HIDROLOGY

THE WATER CYCLE






























The hydric resources, potential for a sustainable human development in the Department of Cauca
Mayo 01,03
Author: Apolinar Figueroa and Leonidas Zambrano translator: Helvia Braendly

In the Department of Cauca several Hydric sources are found. These contribute to the human and environmental development. The hydric resources are rivers, laggons located in the high mountain ranges, man made reservoirs and the Pacific Ocean. The Cauca river is the most important one for the Department because it, together with its tributaries contributes to human, animal and vegetal sustainability.

Hydric resources are basic for a sustainable human development in the Department of Cauca. The availability of superficial hydric resources is a contribution of vital importance for the social and environmental development of Cauca. The Department has one of the most important reservoirs of the country, one of them is Salvajina (located in the municipality of Buenos Aires). It occupies 2.200 hectares and has a total capacity of 908x106m3 of water from which 756x 106m3 are useful. The Department of Cauca also has 78 lagoons (Picture 1) with a water volume of 1065x103m3. Between marshes and swamps the water source is of 650x103m3, for a total contribution of 9581x103m3 (Marín 1992:412). Thirty of the lagoons of Cauca have a surface measure that ranges from 1.5 to 3.5 hectares, 38 whose surface is smaller than 1,5 hectares. The most important ones are El Buey (64 ha.), San Rafael (Picture 2)(26.5 ha.), Cutanga (24.7 ha.), San Patricio (20.2 ha.), Santiago (12.2 ha.), La Magdalena (7.2 ha.), Cuasiyaco (6.2 ha.) (Picture 3) and Rionegro (3.5 ha.). The territory of the Department of Cauca has important superficial water streams such as the Naya, Micay, Bubuey and Guapi rivers toward the Pacific Ocean, as well as those that originate in the Macizo Colombiano, among those stand out the Magdalena, Cauca, Patía. and Caquetá rivers. The transcendence of these basins surpasses the geographical limits of Cauca and they extend their influence so much national as internationally. In fact, basins like that of the Caquetá river has influence as far as the frontier with Brazil; Magdalena's basin that includes that of Cauca, is not only of national transcendence in the contribution of hydric resource, but in the agricultural and industrial development of the country. Because of this, the environmental and social analysis of these basins are decisive for the sustainable human development of the department.

Upper Basin of the Cauca river

The Upper Cauca river basin includes the territory located from the river spring and goes as far as the limits of the Department of Cauca with the Department of Valle del Cauca, it covers an area of 717.608 hectares, equivalent to a 23.7% of the total area of the Cauca river. The basin frames partially or totally 21 of the 40 municipalities of the Department, which has the biggest population concentration, 679.423 inhabitants that represent a 62.3% of the total population, 48.5% of which settle in urban areas (CRC 1996a:102).

The micro-basins integrating the upper region of the Cauca river are the Rio Hondo, Rio Sucio, Palacé, Seguenguito, Piendamó, Ovejas, Inguitó, Dinde, Timba, Teta, Quinamayó, Japio, Palo and Desbaratado rivers. This hydric resource generates an average annual flow of 266 m3/s, that represent 33 L/km2. Of these micro-basins that of the Palacé river has momentous importance because of its hydric contribution for the city of Popayán. Its contribution to the Cauca river is calculated in 6.5m3/s. Another basin of hydrological importance that contributes to the Cauca river is the Ovejas river because of its possible deviation to the reservoir of the Salvajina which waters an area of 105.756 hectares and that includes the Ovejas (49.765 hectares), Mondomo (25.416 hectares) and Pescador (19.525 hectares). Rivers. From their spring in the municipality of Silvia until their outlet into the Cauca river, the Ovejas river has a longitude of 71,5 kilometers and an average hydric contribution in flow of 24.3m3 of water.

