RC12 - Villa da Arma

Site Code: RC12. GPS: S12°29821, W75°814258. Elevation: 3053m asl.

Water Quality Data

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

RC12 July 2019 November 2019 November 2021 March 2022 June 2022
Season: Austral Winter Austral Summer Austral Summer Austral Summer Austral Winter
Date: 11.07.2019 20.11.2019 15.11.2021 27.3.2022 28.6.22
Time: 15.30 12.15 11.00 16.00 12.45
Width (m) 14.0 18.0 14.0   18.3
Depth (Av.) (m) 0.97 0.80 0.91   0.64
CSA (Av.) (m²) 13.56 14.35 12.74   11.66
Velocity (Av.) (m/s) 1.10 1.06 0.90   0.83
Discharge (Av.) (m³/s) 14.96 15.235 11.466   9.675
Riverbed sediment Cobbles & Boulders Cobbles & Boulders Mainly boulders   Pebbles, cobbles & boulders
Temp. (Atmospheric) (°C) 18 24.5 18 14 21
Temp. (Water) (°C) 11.48 13.13 12.95 12.77 12.00
Atmospheric pressure (mbar) 605 708   713 604
Dissolved oxygen (mg/l) 5.07 3.99 6.67 4.65 7.37
Dissolved oxygen (%) 66.0 64.1 88.6 74.9 112.4
pH   8.67 8.27 8.61 8.48
Conductivity (µS/cm) 525 457 602 327 541
Total Dissolved Solids (ppm) 263 229 301 164 271
ORP (mV) 347.1 154.6 166.7 64.6 161.7
Turbidity Clear: Clear: Clear: Slightly milky: blue/green Clear: blue/grey
Alkalinity (mg/l CaCO₃) 167 (1.6N) - 143 (1.6N) 146 (1.6N) 180 (1.6N)
Alkalinity Tester (ppm CaCO₃) - - - 133 162

Data Analysis

Discharge at this point along the Rio Cañete is in the range of 10-15cumecs, in other words, there is significant flow all year round at this site. The lower flow data recorded may therefore represent base flow at around 10cumecs. The rains from November to March should recharge the catchment, and raise discharge to a peak in March/April but equally sudden heavy rains in November could significantly increase the dischare ony single day. The data suggests that the rains had already arrived in the headwaters in November 2021 while in July 2019 significant rains earlier in the year were still reflected in the flow. The sample point lies just below the confluence with the Rio Alis which is major contributor to the discharge here.

At over 3000m asl the DO readings at RC12 are low but fall within the range to be expected. The DO levels are very similar for all sample times. Conductivity readings at this site range from 327-602 µS/cm. At the upper end, it is on the high side, but RC12 is located in the upper mid-catchment.

The pH readings of about 8.5 are as expected for a clean river and appropriate for most forms of aquatic life.

Site Description

Site RC12 lies in the Rio Cañete valley at 3032m asl in the arid temperate zone. It is just below the confluence with the Rio Alis at Tinco Alis. The valley at this point is narrow with a pronounced v-shaped profile and steep valley sides. River flow is year-round and fast at this point.

The level flood-plain lands are only cultivated to a limited extent. There is some limited pastoralism and subsistence production of maize and quinua but little else. The riverbanks and nearby fields are lined with Alders, broom (retama), tall thorn scrub and scattered Eucalyptus sp.

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 north facing slope is rather more densely covered with shrubs and trees associated with the relictual pacific woodlands found a little higher up the valley. This site retains the typical avifauna of these elevations as outlined for sites RC10 and RC11.

RC12 View upstream Site RC12 - Study site location: in front of the Villa de Arma lodge, below the bridge.

Site RC12 - the study site. (John Forrest) Site RC12 - the study site. (November 2019) (John Forrest)

RC12 View upstream Site RC12 - View upstream. (November 2019) (John Forrest)

image Site RC12 - View downstream. (November 2019) (John Forrest)