Saja River

The Saja is a river located on the Cantabrian slope of the Iberian Peninsula, which runs entirely within the autonomous community of Cantabria (Spain). It rises on the north face of the Sierra del Cordel at one thousand eight hundred and ninety meters above sea level, within the Campoo-Cabuérniga Commonwealth, and flows into the Cantabrian Sea after traveling seventy-two kilometers, giving shape to the wide estuary of San Martín de la Arena between the municipalities of Suances and Miengo.

The upper course is protected within the Saja-Besaya Natural Park, which occupies the entire headwaters of the river and a large part of the watershed between it and its main tributary, the Besaya River. Its route forms the valleys of Cabuérniga and Cabezón de la Sal, located respectively to the south and north of the Sierra del Escudo de Cabuérniga; and the plains of Casar de Periedo, Puente San Miguel and Torrelavega that extend until they reach the sea. The basin has a total area of 1048.24 km² and is populated by more than one hundred thousand inhabitants, mainly concentrated in the municipalities of Torrelavega, Los Corrales de Buelna, Reocín, Cabezón de la Sal and Suances.

The name 'Saja' It comes from the Latin name Salia, whose origin dates back to pre-Indo-European languages before Celtic and can mean stream or salt water.

In the past, the river was used to move several dozen flour mills and fulling mills, now abandoned or missing. It currently feeds a fish farm and several waterfalls for electricity production, as well as hosting a river port very close to the town of Torrelavega and another at its mouth.

Etymology

Hydronímic Charter of the Former Indoeuropeo for the Root ♪ Sal-, ♪ Salm-.

The name Salia, by which this river was formerly known, is an inheritance that the Romance languages took from the Latin hydronym Salia or Saunium , and which has its origins in the pre-Indo-European root *Sal - "water". According to the Indo-European linguistics specialist Martín Sevilla Rodríguez, the term Salia could mean "Running Water".

This same root appears in the origin of numerous European hydronyms such as the Seille river, a tributary of the Moselle, in Gaul; the Hayle river, in Britain, or the Sella river in Asturias; all of them formerly called Salia.

Geography

The Saja river is formed in the ports of Sejos, on the northern slope of the Sierra del Cordel, when the Hitón channel joins the Guariza river in the place known as La Robrea, at thousand three hundred meters above sea level. The Guariza River, the main of the two courses, rises four kilometers above, on the slopes of Cordel Peak at an altitude of 1,899 meters.

The course of the Saja draws a great arc, first to the north and then to the northeast, until the confluence with the Besaya in the town of Torrelavega. From the junction with the Besaya, it returns to the north to cross the municipality of Polanco and die in the Cantabrian Sea after traveling a total of seventy-two kilometers. At the mouth it forms a ten kilometer long estuary that occupies an area of 3.9 km².

High Course

Rio Saja at its pass through the town of Saja in the municipality of Los Tojos, Valle de Cabuérniga.

The upper course of the Saja River begins with the source of its main sources Corva, Guariza and Diablo on the slopes of Cordel and Horcada above eighteen hundred fifty meters above sea level, and extends to the town of Fresneda at three hundred and forty meters above sea level. that the erosive character, already characteristic in itself, increases in the upper courses.

During the first kilometers its course runs rapidly through a basin boxed in a 'V', which crosses the Sejos pastures and the Cureñas channel, a narrow limestone valley with abundant rapids and waterfalls. In this first section, the currents of the Infierno channel, the Costanilla channel, the Sel de San Martín ravine and the Cambilla river come together, the latter coming from the ports of Palombera.

From the junction of the Cambilla, in the place known as the Mina Lápiz, the slope decreases slightly and the river crosses its first town, Saja. It continues its descent to the town of Fresneda, collecting along the way the waters of the Argoza river and the Valfría canal. It is noteworthy the size of the Argoza river, which joins the Saja at the height of Correpoco with a flow and length comparable to that of it.

The vegetation, sparse in the upper part, becomes very thick as the river narrows, confusing the riparian forest with the characteristic deciduous forest of the area with a clear predominance of beech forests.

