Chapter 2. Water Quality System of Puerto Berrío
This chapter is oriented to a more detailed presentation of the characteristics of the water quality system of Puerto Berrío, including a description of the drinking water and wastewater system, characteristics of the receiving water body, going from a general overview of the river basin to a more detailed description of the river stretch where the municipality is located. Finally, the relation between the river and the municipality, and its influence on people’s life will be briefly explained.
Drinking water and wastewater management
The present section is divided in four subsections, starting with a brief description of the drinking water supply system and followed by some general remarks on the sewer system of Puerto Berrío and the wastewater treatment plants found there. Finally, the fourth subsection will present a detailed description of the wastewater discharges identified in the municipality. The information presented here was mainly obtained during a field visit to the study area and was complemented with the information found in documents such as the Development Plan and the Land Use Plan of Puerto Berrío. This information is of great relevance since it serves as a base for the upcoming chapters, where the local effects of the wastewater discharges will be analyzed.
Section keywords: water supply, sewage system, coverage, wastewater treatment plants, treated wastewater, untreated waste water, location, distances, amount
Drinking water supply system
The water supply service in Puerto Berrío varies from the urban to the rural area in coverage as well as in quality, being the urban area the most favored thanks to the concentration of the population. Currently, the company Aguas del Puerto S.A. provides the urban area with drinking water, taking it from the Magdalena River and giving it a conventional treatment to reach the desired and required quality for human consumption. In the urban area 100% of the population is covered with the service, with a supply of 150 l/s (Alcaldía Municipal de Puerto Berrío, 2008). Even though the coverage seems high, the distribution system presents a lot of deficiencies such as cracks, illegal connections, leaking, insufficient pressure, inadequate pipe diameters and inadequate storage capacity of the tank, causing water losses of around 50% (Alcaldía Municipal de Puerto Berrío, 2000). On the other side the water quality is very good and monitored continuously in the outlet of the treatment plant (see Figure 2).
The individual houses and spread settlements in the rural area make it difficult to provide a centralized water supply service and usually every settlement or group of settlements has different drinking water sources with inadequate distribution networks or none at all. In the rural area, only 64.8% (Alcaldía Municipal de Puerto Berrío, 2008) of the population is connected to a water supply system, and the drinking water doesn’t receive any kind of treatment before its consumption in just about all cases. Fortunately, the region is very reach in water resources and therefore there is good availability, but the quality is not always adequate for consumption due to unprotected (deforestation) or affected watersheds by anthropogenic activities. In the analyses of the drinking water quality in the rural area, coliform bacteria have been found, which results in health problems of the population such as skin infections, diarrhea and gastroenteritis, especially in children under 5 years.
Archivo:Imagen:DSC00305 Copia.jpg
Figure 2. Drinking water treatment plant
Sewer system
The coverage in the sewer system presents a similar behavior to the drinking water system. The urban area is prioritized with a coverage of 82.5% (Alcaldía Municipal de Puerto Berrío, 2008), while in the rural area only very few settlements are connected to some kind of sewer system. Illegal connections to the system are frequent, increasing the collection of wastewater to almost 90%, according to the land use plan (Alcaldía Municipal de Puerto Berrío, 2000). The sewer system of Puerto Berrío was built 50 years ago, initially for the collection of rainwater but later the wastewater was connected too, making it a combined sewer system with many hydraulic deficiencies due to under dimensioning. The amount of wastewater discharged by the municipality is approximately 120 L/s, based on a consumption of 150 L/s and a return coefficient of 80% (Ministerio de Desarrollo Económico, 2000). All discharges of the system flow into the Magdalena River or one of its tributaries without any treatment, except for a 3% (4 L/s) that are treated in a small plant called El Pensil. The current sewer system network is divided in four sectors: Barrio La Malena, Barrio Milla No. 2, Puerto Colombia and Centro (see Appendix A). As for the rural area and illegal settlements on the outskirts of the urban area, the wastewater doesn’t receive any treatment and is disposed into open channels (see Figure 3) or into the nearest water body, usually a tributary of the Magdalena River or the river itself depending on the location of the settlement.
