Erosion and Sedimentation in the Pacific Rim (Proceedings of the Corva l l i s Symposium, August, 1987). IAHS Pub l . no. 165.

Erosion and sedimentation issues in Peru

CARLOS A. LLERENA Depto. Manejo Forestal, UNA La Molina, Apdo. 456, Lima 100, Peru

ABSTRACT Erosion and sedimentation are common problems in Peru's coastal, highland, high jungle, and low jungle regions. The highlands and high jungle are the regions with the most serious problems due to their physiographic climatic, and socio-economic characteristics. Main problems in these regions are rill, gully,and mass erosion. Promising solutions are based on local traditional technology: terracing and agroforestry. Teamwork of Peruvian and external institutions keeps research and extension projects going. Because of the magnitude of the problem, new projects are needed. Some specific topics needing more attention are management of steep lands, landslide research, and erosion and sedimentation processes in jungle watersheds.

INTRODUCTION

Located along the west central coast of South America (Fig. la), Peru extends from the Equator to about 18°S latitude and approximately from 69 to 83°W longitude. The present Peruvian population is close to 20 millon. The total country area is 1 285 216 km2 (500 000 mi2). The coast line is about 2000 km long (1,250 mi). Peru's main sea and land features are two oceanic currents, the cold Peruvian or Humboldt current and the warm El Nino current; the Andean Mountains; and its tropical location. These features influence erosion and sedimentation. Also, these geographical characteristics clearly divide the Peruvian territory into four natural regions: coast, highlands, high jungle, and low jungle (Fig. lb,c).

Erosion and sedimentation are severe problems in Peru. The most serious problems are found in the highlands and high jungle. The seriousness of the existent erosion problems in Peru and their consequences for land and water uses contrast with the situation in ancient Peru. Pre-Inca and Inca cultures were skillful in land use and water management and were self-sufficient in food production.

This paper deals with erosion and sedimentation issues only of the highlands and high jungle.

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Erosion issues in Peru 5

EROSION AND SEDIMENTATION ISSUES

The highlands

General characteristics This region covers 30% of Peru's total area and sustains 40% of the Peruvian population, most of whom are poor peasants. In these lands of steep slopes, narrow valleys, and high plateaus with 39 peaks exceeding 6000 m elevation, the carrying capacity of land has been exceeded. Necessity pushes the people to cultivate slopes steeper than 50% at high altitudes. Here 1.6 million hectares are under cultivation at altitudes exceeding 2000 m. The upper limit of agriculture is found at 4200 m. The puna above this limit up to 4800 m are pastures for the Andean camelids and sheep. At 3400 to 4500 m it is still possible to find small relic forests mostly of quinual (Polylepis sp.), a tree adapted to high elevations. Groves of this species commonly dotted the highlands in former times, but because of the demand for cooking and heating fuel they now exist only in areas of difficult accessibility.

In this region there are differences between the north and south of Peru. The northern part, 150-250 km wide, is characterized by lower elevations, warmer and wetter lands. The southern area with widths up to 500 km accommodates broad, high-altitude valleys and plateaus collectively known as the Altiplano. This plain, lying above 3660 m, includes all southern, densely populated, mountainous Peru and incorporates the extensive Lake Titicaca basin at 3811 m elevation, stretching into Bolivia. Colder and drier than the northern sierra, much of the Altiplano is a desolate steppe. However, at lower altitudes agriculture is possible.

The major variables affecting climate of the Peruvian Andes are the massive, high-elevation mountains interacting with large air masses, and the interaction of latitude with altitude. Mean annual precipitation ranges from 300 to 900 mm. Seasonal temperature changes are modest, but diurnal temperature variation and the frequency of frost are significant. Both increase with increasing altitude.