Middle and low course

The Saja River in its middle course. Panoramic of the myths of Barcenillas and Ruente. Deep down the Hoz de Saint Lucia.

The middle and lower course of the river begins in the town of Fresneda and extends to the municipality of Polanco, forming the infill valleys of Cabuérniga, Cabezón de la Sal, Reocín and Torrelavega.

From Fresneda, the decrease in the slope causes the speed of the river to decrease, forming the valleys of Cabuérniga and Cabezón de la Sal. Hydrologically, they are two braided river plains connected by the Santa Lucía gorge, a small gorge formed by the river as it crosses the Sierra del Escudo. Cabezón Valley the San Ciprián stream whose source is located on the north face of the Sierra del Escudo.

After detaching from the heaviest haulage, the basin narrows slightly in the town of Virgen de la Peña, which immediately opens to form the Casar, Puente San Miguel, and Torrelavega floodplains. The most important addition in this section is that of the Besaya river, which converges in the town of Torrelavega to contribute to the formation of the valley.

Mouth

Ria de San Martín de la Arena from Requejada (Polanco) to the Cantabrian Sea.

Finally, the Saja flows into the San Martín de la Arena estuary or Suances estuary, an estuary eight and a half kilometers long from the port of Requejada to the tip of Dichoso. It occupies an area of 3.9 km² between the municipalities of Suances, Polanco and Miengo, and it is navigable for shallow draft boats throughout the central channel. The páramos subjected to the fluctuation of the tides occupy 75% of its surface, and the water flows are modified by the artificial structures that delimit the navigation channel up to the Requejada wharf. The average flow thrown into the sea by the Saja at the beginning of the estuary is 24.2 m³/s. The quality of the water in the estuary is considered to be poor, mainly due to discharges from the collectors of three chemical and paper industries and another eleven urban wastewater.

The innermost section of the estuary, almost completely fluvial in nature, begins between Viveda and Barreda and supports great industrial pressure. This pressure is attenuated in the next stretch, known as Vuelta Ostrera, where there is a wastewater treatment plant. As you move towards the sea, the vegetation intensifies until you reach the area called la Ribera, where the port of Suances and the homonymous beach of La Ribera are located. This extends to the end of the course defined by two concrete breakwaters. The mouth of the estuary is delimited by Punta del Torco and Punta de Afuera, which are in turn the northern limits of La Concha cove, in which are the beaches of La Concha and Marzán.

In the most northwestern part of the mouth, thirty-five meters above sea level, is the Punta del Torco de Afuera lighthouse or Suances lighthouse, a 9.35-meter-tall white tower built in the mid-19th century.

Hydrography

The river is seventy-two kilometers long and has an average flow at the mouth of 24.65 m³/s, of which approximately half (12.1 m³/s) corresponds to the Besaya River.

Flow rate

Its average daily flow is 12,024 m³/s in the town of Puente San Miguel and 24,224 m³/s in the town of Torrelavega, after the junction of the Besaya River. At its mouth it is estimated that the flow amounts to 26,033 m³/s.

The following tables show the average flows of the Saja River at the height of the towns of Puente San Miguel and Torrelavega during the period 1970-2000.

Media del Saja in Puente San Miguel

Means of the Saxon at your pass through Torrelavega

Regarding the interannual average, the highest quarterly average flows correspond to the second quarter (April, May and June) with figures above forty cubic meters per second, while the lowest monthly average flows are associated with the dry season, with values around seven cubic meters per second.

Hydrological regime

The hydrological regime of the Saja is strongly determined by the rainfall variations in the region. The large floods of the river usually occur from November to February and in the month of April, while the lowest flows occur between July and October, with the minimum in the month of July. All this conditions a very irregular course, with strong fluctuations in flow.

Floods and river conditioning

These spring precipitations cause relatively rapid rises in the river flow, popularly known as full, which as it passes through the valleys of the valleys usually produces numerous floods, which do not pose a risk Significant, since the main urban structures are located far from the channel, on the upper terraces, where the degree of flooding is lower and is associated with events of great magnitude and low frequency. Some of the most intense floods occurred in the years 1953, 1983, 2010 and 2019, especially affecting the valleys of Cabuérniga and Cabezón de la Sal.