The silts haulage in the basin of the Cauca is calculated in 8.2 kton/day, which means 1 daily/ton/km2 (CRC 1996a:102). Due to the population density in the basin, the control and care of the liquid emptying of combined sewage and handling of garbage are of high-priority. Of the 21 municipalities that conform the basin of the Cauca river, 19 municipal headtowns pour their domestic waste water in the river without any type of previous treatment. In 1997 polluting loads of 437.2 ton/month were contributed to the river, this expressed in terms of DBO5 and 548.7 ton/month of SST. Likewise, none of these municipalities has systems of final disposition of solid residuals. 85% of the industrial sector seated in this region contributes with 4.6 ton/day of DBO5 and 2.1 ton/day of total suspended solids (SST), which result of the productive processes of the Cauca and La Cabaña sugar mills and the Propal Plant (paper industry) II[1] (CRC 1996a:102).

Between 1987 and 1992 the forest area in the basin decreased from 14.1% to 7.2. In the area of influence of the Salvajina dam, the firewood consumption for several activities is of 28.800 m3 per year. Of the 197.600 hectares of the area of direct influence of the Salvajina dam, 13.400 hectares are from moderately to severely eroded and 2.297 hectares range from severely to very severely eroded. This situation has been worst due to the use of non-sustainable agricultural activities that have increased the sedimentation of the reservoir to levels of 1.400.000 tons per year. These activities have generated contamination due to the use pesticides (malatión, lorsban, sistemin and metil paratión), that greatly surpass the limits allowed by the Ministry of Health (CRC. Universidad of the Cauca 1996).

The projected supply of water for Caloto, Corinth, Padilla, Puerto Tejada and Santander indicates that the availability of water in this zone for the year 2.015 must be of 615 L/s, without keeping in mind the demands of the industrial development generated by the Law of Paez. Further more, it is necessary to add the quantities of the necessities of the sugar cane sector calculated in 2.83m3/s (ASOCAÑA 1998:159) and those of the industrial sector which are of 4.76m3/s (Torres 1998:105). This indicates that the environmental management of this basin is vital for the development of Cauca.

In this scenario, the potential use of the underground water is a very important alternative for satisfying the demand. However, the contribution of this resource has not still been determined. As a consequence, the urbanization processes, the handling and management of sewage, the pruning and deforestation are critical components that should be analyzed because of the potential synergism of the interactions that are propitiated in the basin.

The marked deforestation has generated the loss of the superficial land protection, this generates the alteration of the ground and increases its temperature because of the loose of the protection. The sunstroke increases, accelerating the vaporizing of the nutrients; as a consequence, the productive capacity of the land decreases with the alteration of the physical and chemical characteristics of the ground, this changes of the relationship plant-floor. So, the indiscriminate pruning will increase the erosion possibilities (Figueroa et to the one. 1998:30). This process carried out by man is affecting the aquatic ecosystems and causing the loss of river side zones that contribute with new energetic material that allows the primary production. Man activities in Cauca's basin have affected its appropriate course when intervening the fluvial dynamics of the river in detriment of the quality of the water and altering the traverse and longitudinal zones of vegetation and the fluvial landscape. These effects are worse in the low land area, located to the North of the Department, where the river generates bigger risk and dramatically affects the riverside community.

Basin of the Patía river

This basin has an extension of 542.065 kilometers. Its 221.083 inhabitants (20.0% of which are located in the urban centers) are the 20.2% of the population of the Department. The Patía river originates in the foothills of the Sotará volcano, which is 4580 meters high, and owes its formation to the confluence of the Quilcacé and Timbío rivers that unite in El Hoyo, at an altitude of 600 meters and a distance of 57 kilometers from its origin. The Patía river has an average flow of 139 m3/seg, equivalent to an output of 26.2 L/s/km2, in an extension of 5.420.65 km2. The transport of silts by the rivers is calculated in 17 kton/daily, that is to say, 3 t/day/km2 (CRC 1996b:30).