Wastewater treatment plants
In Puerto Berrío there are three wastewater treatment plants: El Pensil, Lagunas and La Malena. By the time of the field visit to the study area in April 2008, only the first one was working. The treatment plant El Pensil (see Figure 4) is being operated since February 2007 and treats 4 L/s (Aguas del Puerto, 2007) with a removal efficiency of around 82% for BOD and 75% for COD and total solids. Lagunas (see Figure 5) is the newest treatment plant, but not being operated yet. Besides a primary treatment, the system will provide a biological treatment through three oxidation ponds, one anaerobic and two facultative. This plant was built to treat around 80% of the municipal wastewater, discharged currently untreated into the Magdalena River using a pumping station (data from field visit). The plant La Malena was built in 1997 for the treatment of the wastewater of 285 houses of the neighborhood under the same name. It was projected for 20 years, however the construction was never completed and the plant has never been operated (Alcaldía Municipal de Puerto Berrío, 2000).
Wastewater discharges
As noted in Section 2.1.2 the wastewater from the urban area in Puerto Berrío comes from four sectors and the production is around 120 L/s. According to the population distribution, the information obtained during the field visit and the land use plan (Alcaldía Municipal de Puerto Berrío, 2000) the wastewater production of each sector was estimated as follows:
- The sector called La Malena has a wastewater production of about 5 L/s and the discharge is done into the ravine La Malena, which flows into the Magdalena River approximately 4 km downstream of the urban area.
- The wastewater produced by the sector Milla No. 2 is 11 L/s, which represents 9% of the total wastewater production of the urban area. 4 L/s are treated in the wastewater treatment plant El Pensil, and the remaining 7 L/s are discharged into an open channel, where the plant discharges the treated effluent as well.
- In the settlement Puerto Colombia there are three wastewater collectors flowing directly into the Magdalena River. Moreover, due to its location and the lack of sewer system in some parts of the settlement, many houses that rise directly on the riverside discharge the wastewater individually into the river. The total discharge of this sector is estimated to be 11 L/s. (See Appendix B)
- The main discharge in Puerto Berrío comes from the sector Centro, where around 78% of the total wastewater is produced, i.e., 93 L/s. This wastewater doesn’t receive any treatment and is discharged into the Magdalena River by means of a pumping station to guarantee its adequate evacuation. The place of discharge is a settlement called Villas del Coral, on the outskirts of the urban area, limiting with the sector of Puerto Colombia. (See Appendix B)
In the rural area there are only few sectors that have a network system built independently from the one in the urban area. From the settlements of the rural area, only one, Puerto Murillo, is known to discharge the wastewater into the Magdalena River. The amount of this discharge is not known, but since the rural population is relatively small and this is just one of several settlements in the area, it can be assumed that the discharge is very small and can be neglected for the purpose of this study. The rest of the settlements in the rural area discharge the wastewater into various river tributaries and it is also frequent the discharge on land.
The situation in Puerto Berrío matches quiet well with the situation currently found in most municipalities of the Magdalena River basin. Figure 7 shows the general situation while Figure 8 shows an approximation to the specific situation of Puerto Berrío with respect to the wastewater discharges.
Figure 7. General scheme of municipalities on the Magdalena River basin
Fuente: Adapted from Cormagdalena, 2007
Figure 8. Wastewater discharges of the urban area
The flow diagram in Figure 9 summarizes the information presented in the past four subsections, describing the situation of the water quality affecting system in Puerto Berrío.
Figure 9. Flow diagram: current scenario
Regarding the characteristics of the wastewater produced in Puerto Berrío, an average of the parameters was calculated based on three different wastewater characterizations from 2005 (Aguas del Puerto, 2007) (see Appendix C), which presented similar values. Every discharge of the municipality is assumed to have these characteristics (see Table 1) and to be constant during the year.
Table 1 Wastewater characterization
According to the decree 1594 (see Section 1.3) the municipality is currently complying with only two of the six parameters regulated for wastewater discharged into a water body Table 2.