In order to alleviate the negative effects of these situations, different conditioning works and projects have been carried out, both in the riverbed and in flood-prone areas aimed at both preventing the risk of flooding and preserving river ecosystems. These works have gradually changed the braided morphology of the river into more or less canalized and rectilinear sections, as can be seen in the Cabezón de la Sal plain, where the only sector that preserves a clear braided morphology is the final stretch of the river. river, near Ontoria.

Basin

Watershed of the Saja River.

The Saja is the main river of the Saja-Besaya system, the largest hydrographic basin in Cantabria, made up of the sub-basin of the Saja river, the Besaya river and the coastal area that empties into the San Martín estuary. This basin receives an annual rainfall of 1,214.3 hm³, of which 777.5 reach the sea through its main channel, which reaches a gross flow of 24.65 m³/s at the mouth. The total area of the system is 1048.24 km², of which 465.41 belong to the Besaya sub-basin and 93.56 to the coastal zone.

The western and eastern limits of the system are defined by the divides with the basins of the Nansa and Pas rivers, respectively. To the south, the boundary is marked by the dividing line with the Ebro river basin and to the north it is bordered by a group of small basins that discharge their waters directly into the Cantabrian Sea and the Cantabrian Sea itself.

Within the Saja-Besaya system are the municipalities of Santiurde de Reinosa, San Miguel de Aguayo, Pesquera, Bárcena de Pie de Concha, Los Tojos, Molledo, Anievas, Arenas de Iguña, Cabuérniga, Cieza, Ruente, Los Corrales de Buelna, San Felices de Buelna, Mazcuerras, Cabezón de la Sal, Reocín, Torrelavega, Polanco, Suances and partially, Campoo de Enmedio, Campoo de Yuso, Brotherhood of Campoo de Suso, Valdáliga, Udías, Alfoz de Lloredo, Santillana del Mar and I lie. As for populations, in the year 2014 there were six towns with more than 5,000 inhabitants: Torrelavega (26,481 inhabitants), Campuzano (10,710 inhabitants), Los Corrales de Buelna (9,261 inhabitants), Tanos (6,106 inhabitants), Cabezón de la Sal (5,250 inhabitants) and Suances (5,016 inhabitants).

Its characteristic drainage network, made up of two rivers that are very similar in terms of length and flow, give this basin an atypical character within the region.

The upper third of the basin is highly erodible, especially at the headwaters of the Saja, composed of clays and sandstones from the Lower Cretaceous, which are softer than the Jurassic limestones present at the headwaters of the Besaya. The middle and lower zone is occupied by wide valleys of landfills such as Cabuérniga, Cabezón de la Sal, Iguña, Corrales de Buelna, and Torrelavega. The relief of the basin is strongly rugged with an average slope of 29.17% and an average altitude of 610 m with maximum altitudes that exceed two thousand meters at the head of the Saja. Regarding the permeability of the rocky substrate, low permeability terrains predominate, which represent 58% of the total surface, while those with high permeability occupy approximately 36%. The average values are not relevant, less than 6% of the total area.

Main tributaries

The tributaries of the Saja, as with most of the rivers in Cantabria, have a fairly short route due to the orography of the region and are affected by a strong dry season, which even dries up some channels during the summer months. Most of the tributaries of the Saja flow into it on its right bank.

Conservation status

The ecological conservation of the river is very good from the headwaters to the town of Cabezón de la Sal, point from which it already presents slight alterations and its state of conservation is only defined as «good». Downstream from the confluence with the Besaya river, the alterations are already serious or very serious, classifying the section as "poorly preserved". This is due to the fact that the basin is home to a highly industrialized area in which legal discharges must be added numerous illegal discharges that have been carried out historically.

Pressures and impacts on the Saja River

Although the alterations in the river are not very numerous (3.1 per km), some of them have a significant magnitude, especially those that are concentrated in the middle and lower reaches of the river.