The problems The erosion problems in the Peruvian highlands have been considered "among the worst in South America" by Zerbe et al. (1980). The main problems are rill and gully erosion as a consequence of short-term, high-intensity storms on bare soil disturbed for agricultural purposes, or by overgrazing, deforestation, mining, or acid rain. Estimates from 1000 to 2000 t km" year" of soil loss are reported by Low (1967) for this region. Guzman et al. (1966a) indicated that soil conservation problems in this region were mainly due to the existing agrarian structure. Ledesma (1971) presented some erosion control alternatives adaptable to the Mantaro Valley in the central Andes. Also, he indicated that land tenure characteristics in this area were obstacles for effective erosion control practices. For the same Mantaro region Paulet (quoted by Posner, 1982) obtained USLE's R values ranging from 100 to 200 (metric). Felipe-Morales et al. (1979) presented quantitative experimental results for this region using runoff plots. They found 5 t ha" year" to be the highest soil losses on agricultural lands with 25% slope and 768 mm of rainfall. Sedimentation in Lake

6 Carlos A.Llerena

Titicaca was studied by Boulange (1981). His results showed a settling velocity of 0.5 mm year . Quantitative measurements were also obtained by Rizo (1985) in the community of Chaute at 2300 m elevation, located near Lima.

In the puna, overgrazing and droughts combine to increase erosion risk. However, resilience of these lands maintains soil cover. On local areas peat soil mining for fuel and horticultural purposes, vegetative soil cover destruction by industrial pollution,and acid rain are potential threats where no reclamation measures are applied.

Also, mass erosion is an active seasonal process of variable intensity depending on rainfall patterns or other triggering events like earthquakes. In the unstable Peruvian highlands large avalanches and landslides have caused dramatic destruction and a high number of casualties (Plafker & Ericksen, 1978; Plafker & Eyzaguirre, 1979). The largest rockslide and debris flow historically recorded in the western hemisphere occurred in the Mayunmarca region on the River Mantaro, central Peruvian highlands, in April 1974 (Kojan & Hutchinson, 1978). Besides these large and rather uncommon events, minor ones occur seasonally, blocking roads and rivers, increasing sediment loads to peak levels, and generating numerous on-site and off-site problems. Studies about these less spectacular but hazardous processes are scarce. One of these studies by Morales-Arnao et al. (1984) reported eight landslides around the Tablachaca Reservoir which is part of the hydroelectric development of the Mantaro River. This facility produces 60% of the electrical power supply to Lima and central Peru.

Actual and possible future solutions Due to pressing socio­economic and political problems, this region presents the largest number of programs dealing with erosion and sedimentation.

Reforestation has been the main means of restoration of vegetation cover in the highlands. Suitable lands for reforestation in this region cover about 2.3 million hectares (Malleux, 1975). However, actual reforestation up until 1980 accounted for only 137 107 ha in Peru, 90% of which was in the highlands (Gutierrez, 1982). The main species used for reforestation are Eucalyptus globulus (95% of the planted area) and other Eucalyptus species, Pinus radiata, Cupressus macrocarpa, Polylepis sp., Caesalpinea sp., and Schinus molle. Species different than trees include tuna (prickly pear) Opuntia ficus-indica (Loayza, 1982). Several international funding agencies from Belgium, Canada, FA0, Netherlands, USA, and others support reforestation projects.

Projects including extension, demonstration, and communal participation are considered key activities in control of erosion problems in the highlands (Bochet, 1983). A nation-wide program for soil and water conservation under USAID support, mostly carried out in mountainous areas, is particularly successful in this matter (Chang, 1986). Programs of forestry education in rural schools, together with fuelwood plantations and general rural development by means of reforestation and forest utilization have been initiated lately with FAO/Netherlands support. The main aim of these programs is to make peasants aware of forest influences and that reforestation can be planned in an economically and environmentally profitable way (Kenny-Jordan, 1985; Romero, 1985; Jest, 1986).

Erosion issues in Peru 7

Probably the most promising projects for erosion and sedimentation control in this area are those oriented to recovering of traditional land use technologies. Some of these technologies are almost totally ignored by today's Andean people (Eckholm, 1975; Denevan, 1980; Jest, 1986). According to Dourojeanni & Molina (1983), historically the pre-hispanic Andean inhabitants considered three elements as being essential for proper land/water use: organization and community participation, the use of locally adapted working methods, and control over large amounts of vertical and horizontal land areas to allow various ecological levels to be managed simultaneously.

Extension and demonstration activities of local, traditional land use techniques are mainly oriented towards building and rehabilitating terraces. Donkin (1979) extensively describes agricultural terracing in the new world. Masson (quoted by Denevan, 1985), has recently estimated that there are more than one million hectares of terraced land in Peru. However, a major portion of these terraces is not currently cultivated, has been abandoned, and is in various states of deterioration.