Table 2 Limiting values for wastewater dsicharges
Description of the receiving water body
As described in the regional and local background, Puerto Berrío is located on the riverside of the Magdalena River, and it has grown to the interior as well as along the river, which is used as receiving water body for most of the wastewater discharges of the municipality. The next subsections will give a brief presentation of some characteristics of the Magdalena watershed, including some general information on the river water quality and on the longitudinal and seasonal variations that are relevant for the present work.
Section keywords: river stretch, flow discharge, water quality, seasonal variations, POEM
The Magdalena River Basin
The size of the Magdalena River Basin is 199,294 km2, occupying 17% of the whole national territory (see light green region Figure 10). It has a length of 1,528 Km, from which 886 km are navigable, making it an important communication and transport route, both of them relevant aspects for the economy of the country. It rises in the south, at a height of 5,617 m above sea level and flows to the North, flowing into the Caribbean Sea. The population in the river basin is 20.8 million, which represents 49% of the country’s population . 17 departments and 557 municipalities are settled on the river basin, making its management quiet a challenge (Cormagdalena, 2007).
According to the bimodal distribution of the rain and the dry periods the river discharge also presents two low water seasons (see Appendix E). Though a natural behavior of the river, the low water seasons entail a series of problems such as limited availability in the reservoirs and drinking water intakes, restricted navigability due to very low water levels and erosion of the riverbed and riverbank (Cormagdalena, 2007). In the middle Magdalena region, the morphology of the river is mainly flat, with smooth undulations, meandered to the south and braided to the north. Some formations found here are flood plains and terraces, islets, swamps and abandoned channels. The islands, some of them very large, and spread channels are the more significant formations (Ingeominas, 1999).
Figure 5 The Magdalena River in Colombia
Fuente: Wikipedia
Figure 6 Departments in the Magdalena River Basin
Fuente: FFEM - Cormagdalena, 2007
Water quality of the Magdalena River
Water quality is defined by several physical, chemical and biological variables. Some of the physical variables are temperature, color, turbidity and suspended solids; to the group of chemical variables belong nutrients, minerals, metals, oxygen and organic compounds; and finally biological variables are those related to the type and quantity of aquatic plants, animals, algae, bacteria and protozoan parasites (Alberta Government, 2006).
In wastewater discharges the most important parameters to be taken care of are the dissolved oxygen (DO), the suspended solids, the coliform bacteria, the nutrients, the pH and the chemical toxic compounds, since they can affect the water quality of the receiving water body to a large extent. The importance of DO in the aquatic life is due to the harmful effect that very low DO concentrations (below 4 - 5 mg/L) can have on determined species. Suspended solids affect the turbidity in the water column and end up settling on the bottom, while coliform bacteria are an indicator that other pathogen organisms are present, and therefore determine if the water is safe for uses such as recreation or human consumption. Nutrients can cause eutrophication and reduction in DO levels. The acidity, measured as pH, affects the chemical and biological environmental equilibrium of the water, and the chemical toxic compounds, depending on their concentration, can harm human and aquatic life (Metcalf and Eddy, 1995).
In Colombia, the entity that carries out monitoring activities of the quality of the water resources at the national level is the IDEAM (see Section 1.2.2). As a result of these monitoring activities the IDEAM has generated surface water quality maps for the whole country, describing the status quo of the surface water resources regarding five parameters: temperature, pH, chemical oxygen demand, dissolved oxygen and turbidity. Based on these maps some information about the water quality of the Magdalena River, especially at the point where Puerto Berrío is located, was obtained.
- Temperature: the northern part of the Magdalena River basin shows temperatures between 25 and 30ºC and the rest belongs mostly to the category of 20 to 25ºC, including the municipality of Puerto Berrío. Water temperature is an important parameter to be considered when analyzing the suitability of the water body as habitat for living species. It also gains importance due to the fact that all chemical and biological process rates depend upon it (Orlob, 1983), and it has a strong influence on other parameters, such as pH, conductivity and oxygen deficit (IDEAM 2001).
Figure 7 Temperature of surface water in Colombia
Fuente: Ideam, 2001
- pH: the pH of the water defines to some extent its capacity of self-purification, and therefore its COD and BOD content. Common pH values in natural waters are between 6.5 and 8.5 (IDEAM 2001). The Magdalena River presents a pH of 6 in almost all its length, except for the most northern and southern parts, where it shows higher values.