The Saja river is one of the rivers with the most channels recorded in all of Cantabria, in addition to having eleven catchments and twenty dams, which together with the numerous bridges (thirty-one) significantly alter the water regime, the continuity of the system and the hydromorphological conditions of the channel.

The numerous and important discharges of industrial and urban wastewater are the main responsible for the generalized deterioration of water quality, especially from Puente San Miguel and Torrelavega. It should be noted that, in addition to receiving untreated wastewater from the second largest population center in Cantabria, various polluting industries (Textil Santanderina, Azsa, Firestone, Sniace) are found on the banks of the river, most of which are included in the EPER registry.

Finally, in the lower basin there are extensive populations of feather duster and Japanese polygon, invasive plants that represent a threat to the native species of the riverbank, due to their high propagation capacity and difficult eradication.

Despite this situation, the upper section of the river up to Renedo de Cabuérniga is little altered and has a high environmental interest, with large areas in a very good state of conservation.

Protection spaces

Paleartic nutrition.

Iberian demise.

White-footed river crab.

• ZEC Rio Saja

It is located in the middle and upper reaches of the Saja, between the border of the Commonwealth of Campoo-Cabuérniga (near kilometer fourteen of CA-280) and the Santa Lucía bridge. This figure protects a total of 321.28 hectares within the space previously delimited, including the channels of the Saja river and a large part of the Argoza, Viaña, Monte Aa and Bayones rivers, in addition to a fixed band of twenty-five linear meters to both sides of all channels.

The most common habitats are aluba alisa (Alnus glutinosa) and ash (Fraxinus excelsior) forests, followed by acidophilus beech forests, dry heaths and oak woods Galician-Portuguese. Among the most representative animal species we find the crayfish (Austropotamobius pallipes), the Iberian desman (Galemys pyrenaicus) or the Palearctic otter (Lutra lutra)), whose population in the middle and upper reaches of the river is one of the best in Cantabria.

In 2006, the Saja River was included in the network of natural spaces of Cantabria as a place of community importance.

• ZEPA Sierra del Cordel and Nansa and Saja headers

The headwaters of the Saja, together with the headwaters of the Nansa, are included in the Special Protection Areas for birds (ZEPAS) as well as being part of the Brown Bear Recovery Plan in Cantabria.

• Saja-Besaya Natural Park

A large part of the upper basin is integrated into this park, declared a natural park in 1988 and which occupies 24,500 ha. between the basins of the Saja and Besaya rivers.

The protected area has a great wealth of fauna and flora with wooded areas of great interest, especially in the basin of the Bayones river, the Argoza and the Saja as it passes through the Cureñas channel. Among the numerous species, the wild boar, woodcock, otter, wolf, golden eagle and roe deer stand out. The deer, reintroduced in 1949, is currently found throughout the territory; their bellowing during the mating season is a claim for thousands of visitors. In the southern part of the park it is possible to observe the Cantabrian brown bear.

The natural park overlaps with the following figures of the Natura2000 Network:

• LIC Valles Altos del Nansa y Saja y Alto Campoo.
• LIC Rio Saja.
• ZEPA Sierra del Cordel and Cabeceras del Nansa y del Saja.

• Saja regional hunting reserve

The upper basin of the Saja river and part of the middle basin are located within this reserve, which with 180,186 hectares is the largest in Spain, extending from the Picos de Europa to the eastern limit of the Besaya river. This reserve hunting was created in 1966 and maintains a high degree of conservation. Within it is the Saja-Besaya natural park, the Río Saja SCI and the ZEPA Sierra del Cordel and Cabeceras del Nansa and Saja.

• LIC High valleys of Nansa and Saja and Alto Campoo

This extensive Site (51,098 ha) encompasses the Saja-Besaya Natural Park and the Peña Labra, Cordel and Peña Sagra mountain ranges.

It is an area of medium and high mountains made up of a rich mosaic of grasslands, forests and bushes modeled by traditional extensive cattle exploitation that significantly increases the biodiversity of the area. Among the fauna, the presence in Alto Campoo of the brown bear stands out, which has in Alto Campoo the eastern limit of its recovery area. It is also worth noting the presence of twenty-five taxa of the directive, two of them priority.

