Puquios

Puquios (from Quechua pukyu meaning source, spring, or water well) are ancient systems of subterranean aqueducts which allow water to be transported over long distances in hot dry climates without loss of much of the water to evaporation. Puquios are found in the coastal deserts of southern Peru, especially in the Nazca region, and northern Chile. Forty-three puquios in the Nazca region were still in use in the early 21st century and relied upon to bring fresh water for irrigation and domestic use into desert settlements. The origin and dating of the Nazca puquios is disputed, although some archaeologists have estimated that their construction began about 500 CE by indigenous people of the Nazca culture.

The technology of the puquios is similar to that of the Qanats of Iran and other desert areas of Asia and Europe, including Spain. A few puquios in northern Chile and in other parts of Peru were probably constructed at the initiative of the Spanish after the conquest of the Inca Empire in the 16th century.

Chile
The puquios first became a subject of study in the early 20th century. Although they had been known before, historic evidence was scarce. Around 1900 scholars noted that puquios, locally known as socavones (lit. shafts), were spread through the oases of Atacama Desert. In the 21st century, puquios, in various states of use and decay, still exist in the valleys of Azapa and Sibaya and the oases of La Calera, Pica-Matilla and Puquio de Núñez. In 1918 geologist Juan Brüggen mentioned the existence of 23 socavones (shafts) in the Pica oasis, yet these have since been abandoned due to economic and social changes. The puquios of Pica-Matilla and Puquio Núñez tap the Pica Aquifer.

Nazca puquios in Peru
The puquios of the Nazca (or Nasca) region are of most interest to archaeologists as the area was the center of pre-Columbian civilizations such as Nazca culture which flourished from 100 BCE to 800 CE. Most archaeologists believe that the Nazca puquios are of pre-Columbian origin, but some believe that they were built by the indigenous subjects of the Spanish colonists in the 16th century. The theory of a Spanish origin holds that the puquios technology is not substantially different from Spanish techniques used from the early conquest to drain mines. An early example is the mine of Potosí that was drained by subterranean canals as early as 1556 following instructions of Florentine engineer Nicolás de Benito. Another argument for the Hispanic origin of puquios is that a Spanish law in Peru decreed that water from pre-Hispanic waterworks must be shared among landowners while the water from Hispanic waterworks could be owned by a single landowner. In an 18th-century legal case, a judge ruled in favor of the Hispanic origin of the puquios in the Chancay valley.

Proponents for the pre-Hispanic origin of the Nazca puquios cite the establishment of large settlements in river valleys with puquios in the 6th century CE, an indication that the settlement was stimulated by the water supplied by the puquios. They interpret Nazca culture iconography as portraying puquios symbolically. Climatic change may also have been a factor as the region entered several centuries of extreme aridity after about 400 CE which required the construction of irrigation works, presumably puquios, to provide water for domestic use and irrigation. The first known historical writing to refer to puquios in Nazca was in 1605 by the Spanish cleric Reginaldo de Lizárraga. Lizárraga mentions that the "indios" (indigenous peoples) of the region made use of the puquios but does not specifically attribute their construction to either the Spanish or the indigenous people. He also mentioned the much-diminished population of the indigenous people, their numbers a fraction of their pre-Columbian population due mostly to epidemics of European diseases.

In the early 21st century Rosa Lasaponara, Nicola Masini, and their team of the Italian CNR (National Research Council), in cooperation with archaeologist Giuseppe Orefici, studied the Nazca puquios using satellite imaging. They found evidence that the puquios system was once much more extensive. Scholars were able to see how the "puquios were distributed across the Nazca region, and where they ran in relation to nearby settlements – which are easier to date." Satellite imagery also revealed additional, previously unknown puquios in the Nazca drainage basin. The team that conducted this study concluded that the puquios are pre-Hispanic. In addition, RPAS (Remotely Piloted Aircraft Systems), or drones, were used in 2016 to map and document five sample aqueduct systems in the Nazca region.