Figure 8 pH of surface water in Colombia
Fuente: Ideam, 2001
- Chemical Oxygen Demand (COD): the COD measures the amount of dissolved oxygen consumed during the oxidation of organic and inorganic compounds in the water (IDEAM 2001). With regard to the Magdalena River, more than half of the river basin shows COD values between 0 and 20 mg O2/L and the rest shows values in the range of 21 to 41 mg O2/L. In Puerto Berrío, the COD was found to be in the latter.
Figure 9 COD in surface water in Colombia
Fuente: Ideam, 2001
- Oxygen Deficit: A parameter that is strongly related to the COD and the BOD (biochemical oxygen demand) is the oxygen deficit. It is a value that indicates the difference between the dissolved oxygen present in the water and the theoretical maximum value. This maximum value is determined based on the atmospheric pressure and the temperature of the place under study (IDEAM 2001). The higher the oxygen deficit, the lower the dissolved oxygen available in the water for the living organisms that depend on it. The Magdalena River presents the lowest oxygen deficit, 0 to 20%, in the southern part, and it increases in the middle and northern part, including Puerto Berrío, with values between 20 and 40%.
Figure 10 Oxygen deficit in surface water in Colombia
Fuente: Ideam, 2001
For a better interpretation of these values there needs to be a reference to which they can be compared. Water quality regulations are limiting values, quantitative and qualitative, defined with the aim of maintaining or improving the quality of the receiving water bodies (Metcalf & Eddy, 1995). A way of defining water quality is based on the requirements of a specific use, e.g. human consumption or aquatic life conservation. In Colombia, the decree 1594 (see Section 1.3) sets the standards to which water quality should comply according to the use to be given to it.
From the parameters discussed above for Puerto Berrío, only two are regulated by the decree 1594, namely pH and dissolved oxygen saturation. Based on the pH, the water from the Magdalena River is adequate for all uses. As for the dissolved oxygen saturation, is possible that the river does not meet the requirements for recreation in some parts of the region, since the deficit is in the range 20 to 40%. Table 3 shows these and other standards relevant to the present study, the blank cells are parameters not regulated for the specific use.
Table 3 Water quality standards of the Decree 1594
Another way of defining water quality is by means of indexes. Water quality indexes are calculated based on a combination and relation of parameters. The result of this calculation is then compared to a scale defining the water quality both quantitative and qualitative. Water quality indexes will be explained more in detail in Section 4.3.
Longitudinal and seasonal variations in the Magdalena River
Rivers undergo a series of water quality and hydraulic variations some of them caused by meteorological factors and some of them caused by the discharge of wastewater into the river and the processes taking place in it, that constitute the so-called self-purification capacity. For a better understanding of the general characteristics of the Magdalena River, its longitudinal and seasonal variations, especially regarding the vicinities of Puerto Berrío, will be briefly presented in the following sections. The simplified scheme in Figure 11 shows the river stretch in the Middle Magdalena Region, where Puerto Berrío is located, with some of the significant municipalities and tributaries and also with the existing data that will serve as a base for the coming sections.
Figure 11 Simplified representation of river stretch in the Middle Magdalena
In Figure 11 six different types of information are shown and they will be used for different analyses as well, some in this section, some in later ones. The river water quality data obtained by monitoring activities (IDEAM, 2007) (see Appendix G), will be used to present the longitudinal variation of the water quality, while the periodic monitoring data (represented by the yellow circle) (ISAGEN, 2008) (see Appendix H), will be used to show the water quality seasonal variations throughout the year, and the data from the limnigraphic station in Puerto Berrío (IDEAM, 2008) will be used to show the seasonal variations of the river flow and water levels.
Longitudinal water quality variations
River systems have physical and chemical characteristics that differentiate them from other water systems, such as lakes. In a river there is a predominant longitudinal movement of pollutants and other substances, which means that the length of the river is the most relevant aspect, while the vertical dimension can be assumed as homogeneous, therefore the river depth is not as relevant (Hahn, 2008).