• Natural river reserve Head of Saja

Due to the good ecological condition of the upper section of the Saja river, a total of 9.78 km formed a fluvial natural reserve declared in 2015. It is a representative section of the Cantabrian humid calcareous mountain rivers.

Fauna and flora

Common salamander.

Common trout.

The numerous protection spaces that the Saja River crosses are a sample of the important ecological value, both in terms of fauna and flora, of this basin.

Wildlife

In the fluvial environment of the Saja River, more than thirty different species of vertebrate fauna have been detected, including fish, amphibians, reptiles, birds and mammals.

Fish such as eels, minnows, brown trout, and rainbow trout are common in the riverbed, as are amphibians such as salamanders, alpine, webbed, and marbled newts, common and midwife toads, and common and common frogs, and some crustaceans such as the signal crab or the American river crayfish.

You can also find reptiles such as the collared snake or the viperine snake and small mammals such as the otter, the riverside bat, the marten, the shrew, the polecat, the marten or the Iberian desman.

As for the bird life, the kingfisher, the sand martin, the sandpiper and the white wagtail, the dipper, the cormorant, the gray heron and the egret, the mallard, the European quack, the common redfish and the Common sandpipers are the most common species.

Moving away from the river bank at the headwaters of the Saja, the fauna is typical of the Cantabrian mountain range, with abundant deer, roe deer and wild boar. Also noteworthy are wolves and chamois on the peaks near the source of the river, as well as numerous small mammals.

The case of the brown bear, in danger of extinction, whose presence is sporadic but regular in the southwestern sector, and other protected species found in the basin, such as the gray dormouse, the polecat, and the wildcat.

In this area there are around a hundred nesting species, among which are the golden eagle, the short-toed eagle, the kite, the common buzzard or the griffon vulture.

Flora

Instant of a nest in the Saja-Besaya Natural Park.

Vegetation varies along the course of the river, where the milder conditions of the coast contrast with those of the high valleys and peaks.

In the high parts, above 1,200 meters above sea level, the presence of trees is very scarce, almost non-existent above 1,400 meters, being limited exclusively to birch, holly and rowan; however, the scrub areas are very abundant (around 43% of the surface), especially the different species of heather and broom. This high mountain landscape alternates with areas of communal grasslands, rocks and garmas.

Beech is predominant in the range between 600 and 1,200 meters above sea level, where it forms extensive forests such as Monte de Saja, which with an extension of more than 6,500 hectares represents the largest beech forest in Europe. The oak prefers altitudes between three hundred and seven hundred meters, where three main species can be found: the cajiga (Quercus robur), the sessile oak (Quercus petraea) and the rebollo or Tocio (Quercus pyrenaica). The best oak groves are in the municipality of Ruente, in the mountains of Ucieda and Monte Aa. The latter is considered one of the best oak groves in Cantabria, thanks to the local climate it enjoys as it is to the south of the Sierra del Escudo.

Accompanying these main species are others such as birch, whitebeam, elm, rowan, hazelnut, blackthorn, holly, ash or willow. In the Bárcena Mayor mountain there are some isolated yew trees. The replacement scrub of the forests described is made up mainly of brooms and heather in the upper parts and brambles and gorse in the middle and lower parts. The ferns are well represented with two different species: Pteridium aquilina in the sunny areas and Polistichum fillixmas in the shady and humid valleys.

Almost all of the flat areas and the hills and peaks are occupied by grasslands, of great importance for extensive livestock farming and species of hunting interest.

In the Cabuérniga valley, the banks of the river are characterized by riparian forests of alder, willow and hazelnut trees, occasionally accompanied by poplar plantations.

From the Hoz de Santa Lucía the vegetation changes considerably. Samples of native trees disappear almost completely to be replaced by eucalyptus and pine plantations. Similarly, the dominance of communal pastures and meadows over land and urban terrain is reversed.

Hydraulic use

The hydraulic use of the river was intense in antiquity with a multitude of fulling mills and flour mills. Proof of this is that in the Cabuérniga valley alone, twenty-four mills and two fulling mills were recorded in the 18th century. Currently, it is reduced to industrial use, with two dams in the course of the river.