A scientific method to precisely date the puquios has not been found, but, despite doubts, the "general consensus in 2017 was that the Nazca puquios were of "pre-Hispanic, Middle Nasca [c. 500 CE] origin...with subsequent Spanish and Republican modifications." The pre-Columbian origin of the Nazca puquios does not contradict the likelihood that the origin of other puquios scattered sparsely around the Central and Southern Andes is Spanish.

The technology of the puquios is similar to that of the qanats of Iran and Makhmur, Iraq, and other ancient filtration galleries known in numerous societies in the Old World and China, which appear to have been developed independently. They are a sophisticated way to provide water from underground aquifers in arid regions.

Description of Nazca puquios
The coasts of Peru and Chile are exceptionally arid with agriculture only possible with irrigation. Precipitation is less than 25 mm annually near the coast and increases only slowly at higher elevations in the inland Andes. Moreover, the Rio Grande de Nazca and its tributaries provide only sparse, seasonal water to the valleys on the Nazca region. In the past, precipitation was higher in some eras, possibly reaching an average of 200 mm annually. The people of the Nazca culture may have built the puquios to adapt to a climatic transition from greater to lesser precipitation after 400 CE and enduring until about 1100 CE, followed by a wetter period which lasted until about 1450 CE at which time another drier era began that persisted into the 21st century. The Nazca culture flourished in the area from 200 BCE to 650 CE.

The Nazca puquios are found along five of the nine named feeder streams into the Rio Grande de Nazca. From south to north, the rivers with puquios are Las Trancas, Taruga, and the Nazca, which has two tributaries, the Tierras Blancas and the Aja. The sources of the rivers is in the Andes about 70 km from the puquios. The puquios are equally distant from the Pacific Ocean at elevations of about 500 m. These small rivers are mostly dry except during the rainy season in the Andes from January to April, but have both underground and surface sections during the dry season. The inhabitants of the river valleys constructed the puquios as sources of water during the dry season.

As of the year 2000, 43 puquios were still functioning of which 29 were near the city of Nazca in the valley of the Nazca river and its tributaries. The best known of the puquios are the Cantalloc Aqueducts. The largest pre-Columbian ruin of a settlement in the Nazca valley is Cahuachi, about 18 km downstream from Nazca and near the famous Nazca Lines. Cahuachi is located along a course of the river in which it runs on the surface and thus the settlement did not depend upon puquios as did the settlements a few kilometers upstream. Many more puquios were likely built in pre-historic times in several other river valleys of the Rio Grande de Nazca system. Deep wells have replaced the abandoned puquios.

Two types of puquios are in the Nazca region. The first is the trench puquios which is a deep, narrow ditch, usually less than one meter in width and lined with rocks, which is open to the air. The second type is the gallery or subterranean puquios which is tunneled beneath the earth to tap the water from an aquifer. The water-bearing aquifer is typically about 10 m underground, although it can be much closer to the surface. From the aquifer, the water flows through an underground tunnel downslope, emerging at the surface into a trench puquios for distribution to irrigation canals and for drinking and domestic purposes. The underground tunnel is typically about one meter square, although some of the tunnels reinforced with wood beams or in modern times with cement, can be 2 m in height. Spaced along the route of the gallery puquios are vertical shafts, "eyes" or "ojos" in Spanish, which extend from the surface to the subterranean tunnel. The "ojos" permit access to the tunnel for maintenance and repair. The funnel-shaped ojos are spaced from 10 m to 30 m apart. The length of the gallery (underground section) of the puquios ranges from a few meters to 372 m. The associated trench puquios may be as long as a kilometer.

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RPAS research
A sample of five aqueducts were studied with the use of drones in order to encompass a range of types and conditions: Cantalloc (next to the town of Nasca) – the most well-known tourist site with a still functional aqueduct system; Orcona, a nearly unknown site further from the town of Nazca), Santa Maria and San Carlos – two sites unknown to tourists, but with functioning aqueduct systems still used for field irrigation, and Gobernadora. There the section with access holes had been destroyed and "only the trench at the end of the system and the basin (cocha) remained."