The micro-basins that integrate the upper basin of the Patía river in the Department of Cauca can be seen in table 1. Patía river I refers to the following micro-basins:

NAME AREA (ha.)
Timbío River 84.000
Quilcacé River 61.000
Guachicono River 98.000
San Jorge River 88.000
San Bingo River 59.980
Sajandí River 20.040
Mamaconde River 17.446
Mayo River 7.456
Patía River I 65.800
Patía River II 40.343

TOTAL 542.065

Table 1. The names for micro-basins that form the basin of the Patía river are: the Luna, Criollo, Capitanes, Cascajal, Versalles, La Cañada, Mamaconde (Picture 4) and El Salado basins in the Municipalities of Patía and Balboa. Patía river II includes the micro-basins of the Pinche, Yeguarizo, Martin Pérez, El Placer, Cañaduzal, Sánchez, El Zorro, Sachamates, Cangrejos, Mojarras, Casasapos, El Silencio, Matacea and La Despensa rivers. These micro-basins are shared by the departments of Cauca (56.27%) and Nariño (43.73%) (DNP-CORPONARIÑO-CRC-GTZ 1993:35-39).

As for total hydric source in the 14 sub-basins that constitute the basin of the Patía river, 91 micro-basins have been identified, of which 54 have been appraised, this means a covering of 59.3%, whereas the minimum flow in each micro-basin has a readiness of 2607L/s. The contributions of pollutant loads to the basin of the Patía river are represented, mainly, by domestic sewage of the municipal headtowns of Patía, Balboa, Bolívar, Merchants, Sotará, Almaguer, Florence and Timbío. These polluting loads have been considered in 62.3 ton/month of DBO5 and 7.75 ton/mes of SST (CRC 1996b:30). Except the municipality of Bolívar, the municipal headtowns of this basin do not have an adequate system of final disposition for domestic solid residuals. Also, the hygienic conditions of the slaughterhouses and the precariousness of the disposition of excretes at rural level reflects the inadequate state of basic infrastructures and of the wrong sanitarium handling of the region.

In this basin exist two pre-quaternary and quaternary aquifers having volumes of 46.619.000 and 25.357.000 m3 of water (DNP-CORPONARIÑO-CRC-GTZ 1993:35-39). Also, along the rivers Patía, Mayo, Guachicono (Picture 5) and San Jorge exist narrow alluvial plains with recent alluviums that can contain aquifers of high permeability, the same as those found in the Patía river composed by clays, sands and gravels with a maximum thickness of 20 meters and that have free aquifers with a possibility of transference of 700m2/d (Angel 1991). Free aquifers can also exist, semi-confined and confined associated to the Galleon formation (Angel 1991). The current demand of water in the area of the basin is estimated in 248L/s and in the projections for the year 2007 the inferred demand will be of 327L/s for a readiness of 150 L/inhabitant/day (DNP-CORPONARIÑO-CRC-GTZ 1993:35-39).

The lack of water in some areas and seasons of the year is evident [2], this situation has increased and has been directly related with global climatic phenomena such as El Niño, worsening the deficiency given by the alteration of the natural processes of regulation of river flows as a consequence of the loss of the protector vegetable covering. These environmental alterations favor the occurrence of erosive problems in the ground, which are more evident in the hillside areas of the oriental flank of the Western Mountain range, in the sub-basins of the Capitanes and Sajandí rivers.

The primary vegetation of the basin of the Patía river is almost extinguished due to the decrease of the forest areas because of the establishment of extensive cattle raising, agricultural parcels, illicit cultivations, population pressure and extraction of wood for construction, commercialization and other needs. In the Macizo Colombiano, where the basin of the Patía river has its origin, patches of native forests and areas with vegetation of moor can be found and require to be protected. The native forest has been very affected for the practice of pruning, burning and the establishment of illicit crops in the upper area of the region, the same as for the forest fires in the middle and lower part of the basin. These fires are generally associated to cultural practice. Another unbalancing factor of the environmental conditions is related with the mining exploitations; the environmental impacts caused by the handmade extraction of alluvium gold have degraded basins as important as that of the San Jorge river. These depredating processes have molded the geomorphic and biological standards of this basin and have affected the basic components to guarantee its sustainability such as the ground and the vegetation, thus, altering the intrinsic relationships of the system and affecting the readiness of water.

