered sections of the valley will produce variation in maximum absolute oxygen capacity and, in consequence, percentage saturation.

The conductivity readings at this site have been highly variable, with 453-512 µS/cm are as expected.

pH readings of 8.7 in November 2019, is as expected for a clean river. The July data requires confirmation.

Site Description

Site RC10 lies in the Rio Canete valley at 2880m asl in the arid temperate zone. It is just below the El Platanal HEP (G2) and the confluence with the Rio Laraos. The valley at this point is narrow with a pronounced v-shaped profile and steep valley. River flow is year-round and fast at this point.

There is little or no agricultural cultivation along this section of the Rio Canete, which is dominated by riparian Alders, and tall thorn scrub with scattered Eucalyptus planted for timber and building materials. Above the narrow flood plain valley sides are arid, supporting a xeric vegetation with increased woody shrubs and trees lining some of the more sheltered ravines. The limited agricultural activity results from the narrow floodplain. There is some evidence that at some point in the past the hillsides were terraced and farmed as in the Laraos valley.

This site retains the typical avifauna of the lower elevations with American Kestrel, Blue and Yellow Tanager, Scrub Blackbird, Black-necked Woodpecker, Golden Grosbeak, Chiguanco Thrush, Golden-billed Saltator, House Wren and Hooded Siskin being species that now reflect more strongly the temperature zone community. The hillsides at this elevation have relictual elements of the pacific woodlands that typify vegetative associations higher up the valley.

RC10 View upstream Site RC10 - Study site location: at lower end of straight section below Llapay HEP station. (John Forrest)

Site RC10 - the study site. (John Forrest) Site RC10 - the study site. (John Forrest)

RC10 View upstream Site RC10 - View upstream. (John Forrest)

RC10 View downstream Site RC10 - View downstream. (John Forrest)