RT09B - Middle Alis (Above Puente Huancachi)

Site Code: RT9B. GPS: S12°25671, W75°715075. Elevation: 3750m asl.

Water Quality Data

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

T9b November 2019 November 2021
Season: Austral Summer Austral Summer
Date: 21.11.2019 17.11.21
Time: 16.45pm 11.15am
Width (m) 13.0 7.5
Depth (Av.) (m) 0.11 0.14
CSA (Av.) (m²) 1.40 1.03
Velocity (Av.) (m/s) 0.66 0.65
Discharge (Av.) (m³/s) 0.923 0.673
Riverbed sediment Cobbles & Boulders Mainly pebbles
Temp. (Atmospheric) (°C) 16 12
Temp. (Water) (°C) 10.73 11.11
Atmospheric pressure (mbar) 650  
Dissolved oxygen (mg/l) 3.64 5.41
Dissolved oxygen (%) 56.1 76.05
pH 8.62 8.27
Conductivity (µS/cm) 442 670
Total Dissolved Solids (ppm) 221 335
ORP (mV) 179.5 102.7
Turbidity Clear: Clear: slightly turbid
Alkalinity (mg/l CaCO₃) - 90 (1.6N)
Alkalinity Field Tester (ppm/ CaCO₃) - -

Data Analysis

Discharge at this point along the Rio Alis reflects the timing. Discharge rapidly declines in the latter part of the dry season.

At well over 3500m asl the DO readings at T9b fall within the range to be expected. It again shows the fall in DO readings as one ascends to the headwaters from T9a. The measurements for conductivity and total solids are high and may reflect local geological conditions and weathering processes. This is yet to be determined. At these levels of conductivity and total solids water quality is not poor. The impact of the Yauricocha mine is not known, but it is this section of the catchment where mining is concentrated.

Between November 2019 and November 2021 but probably during mid-2021, the channel above Punete Huancachi was deepended and the material excavated piled up along the right hand bank for approx. 50 metres above the bridge. The deposited material, consequently, also significantly narrowed the channel.

Site Description

Site T9b lies in the arid temperate zone above the small town of Tomas at 3689m asl. It is located in the temperate zone in the upper valley. At this point the valley retains a v-shaped profile. The classic U-shaped valley profile of glaciated uplands only appears in the uppermost sections of the headwaters and close to Mina Yauricocha. The bed load in the river channel is comprised of fluvio-glacial boulders, gravels, and sands. The river flow in the Rio Alis here is year-round with discharge at this time perhaps approaching base flow.

There is little or no agricultural cultivation taking place at present, with pastoralism dominating rural land use. There are extensive areas of terracing on steeper and more mesic west facing slopes. Although these slopes are largely unused nowadays, the traditional practice of burning hillsides can be clearly seen. This is a highly detrimental practice; accelerating soil erosion, reducing slope stability and reducing biodiversity. It is undertaken to promote grazing for the tiny number of goats, sheep and cattle held by subsistence farmers.

Changes in agricultural production reflecting both population declines in the early period of Hispanic colonisation and, more recently, rural drift. The riverbanks are dominated by riparian scrub and small alders with stands of Eucalypts. Above the uneven flood plain valley sides are dominated by arid scrub, with polylepis groves clinging to the sheltered watershed slopes. This site displays a fauna and flora typical of the high temperate habitats. Chiguanco Thrush, House Wren and Hooded Siskin remain. Cream-winged and White-winged Cinclodes, Striated Earthcreeper, Peruvian Sierra Finch, Plumbeous Sierra Finch, Band-tailed and Plain-coloured Seedeaters, and Black-throated Flowerpiercer are common here.

High above the settlement of Tomas there are areas of bofedales and polylepis groves which support populations of several rare and endangered species. Bofedales here are considered possible sites for the critically endangered White-bellied Cinclodes (Cinclodes palliatus). In these areas the critically endangered White-bellied Cinclodes may occur, along with Diademed Sandpiper-Plover (Phegornis mitchellii). These are both specialised species, whose presence is indicative of high environmental quality, as they are highly sensitive to water quality changes.

This valley is the principal transport route to Huancayo, with daily bus services to that city. Above the Mina Yauricocha the road widens and is also used by heavy trucks to access the mining centre of La Oroya.

Site T09B - the study site location. (John Forrest) Site T09B - the study site location just above Puente Huancachi. (John Forrest)

Site T09B - the study site. (John Forrest) Site T09B - the study site. (November 2019) (John Forrest)

Site T09B - View downstream from the study site. (John Forrest) Site T09B - View downstream from the study site. (November 2019) (John Forrest)

Site T09B - View upstream from the study site. (John Forrest) Site T09B - View upstream from the study site. (November 2019) (John Forrest)