Cattle raising has affected land in a particular way, more than in any other region of Cauca, destroying the vegetal A00 horizon and generating, as consequence of the trample of the livestock, a compacting process in the horizon A1. This favors the loss of interstitial spaces, altering their permeability. This fact increases the superficial (water draining) escorrentia and alters the relationship ground-plant as for the readiness of water, affecting the vegetative processes, and changing the relationship of the productive capacity thus increasing its susceptibility to the erosive processes. The destruction and loss of the A00 horizon has generated an increased in the sedimentation, which is expressed in an increment in the turbidity of the natural waters and a change in the biological demand of oxygen, propitiating alterations in the physical and chemical characteristics that can produce changes in the composition of the communities and alterations in the primary gross productivity (PPB) of the aquatic ecosystems. The cattle activity in the basin is associated with the change of use of the land, changing the forest areas into pastureland. This conversion brings an interruption of the succeeding process that potentially damages the horizon A00 and generates the loss of habitats and niches, securing the ecosystem fragmentation and generating the loss of endemic elements. This situation is expressed the alteration of the fauna and flora diversity and in the cavity of the niches, what means alterations of the intra and inter-specific relationships, favoring thus the competition among individuals of the same species and among different species, altering the trophic chains and affecting the biodiversity of the system (Figueroa et to the one. 1998).


Pacific basin

The basin of the Pacific occupies 10.271.95 km2, 34% of the total area of the Department, and includes the municipalities of Guapi, Timbiquí, López de Micay, Algeria and 60% of El Tambo. In this region 106.112 inhabitants live, 9.73% of the population of the Department, 18% of which is concentrated on its municipal headtowns and riverside areas. The Micay river (Picture 6) contributes with an average flow of 606 m3/s, corresponding to a contribution of 155 L/s/km2, while the Naya river contributes 417 m3/s, the Saija river 166 m3/s, the Timbiquí and El Buey rivers 147 m3/s and the Guapi-Guajuí river with 357 m3/s (Mejía et al. 1984).

This basin is important for its hydroelectric power possibilities, as well as to be the basin on which has been sought to develop a terrestrial communication with the Pacific ocean. Apart from these reasons the Natural National Park of Munchique, can be found there, which is a natural reservation of world importance for its great biodiversity and because it constitutes a great biological corridor if this park is connected with the Natural National Park of the Farallones through the basin of the Naya river. Given the hydrological importance of the basin of the Pacific, in Table 2 we point out the main tributaries of the Micay river, indicating the areas of their contributing basins and the longitude of each bed (CRC-University of the Cauca 1992:140).

Basin Area (has.) Longitude (kms)
Micay 156.280 100.0
El Tambor 10.555
Murciélago 5.096 19.5
La Iguana 14.714 31.5
Isla de Gallo 4.555 12.3
Chuare 64.669 50.9
Siguí 12.957 28.6
Aguaclara 19.412 27.9
San Joaquín 27.643 40.2
Jolí 6.076 18.9
Mechengue 20.373 31.8
End-Mecaje-Huisitó 47.016

San Antonio 8.250 19.5
Plateado 12.404 27.5
Guaitara 3.000 17.1


Table 2. Main tributaries of the Micay river.

The underground waters in the littoral of the Department of Cauca are related with the geologic characteristics of not consolidated silts existing in the deltas of the Naya, Micay and Guapi rivers, the same as the coastal alluviums of great part of the coast that have aquifers having two types of variable extension: coastal and continental. The first ones are water springs of fresh water that lie on and are surrounded of salt water; the theoretical projection of the springs of fresh water is 40 times the elevation of the water chart. The continental aquifers are quite far from the coast and they have a direct relationship with the superficial currents that drain from the Western Mountain range (INGEOMINAS 1989).

In this basin the main source of contamination of the currents of water is especially related to the processes of auriferous exploitation, more than to domestic sewage in the municipal headtowns. The polluting load can be considered in 6.707 kg. / month DBO5 and 7.985 kg. / month of total suspended solids (SST). This last figure is mainly related with the coconut processing industry and the activities of wood transformation. In the municipal headtowns there is not a systems of final disposition of domestic solid residuals and the covering of the sewer system in these cities is only of the 50%.