The most important is the so-called Sniace dam, which is located immediately upstream of the confluence with the Besaya River.

If you continue upstream, you will see the Santa Lucía dam, which is located in the gorge of the same name that closes the Cabuérniga Valley. It is a dam built at the point where it joins the Saja with the Bayones river. The purpose of this dam is the production of electrical energy and it is operated by the company Textil Santanderina.

Port of Requejada

Requejada port (lower part of the image) seen from a commercial plane.

In the lower part of the river course is the river port of Requejada, located about 4 miles from the mouth, owned by Julio Cabrero & Cia S.A.. The port has not operated since the year 2008, when the Cantabria Maritime Captaincy stopped sealing dispatches, considering this port unsafe, due to the accumulation of sand and stones on the bottom. These problems with little sounding have caused that since 1874 thirty-seven medium-draft vessels have run aground (one every eighteen months). The last grounding was that of the mini-bulk carrier Explorer. This bulkcarrier of 1,600 tons and a maximum draft of 4.2 m was trapped by the sand on March 14, 2007, at the exit of the Cuchía breakwater, when it was loaded with 1,900 tons. of sodium bicarbonate from the Solvay company. The ship could not be released until four days later.

Before being the main port for companies such as the aforementioned Solvay chemical company, the Asturiana de Zinco mining company and the Sniace wood pulp extraction company, Requejada was the main point of departure for Castilian flour during the 19th century XIX, until the Alar-Santander railway line was opened in 1852.

Although it experienced growth in the movement of merchandise in the early nineties, it declined to forty-one million tons in two thousand and six. The port has been closed since 2008, despite the attempt to reopen it by the mayor of Polanco and the owner of the company that manages the port, appealing to its utility due to its proximity to companies in the Besaya basin. In 2011, it was estimated that an investment of €50,000,000 would be necessary, and an increase of twenty-four times the volume of activity of 2007, which makes reopening unfeasible in the short and medium term.

Fishing tradition

The Saja River is a river with a fishing tradition that currently has three trout reserves and a sports fishing arena in its main channel.

The largest of them is the Coto Caranceja with eight thousand two hundred meters in length and whose limits extend from the Golbardo bridge to the confluence of the Rey river with the Saja. Next is the Cabuérniga that covers the course between the Viaña bridge and the junction of the Argoza river, and that connects its 5,215-meter preserve with the 9,047 m of the Barcena Mayor preserve. which comprises a large part of the route of the Argoza. Already in the upper course of the river is the pozo el Amo reserve extending from the town of Saja to the bridge over the well itself (3700 m). Lastly, the Rudagüera sports arena is an area delimited at its ends by the San Pedro de Rudagüera railway station and the Golbardo bridge. This sporting venue, next to the Caranceja preserve, has been home to the Río Saja Fly Fishing Masters organized by the Puente San Miguel Fly Fishing Club since 2010..

Aquaculture

In the municipality of Ruente is the Truchas del Saja fish farm, dedicated to raising and fattening rainbow trout (Oncorhynchus mykiss). The fish farm has an estimated annual production of 211,000 kilograms and an area of 1,225 hectares, within which there are several ponds of different sizes.

The ponds are supplied with water from two intakes located on the Saja river and the La Fuentona de Ruente stream, which in total provide a flow of six hundred liters per second of water.

History

Reproduction of the roof of the Altamira polychrome room at the Deutsches Museum in Munich.

Prehistory

The first traces of human occupation in the Saja Basin date back 35,600 years, during the Aurignacian period. These are located in the lower area of the basin, in the municipalities of Reocín, Torrelavega and Santillana del Mar, highlighting among all of them the Altamira cave, which preserves one of the most important pictorial and artistic cycles of Prehistory worldwide, cataloged as a World Heritage Site in 1985. In the municipality of Reocín, the caves of La Clotilde and La Estación, although of lesser importance, also house cave paintings, which is why they were declared an Asset of Cultural Interest in 1997.