These characteristics of the river influence the movement and transformation of the discharged pollutants. Many biological, chemical and physical processes are taking place along the system causing fluctuations in the various water quality parameters. The successive changes occupy different river reaches and establish a profile of pollution and natural purification, yet there is no set pattern in most streams. Instead, the pattern shifts longitudinally up and down the watercourse and is modified in intensity with changes in season and hydrography (Fair et al., 1968). The processes that take place in a river can be generally classified in two categories: transport processes, which have a similar effect on all water quality parameters, and transformation processes, which have a different effect depending on the constituent (Metcalf & Eddy, 1995). All processes will be briefly explained in this section, and some of them will be treated more in depth in chapter 3 according to their relevance. At the end of this section, the longitudinal variations found for the river stretch (see Figure 11) will be shown in various graphs.
There are two main transport processes taking place in a river, namely advection and diffusion. Advection is the transport of a constituent due to the water flow in which it is dissolved or suspended, and diffusion is caused by water turbulence and can also be described as a localized mixing phenomenon. Among the transformation processes, following are found (Metcalf & Eddy, 1995):
- BOD oxidation: The biochemical oxygen demand (BOD) is a measurement of the organic matter contained in the water that is biologically degradable. In order to be able to oxidize or degrade the BOD, the organisms in the water need to consume oxygen that is dissolved in it and therefore available. There are two types of BOD: the carbonaceous BOD, that is degraded in first place, and the nitrogenous BOD that is degraded 8 to 12 days after.
- Surface reaeration: is the oxygen net flux occurring between the atmosphere and a water body with a free surface and a concentration of dissolved oxygen below the saturation point.
- Sediments oxygen demand (SOD): Part of the solids contained in the water are organic. Once they sediment, a degradation process starts on the bottom, which can be aerobic or anaerobic depending upon the conditions. Under aerobic conditions, dissolved oxygen is consumed during this process.
- Photosynthesis and respiration: The levels of dissolved oxygen in the water can be affected by algae (e.g. phytoplankton) and macrophyte growth, whose source of nutrients are the ammonia and the nitrates. Under daylight conditions, these organisms release oxygen due to the photosynthetic processes. During the night instead, they respire, i.e. they consume oxygen. This causes short-term variations in the dissolved oxygen concentration, but in case of a loss of equilibrium, for example excessive algae growth, could turn into long-term variations.
- Solids sedimentation: the solids contained or discharged in the water have a natural tendency to sediment, however this process can be either favored or inhibit by other factors. In rivers for example, turbulence causes a distribution of the solids all over the water column. Sedimentation velocities are usually small.
- Bacteria mortality: is the velocity of disappearance of pathogen bacteria and viruses.
- Adsorption: it is the process of adhesion of chemical water constituents to solids.
- Volatility: is similar process to that of reaeration, but in this case the net flux goes from the water to the atmosphere, releasing some constituents such as volatile organic compounds (VOCs)
These processes are not individual and independent; on the contrary, as a natural behavior of any system, they present many interrelations affecting not only one water quality parameter, but also many others. As an example, water temperature affects the rate at which BOD is degraded, and at the same time BOD degradation affects the dissolved oxygen concentration in the river.
Between the municipalities of Puerto Boyacá and Puerto Wilches, the Magdalena flows through a distance of approximately 210 km. Along this distance, the river receives several discharges both from municipalities and tributaries. These contributions have usually a high organic load due to the lack of wastewater treatment plants in the municipalities. According to the Magdalena River watershed management plan (Cormagdalena, 2007) the organic loads discharged by the municipalities of Puerto Boyacá, Puerto Berrío, Barrancabermeja and Puerto Wilches are approximately 1,340 Kg/day, 1,712 Kg/day, 8,079 Kg/day and 748 Kg/day respectively. The following graphs (see Figure 12 to Figure 15) show the results obtained for some relevant water quality parameters in the river stretch during the monitoring activities carried out in 2006 and 2007.