The aqueducts included both those in good and bad condition; some had open trenches, and some systems retained their original circular or rectangular-shaped access holes. Aqueducts that are not being used have fallen into disrepair, and researchers believe they will soon disappear if not restored.

Data and methods

All the existing aqueducts were measured with Garmin GPS to create the basic map (Figure 3). The GCPs for RPAS were signalised by simple crosses from stones and by natural formations, and after this measured with DGPS.

After measurement, thematic maps of selected areas were created based on these observations. Five aqueducts were documented in detail by RPAS. During the 2016 expedition, only the RPAS eBee from the Swiss company SenseFly was used (Figures 4 and 5). This fixed-wing RPAS system of an ultra-light construction included changeable camera sensors. In 2016, Czech Technical University in Prague used for this project only cameras acquiring images in the near infrared band (Canon ELPH 110 HS-NIR) and in the visible range (RGB, Canon IXUS 127 HS).

The NIR camera was used for the potential detection of unknown or defunct objects, using vegetation indices or crop marks based on high reflectivity of healthy vegetation in NIR. This camera takes images in false colour (green, red and near-infrared channel), in which healthy vegetation is in red (Figure 5). Other types of RPAS such as multicopters, may be more suitable for mapping of small areas.

The group used only fixed-wing RPAS for this project in Peru. Fixed-wing EBee flights are absolutely autonomous, and it is not as noisy as multicopters (which could attract unwanted attention). It was also preferred for larger areas, as the team wanted data on more than aqueducts.

Results and discussion

For the data processing, well known software was used: Agisoft Photoscan and Pix4D. Both software’s work fully automatically, use the bundle adjustment and the image correlation technology for image data processing. Aerial images acquired during a number of flights were used for the orthophoto (GSD -geometrical resolution up to 4 cm, Figure 6), the Digital Surface Model (DSM) and the difference Digital Surface Model (dDSM) production (Figure 7). The dDSM can be created by the following workflow (processing was done in ArcGIS software): the original DSM is smoothed using digital filter (for example, applying a flowing 3 × 3 or bigger image mask, where for the central mask pixel a new value is inserted as an arithmetic average of the entire mask) and the smoothed model is subtracted from the original one. The resulting new model highlights small terrain variations, which are normally not visible or hardly to detect. This approach is often used in archaeology for the visualisation of small terrain structures or features.

For all five aqueducts, the DSM were processed, such as the orthophoto. All image results were geocoded by using on-board GNSS and IMU primarily, and during the processing by precisely measured ground control points (GCPs) measured with a D-GNSS system Leica, with some decimetres accuracy after post-processing. However, during photogrammetric image processing using bundle adjustment, it was found that some GCPs have gross errors in meters (they could not be used). These problems have already occurred during field measurements, some measurements had to be repeated, and the reason for the errors were not found (may be, the probable reason was an influence by the radio link of the nearby airport). Fortunately, an excess of GCP points were measured. The final accuracy of the transformation of the results into the reference frame was estimated in decimetres.

The aqueducts are similar in construction and use, but each is a little different – especially the access holes. Some access holes are spiral-shaped (Cantalloc), other rectangular with steps (Orcona, San Carlos), and some are wells, later reinforced with wooden beams (Santa Maria). All these aqueducts are similar in dimensions (length), but not identical. The Cantalloc aqueduct has a total of 20 access holes (19 spiral access holes), of which 15 rotate to the left and 4 rotate to the right. Unity or similarity with the spirals on Nazca Plain has not been proven.