Anthropomorphic lax with engravings on the Sejos hill.

For its part, at the headwaters of the river, the first traces of human activity are those found in the Megalithic Station of Collado de Sejos-Cuquillo, dating from the end of the Copper Age or the beginning of the Bronze Age. It is a set of menhirs, burial mounds and circular structures located in the watershed between the Saja and the Nansa, studied for the first time in 1850 by Ángel de los Ríos. After the latest studies by Primitiva Bueno and other researchers, this megalithic complex can be considered the most important in Cantabria. It has recently been declared a site of cultural interest.

Old Age

According to the writings of Strabo, Pliny the Elder and Pomponio Mela, at the end of the 1st millennium BC. C. the basin of the Saja was in the territory inhabited by the ancient Cantabrians. It is probable that the upper part was occupied by the Salaenos tribe, while the lower areas and the Besaya sub-basin were occupied by the Blendios.

The later Roman presence left little trace in the region, being limited to a series of secondary roads such as the one that linked Pisoraca (Herrera de Pisuerga), with Portus Blendium (Suances), probably crossing the Besaya valley or with the Portus Vereasueca (San Vicente de la Barquera) through the Somahoz pass. An Agrippa road, meanwhile, crossed the current municipality of Polanco connecting Portus Amanum (Castro Urdiales) with Portus Vereasueca.

With the fall of the Roman Empire, a little assimilated Romanization came to an end, which receded as the old customs and social organization were recovered. During this period, there are no written references to the area and architecturally only one Visigothic fountain remains in the town of Colsa.

Middle Ages

The extension of agriculture, together with the incipient spread of Christianity and the population increase, especially from the 8th century, were the main triggers for sedentarization and the origin of the first villages, as is the case of Santillana del Mar.

In the IX century, the upper valley of the Saja once again gained relevance as one of the ways of repopulating the plateau after the population vacuum caused by the wars between the Emirate of Córdoba and the Kingdom of Asturias. This route was popularized in 1956 by Víctor de la Serna under the name of Ruta de los Foramontanos. The first population centers of Cabuérniga, then called Kaorneka, arose at this time: La Miña, Bárcena Mayor... The towns of Ruente, Polanco and La Vega (present-day Torrelavega) probably formed a few centuries more late.

Since the XII century, there is knowledge of the importance of the port of San Martín de la Arena, which supported a high volume of whaling and trade.

Modern Age

From the 17th century, due to the silting up of the estuary, the port activity of San Martín de la Sand begins to descend, while the port of Requejada gains importance as a place for the export of wheat from Castilla.

Heritage

Bridge of Golbardo

Golbardo Bridge

The Golbardo Bridge is a concrete bridge that rises over the Saja River connecting the towns of Barcenaciones and Golbardo, in the municipality of Reocín.

It was built by the engineer José Eugenio Ribera in 1902, becoming one of the first reinforced concrete bridges built in Spain. On April 19, 2002, it was declared an Asset of Cultural Interest, with the category of monument due to the originality of the construction in terms of its typology, material used and construction system, which consists of using metal joists on which to suspend the metal formwork.

Punta del Torco de Afuera Lighthouse

Suances Lighthouse

In the most northwestern part of the mouth is the Punta del Torco de Afuera lighthouse or Suances lighthouse. It is a truncated white tower with the focal plane 9.35 meters above the ground, and thirty-five meters above sea level. Next to the tower is a rectangular house with a single floor, the former residence of the lighthouse keeper. The lighthouse came into operation in 1863 with a lighting system based on an oil lamp. It currently works with electric lighting, emitting flashes every twenty-four seconds, visible from twenty-two nautical miles.

Climate

The Saja basin is located in the Iberia Verde climatic region with a Western European climate, also classified as a humid temperate climate with cool summer of the Cfb type according to the Köppen climate classification.

The main features of the basin at a general level are mild winters and cool summers, without sudden seasonal changes, with the difference between winter and summer being about ten or twelve degrees. The air is humid with abundant cloudiness and rainfall is frequent in all seasons of the year, reaching an annual average of around 1,200 mm.