Figure 12 Longitudinal pH and temperature variations
Figure 13 Longitudinal variation of DO and oxygen saturation
Figure 14 Longitudinal TSS and COD variations
Figure 15 Longitudinal nitrogen compounds variations
Seasonal water quality, flow and level variations
This section will give a brief presentation of the seasonal water quality and flow variations that take place in the Magdalena River and that affect the municipality of Puerto Berrío. The water quality variations are presented based on data obtained from the monitoring activities performed by the company ISAGEN (ISAGEN, 2008), which operates a power station 5 km upstream from Puerto Berrío (see Figure 11). The monitoring activities started in 2002 until the present, and the data available made it possible to obtain an average of the parameters for each month of the year. As for the river flow and level variations, the results are based on data collected at the limnigraphic station from IDEAM (IDEAM, 2008) (see Appendix E) located few meters before the port, in Puerto Berrío. These data were available from 1987 to 2003.
Figure 16 pH and conductivity seasonal variations
Figure 17 Dissolved oxygen and temperature seasonal variations
Figure 18 BOD, COD and total solids seasonal variations
According to Fair et al. (1968), the intensity of pollution tends to rise during warm and sunny seasons and at low river stages, while it is suppressed during cold and overcast weather and when the stream is in flood. Looking at the previous graphs, an opposite behavior to this statement is observed. The BOD and COD show increasing values during the high water seasons, leading to lower values in the DO concentrations (see Figure 17 and Figure 18), i.e. around May and October. The reason for this contradiction is due to the fact that in the case of Puerto Berrío the seasonal variation is not related to temperature changes but to precipitation amount (see Figure 19, Figure 20 and Appendix E), so the statement does not completely apply to the situation. Another reason for the worsening of the water quality during the high water seasons is the abundant solids transport, which increases the turbidity and the organic matter content in the water. A clear relation between the total solids and the organic matter content is also seen in Figure 18.
Figure 19 Mean temperature in Puerto Berrío
Figure 20 Mean precipitation in Puerto Berrío
As for the seasonal flow and level variations in Puerto Berrío, they both show a very similar behavior, with a bimodal distribution directly related to the precipitation patterns of the region. The low water or low flow season can be easily identified in two periods of the year, namely between January and March and July and September. On the other hand, the months with the higher flows and water levels are May and November (see Figure 21 and Figure 22).
Figure 21 Seasonal flow variations
Figure 22 Seasonal water level variations
The annual mean flow for the period 1987-2003 in Puerto Berrío was 2,140 m3/s, and the annual mean water level for the same period was 3.7 meters. For the determination of the water levels, the lowest elevation of the riverbed at the measuring point is taken as a reference point. In Puerto Berrío, this elevation is 104.47 meters above sea level (Alcaldía Municipal de Puerto Berrío, 2000).
Water quality, flow and level seasonal variations play an important role when analyzing the impact of wastewater discharges into a river. On one hand, the water level determines if the pipe, according to its location, discharges the wastewater to the open air or submerged. This is the case in Puerto Berrío, where the low flow seasons are critical periods because the water level is not high enough to cover the outlet of the pipes and the wastewater is then discharged on the ground and flows into the river, where it is finally diluted (see Figure 23). The level is then related to the mixing zone. When discharging wastewater into a river a fast mixing is desired, especially for reducing the toxicity of some chemical compounds (Metcalf & Eddy, 1995)
On the other hand, pollutants assimilation does not only depend on the water level and the mixing zone. Desirable conditions of the water body are maintained when its volume and quality remain in balance with the volume and strength of the wastewater discharge (Fair et al., 1968). The available dilution flow is crucial in the wastewater discharge process. The dilution flow refers to both the quantity of water that is available for the dilution of the wastewater, and the quality of the water. Depending on the flow, the concentration of the constituents of interest in the receiving water body, and the desired water quality to be maintained, the capacity of a water body to assimilate discharged pollutants can be determined.
Figure 23 Seasonal water level variations in Villas del Coral
River stretch characteristics
Section Keywords: Aerial photograph, google Earth image, city plan, detailed sketch with river stretch dimensions, identified point sources, river flow, etc. Water quality data for the stretch and characterization of the discharges.