Apart from this environmental problem, very bounded to the basic drainage, serious problems generated by the traditional mining form exist. This atrophic activity, together with the pruning processes, are the more devastating and determinant factors for the environmental future of the Pacific zone of Cauca's Department. When analyzing the relationships and the traditional processes of the mining activities, three types of exploitation should be differentiated: open cut, underground, and alluvial exploitations; this last one is carried out in the river beds and in the alluvial terraces, not only generating important impacts caused by the extraction but also for the prosecutions. This type of exploitation is causing the destruction of the horizons of the ground, generating topographical and geomorphic changes that contribute to the instability of the land and leave without funds rock formations, what increases the processes of weathering of the rocks because this intensifies their oxidation and their exhibition to higher temperatures and accelerates the diaclastic processes. These conditions favor processes like the leaching out of nutrients which is produced by the alteration of the floor in its physical and chemical characteristics; and the escalation in the mineralizing processes, what accelerates the leaching out processes, diminishes the productive capacity of the land, thus increasing erosion. The loss of vegetable covering as a consequence of the destruction of the horizons interrupts the succeeding processes and propitiates the habitat loss and niches, originating the displacement of terrestrial and aquatic fauna; this fact favors the lap of niches and it reinforces the intra and inter-specific competition, inducing the migration of species, altering the fauna diversity and vegetation and, even, propitiating the endemic loss (Figueroa et to the one. 1998). The hydric resource is affected by the destruction of the horizons and the deviations of the river beds; this generates sedimentation and turbidity for solid residuals and emptying of the mining camps, causing the change in the physical and chemical characteristics of the aquatic ecosystems.

All these activities transform the landscape, empowering the loss of the river side areas and altering the productivity and the trophic net of the system. The most affected basins by this activity are those of the rivers Micay, Aguaclara, Timbiquí, Jolí, Naya, Guapi and Guajuí.

Basin of the upper Magdalena

Magdalena's river basin has its origin in the Macizo Colombiano, it is located at an altitude of more than 2.200 meters, with an approximate area of 155km2, an output of 105.71L / km2 and a flow of 152.93m3/s24. The main tributary of the Magdalena's upper basin is the Páez river that springs in the Northwest side of the snowy mountain of Huila. Among the rivers that empty in the right riverbank of the Páez river, are the San Vicente, Moras, Ullucos and Rio Negro rivers; the Ullucos river receives, in turn, the waters of the rivers Malvazá, Ovejas and Guanacas, which originate in the Delicias and Moras moors. By the left riverbank the Páez river receives the waters of the Toez, Símbola, Salado, Guelcar, Macana, Gallo, Honda and Totumo brooks (IGAC 1993:159).

The upper Magdalena's basin in the Department of Cauca is located in the municipalities of Páez and Inzá; the first one lodges 85% of the indigenous population which was hardly affected by the avalanche of the Páez river. The population of this basin is of 61.637 inhabitants, 5.65% of the total population of the Department; 4.28% of it is located in the municipal headtowns.35% of the rural population's lacks of basic sanitation services, which affect the quality of the hydric resource. The most critical situation can be seen in the indigenous reservation of San Andrés' and and Santa Rosa, and in the areas of Turminá, Pedregal, Itaibe, San Luis and Rio Chiquito. The polluting load of the Páez river that empties in the Magdalena has been considered in 6.510 kg. / month of DBO5 and 7.750 kg. / month of SST26, corresponding only to the domestic sewage of the municipal heads.

36.7% of the vegetable covering corresponds to native forest located in the oriental slope of the Central Mountain range, but it is being affected by colonization processes. Finally, the moor vegetation corresponds to 3.3% of the total of the basin.

Basin of the upper Caquetá river.

This basin is located in the Southeastern part of the department and it is known as the Bota Caucana, integrated by the municipalities of Santa Rosa and Piamonte. It is the most recently populated basin and that of lower population density; it only represents the 2% of the population (19.061 disseminated inhabitants in a 97% of the rural area of the municipalities).