Water for people.pdf - WHO Thailand Digital Repository

L A K E T I T I C A C A B A S I N , B O L I V I A A N D P E R U / 4 7 1Oruro, bordering the eastern ridge. The approximate total volume ofgroundwater that goes into the system is 4 m 3 /s. Most of thisgroundwater comes from tube wells used to supply water to cities.Such is the case of El Alto, Oruro and several other small towns.Water table morphology shows that groundwater flows followthe direction of water reservoirs, the location of recharge areas andtheir base levels. The water tables of Huancané, Ramis, Coata andParco River basins on the Peruvian side, and Tiwanacu and CatariRiver basins on the Bolivian side, drain into Lake Titicaca withaverage hydraulic gradients of 1 to 0.1 percent.The optimum yield of aquifers and capacity in the Peruviansector range from 1 to greater than 100 litres per second, and from0.3 to 5 litres per second respectively. In the Bolivian sector,optimum yield ranges from 2 to 75 litres per second and specificcapacity from 0.3 to 4 litres per second.Water qualityThere are higher levels of salinity found in the south of the TDPSsystem, a result of greater rainfall in the northern part of the systemthat reduces the concentrations of dissolved salt. On the other hand,evaporation, which is greater in the southern part of the system,increases the concentration levels of dissolved salt. Thus, there is aprogressive increase of electric conductivity from north to south.Likewise, it is not uncommon to find tertiary and quaternaryformations, which are mainly present on the TDPS system, withparental material formed by rocks containing gypsum and salt.In general, Lake Titicaca and its tributaries have normal values ofwater salinity (less than 1,000 milligrams [mg] per litre). DesaguaderoRiver has values between 1 and 2 mg/litre, but downstream values aregreater than 2 mg/litre. Lake Poopó has salinity values above2,000 mg/litre due to natural conditions and mining activity in thesurrounding area. Maximum salinity values were found in Coipasa SaltLake where evaporation is high and rainfall is only 200 mm per year.Mining activity is the principal cause of heavy metal contamination,and is mostly found in the southern part of the TDPS system. Highconcentrations of arsenic are found at La Joya, in the western arm ofthe Desaguadero River. Lake Poopó as well as Coipasa Salt Lake presenthigh levels of lead, cadmium, nickel, cobalt, manganese and chromium.High values of faecal-coliform (1,000 parts per million [ppm])and organic matter throughout the Puno Bay are a good indicatorthat pathogens are present in the water. Those high values aremainly the result of wastewater from the Puno City sewer system.This contamination has generated a process of eutrophication andthe growth of aquatic lentils in the bay.Both water and fish from Lake Titicaca reveal high parasitelevels, probably due to inappropriate disposal of wastewater in thecities of Puno and Juliaca in Peru, and Copacabana in Bolivia, as wellas animal-raising and agricultural activities in areas surrounding thelake. The parasites infect humans as well, hence the high incidenceof gastrointestinal diseases.Extreme eventsMost extreme events in the TDPS system are related to flood riskconditions around Lake Titicaca, drought in the central and southernparts of the system and the incidence of hail and frost throughout(see maps 21.4 and 21.5).Human impacts on water resourcesSurface coverUntil approximately the year 1000, the high plateau was coveredwith a native tree forest (Polylepis sp). Around the year 1100, asevere eighty-year drought changed the surface cover and theforest disappeared. After 1500, inappropriate agricultural practicesand imported livestock permanently modified the conditions of thesurface cover. Over the last century, human activities have not had asignificant impact on the surface cover of the system in large partbecause of the arid environment and lack of vegetation.Dams and diversionsThe 6.37 metre variation between maximum and minimum registeredlake levels produced historical flood events in the lake andsurrounding areas. The Master Plan of the TDPS system (see furtheron for details) has required regulation works to be built thatmaintain the lake level at the minimum of 3,808 m.a.s.l. with amaximum of 3,811 m.a.s.l. during a normal hydrological cycle.PollutantsOrganic and bacteriological contamination is caused by human activity, inparticular urban wastes and mining. Poor waste disposal is the centralcause of organic contamination in all the important urban centres in thebasin. The most polluted areas affected by sewage discharge are Puno’sinterior bay (undergoing a moderate eutrophic process), the lowercourse of the Coata River, because of the discharge from the city ofJuliaca, and Lake Uru Uru, due to discharge from the city of Oruro.Heavy metal contamination is the result of mining activities inthe zone. Although there is not enough available information onthis subject, mercury and arsenic concentrations of 0.4 ppm havebeen found in mackerel captured in Puno Bay.Non-native speciesNon-native fish species with high economic value such as trout andmackerel were introduced into Lake Titicaca around 1930. Sincethen some native species such as karachi (Orestia sp) and boga(Trichomicterus sp) have decreased, and their populations areconsidered vulnerable and endangered.