After having presented the general characteristics of the receiving water body, this section will be focused on a more limited part of the river, namely the river stretch that flows directly in front of the urban area of Puerto Berrío and the branch downstream, where the previously identified point sources are discharged. For a better description of the river stretch three reference points were selected, whose characteristics are assumed to be representative for each segment under study. The reasons for choosing them were the available data and the relevance with regard to the wastewater discharges. The first reference point (0) is located few meters below the bridge; the second reference point (1) is the first part of the branch of the river formed by the islets in front of the settlement of Puerto Colombia; and the third reference point (2) is the second part of the branch, formed by another islet downstream of the urban area. (See Figure 24).
Figure 25 locates the reference points in the river map and profile and gives an idea of the morphology of the riverbed and the formations found in the river stretch. The reference point No. 2 however, is not shown in the river profile, since it is assumed to have riverbed characteristics different from those of the main river. For this reason, the same riverbed elevation from reference point No. 1, was adopted. Table 4 shows the general characteristics of all reference points.
Figures 24 River stretch in front of Puerto Berrío Source: Google Earth, 2008
Figure 25 River stretch map and profile Source: Ministerio de Transporte, 1994
Table 4 General characteristics of the river stretch
Further on, the present study will be focusing only on the reference points No. 1 and No. 2, namely the branches of the river where the two wastewater discharges were identified, however due to the lack of data for this part of the river, it is necessary to take the reference point No. 0, from which enough data were available, as a base for calculating some of the other values, such as flow, water level and water speed during the high and low water seasons. As an extreme scenario of low water, the minimum flow and level measured in the last 20 years was taken as a base (see Appendix E). For these estimations, the river was assumed to be a trapezoidal channel (see Figure 26). The results of the calculations are displayed in Table 5 (see Appendix F).
Figure 26 Trapezoidal Channel
Source: Adapted from Chapra, 2007
Table 5 Seasonal variations in river stretch hydraulic characteristics
Regarding the water quality in the river stretch Table 6 presents the seasonal variations of several parameters. For the high water season, data from Aguas del Puerto S.A. (2007) was available, while for the low water season, data from the Company ISAGEN (2008) was used (5 Km upstream) assuming that the water quality does not vary significantly between the measuring station and Puerto Berrío. For the extreme scenario, the quality was assumed to be the same as in the low water season (see Appendix H).
Table 6 Seasonal variations in river stretch water quality
Section keywords: water withdrawal, drinking water treatment plant, raw water supply (informal), sand and other material extraction, recreation, fishing, navigation, public health.
The people in Puerto Berrío have a very strong relationship with the Magdalena River. It influences their culture, their economy, their environment, their sanitation and their living style. It is a referent in the region and as such there are many different river related activities carried out. Starting with the economic activities, the navigation, mainly for freight transport, is the most important one when speaking on a larger scale. It is the base of commerce and other business in the region and to a large extent in the country. Going on a less large scale, the river is also an important communication way among the nearest municipalities on the riverside. Other two economic activities carried out in the river at a local scale are the fishing and the sand extraction (see Figure 27). They can be considered informal activities performed by the people in order to make a living out of it and hence the conditions are not the best.
Figure 27 Sand extraction in Puerto Berrío
Figure 28 Pipe outlet at sand extraction point
With regard to sanitation aspects, an important service of the river is the supply of water for drinking and other domestic purposes. Even though it might not be the ideal drinking water source due to the load of pollutants it receives along its path, in Puerto Berrío the river water quality is still under the limits that allow its use for human consumption, after receiving the appropriate treatment. Besides, it is a reliable source due to the large water flow, even during the dry seasons. However, not all the water extracted from the river for human consumption or other domestic uses receives the adequate treatment. Due to the spread and increase of illegal and informal settlements, the current water supply system does not meet the necessities of many people in the municipality, leaving them with the only choice of taking the water from the nearest water body, in this case the river (see Figure 29). Also for Puerto Berrío and many other municipalities on the riverside, the Magdalena river serves as receiving water body for the discharge of treated and untreated wastewater and in some parts even for the disposal of solid wastes. The wastewater discharged into the river is then diluted and transported downstream while the river undergoes a self-purification process.
Last but not least, the river is used for recreation purposes such as tourism and bathing, and it is part of an ecosystem that provides habitat for many flora and fauna species.
Figure 29 Informal water extraction in Puerto Berrío