Table 1. For information: depth of water in the access hole (numbering from the first in landscape, from the beginning)

Table 1. For information: depth of water in the access hole (numbering from the first in landscape, from the beginning). CSVDisplay Table

The DSM created by RPAS is interesting, but individual access holes don’t have the necessary detail. For this reason, all access holes were photographed by hand (manually) from the surface. 3D models (DSM) of the aqueducts based on RPAS images were complemented by ground-based images to get a more detailed model of a well-preserved aqueduct (Figure 8). More than 15 aqueducts were documented in detail from the ground, while only five of the above-mentioned aqueducts were photographed from RPAS. In this case, both image sets (from RPAS and ground-based) were processed using Pix4D and Agisoft Photoscan software. The datasets were processed separately. A common processing of both datasets was not possible due to high differences in image scales and image orientations (of both RPAS and ground-based image sets). Point clouds were generated from the datasets of oriented images; when using RPAS, with terrestrial photos, in this case a point cloud represents always one access hole. The point cloud sampling distance was approximately 70 mm in RPAS-based point cloud and 15 mm in ground-based point cloud. The detailed point cloud of each access hole documented from the ground contained anywhere from 4 to 10 million of points.

Figure 8. Aqueduct near the town of Nasca (Cantalloc); image from RPAS. Display full size

After creating basic separately processed models (point clouds, Figure 9) all models were joined to one model (one-point cloud). Geomagic Studio was used for the registration of RPAS and ground-based point clouds. The standard workflow for point cloud merging in Geomagic Studio is based on manual identification of identical points in both point clouds for the preliminary transformation and later application of the ICP (Iterative Closest Point) method for transformation adjustment. This workflow failed in this case due to the high difference in the level of detail in both datasets. The correct scale of the ground-based model/point cloud was set by using a measured distance acquired from an RPAS-based point cloud (the scale of the RPAS-based model was set by using GCPs – ground control points observed by GNSS with a final absolute accuracy in decimetres). Once both models had the same scale, the transformation of the ground-based model to the coordinate system of the RPAS-based model was accomplished. The transformation was done manually, then an expert observed the models from different views and continuously changed the transformation parameters, until the models did not fit to each other in all views (Figures 10, 11).

But that does not affect the results. With the result there is an important detail of the model, that has been significantly improved by merging with ground measurements of the individual access holes (GSD of which reached 15 mm and the overall accuracy of each access hole is in the order of cm). When we realize that these are bulk boulders, it is certainly sufficient. The model has a documentation character and can be used to visualize and realize subsequent experiments. The resulting model (RPAS and ground-based together) offers a complex view on the entire situation of the documented site as well as detailed description of the most interesting parts – access holes. Conclusion

Overall, 10 flights were performed and five aqueduct systems were documented in detail using RPAS within a resolution (GSD) of 4–5 cm during the expedition in 2016. 3D models of the documented sites were created based on a combination of RPAS and ground-based images.

The major aim of this project was the documentation of valuable technical monuments, and the creation of precise maps and 3D models, which can help scholars to understand the reasons and the technology of its construction. The transformation of ground- and RPAS-based data into one coordinate system was challenging. Some aqueducts were restored, some were, even after many centuries, still in use in agriculture, and some totally destroyed aqueducts were found as well. Despite the research of recent decades, it is not clear exactly how these water management systems were constructed and managed. -->

History
Fifty-seven small rivers along the 1500 km long desert coastline of Peru empty into the Pacific Ocean. The river valleys were cultivated by their pre-Columbian inhabitants by using irrigation, but most of the valleys had more dependable and greater surface water availability than the often-dry rivers of the Nazca region. Conversely, the agricultural society of the Nazca people flourished best where surface water was most scarce. The puquios were the technology that permitted a substantial population to exist in an intensely arid region.

The Spanish first exerted control and settled in the Nazca region in the late 16th century. Under Spanish rule the area was noted for viticulture and the production of pisco, a brandy. In 1853, the English traveler Clements Markham described the Nazca valley as "the most fertile and beautiful spot on the coast of Peru." He described the puquios and said that "the fertility is due to the skill and industry of the ancient inhabitants. Under their care an arid wilderness was converted into a smiling paradise."

In the 21st century many of the puquios are still in use but their use is threatened by industrial agriculture and production of exportable crops such as asparagus. Deep wells have replaced some of the puquios as a source of water and the number of local people with the expertise to maintain the puquios has diminished. The modest amounts of water supplied by the puquios is replenished every year by precipitation at the source of the rivers in the Andes, but the exploitation by deep wells of underground water sources for agriculture and a growing population may not be sustainable.