Considering the potential for expanding the agricultural frontier in the highlands without increasing erosion and sedimentation risks, several terrace projects are underway in Peru and other Andean countries with the active support of several international agencies like IDRC, UNESCO, USAID, and others. Teamwork of Peruvian and foreign institutions, multidisciplinary effort, and local participation are common features of these programs described by Gishler & Fernandez-Jauregui (1984), Denevan (1985), Treacy (1985), Masson (1986), and Hawtin & Mateo (1987).

Watershed management as a concept (Hamilton & King, 1984; Richter et al., 1985) and as a practice is another possible way for controlling erosion and sedimentation. The Watershed Management Project carried out by the Directorate General of Water, Soil, and Irrigation (DGASI) has during 1981-83 developed programs of soil and water conservation in five basins of the central and southern highlands (Peru, 1983). The DGASI has since the 1970s, developed and supervised several local watershed management programs under different names. An extensive study of development programs during 1980-1985, including watershed management, is presented by Lopez et al. (1986). They pointed out the main constraints of these programs and suggested some alternatives for overcoming these constraints for the period 1985-1990.

The high jungle

General characteristics This zone begins with the transformation of the typical small, yellowish vegetation of the high mountains to greener, more abundant and taller plants in the upper misty forest, and ends at 600 m elevation, the upper limit of the low jungle. The high jungle covers 8.9 million hectares of rough terrain with soils mostly with no agricultural capacity. Nevertheless, it is possible to find fertile and flat alluvial soils, especially on the flood plains, that can be used for cultivation. Here the only limitation is seasonal flooding. Rainfall in this region averages 1000-7000 mm.

8 Carlos A.Llerena

In the last four decades this area has received an increasing number of peasants from the highlands. The occupation of these hilly forests for agricultural purposes has strongly increased in the last decade. Besides the spontaneous settlers, most of the government road and colonization projects have chosen this environment for developing new areas. Migration and associated land clearing have increased erosion and sedimentation problems in this region. The central high jungle is possibly the area under greatest pressure.

The problems According to Aramburu (1984) the migration of the Andean population into the high jungle began during the 1930s and reached its peak during the 1960s. This was linked to the expansion of commercial crops such as coffee, rice, fruits, coca, cacao, and tea. The consequences of the increasing land use are contradictory. The agrarian frontier expands in terms of land taken from the forest, yet land is lost through deforestation and erosion. Southgate & Runge (1986) presented a model explaining why the interaction of the aboriginal people with the outside world results in environmental degradation. They indicated that as logging companies or non-native agricultural colonists enter the Amazon and similar regions, indigenous inhabitants tend to abandon traditional systems of land tenure and adopt soil depletive techniques introduced by the new settlers. Dissolution of traditional tenure regimes results in abandonment of productive and sustainable farming systems. Also lost is aboriginal knowledge of management and use of tropical ecosystems. Often government settlement policies aggravate the situation.

Dance (1981) showed that 71% of the 5 million hectares deforested in the Peruvian jungle for agricultural purposes are located in the high jungle. A significant proportion of the cleared areas is classified as "protective forest" (Malleux, 1975). Dance (1981) estimated that the continuation of this trend would mean 8 million hectares of destroyed and fallow forest by the end of this century. Terborgh (1985) described the degradation of a high jungle valley. He pointed out that in 1965 nearly the entire region of the Apurimac Valley was in pristine condition, with virgin forest extending from the valley floor at 550 m elevation up the slopes of the ranges on both sides to timberline at 3500 m. After 18 years, he said, the scene has been irrevocably transformed. The region supported a population greater than 100 000 people, and not a trace remained of the majestic forest up to 1500 m in the slopes that had been cleared for coffee and coca plantations. Above 1500 m the forests had been pillaged for fuelwood and building materials. Gentry & Lopez-Parodi (1980) found that runoff and erosion increased as a consequence of land clearing.

Because rivers are the main transportation routes in the jungle, sediment deposition in channels is an important problem. Waterways that once provided efficient transportation are increasingly being choked with silt, losing their navigability, and becoming an unsafe and slower means of transportation. Native people living along the rivers Pichis, Palcazu, and Pachitea in the central jungle note that 30 to 50 years ago it was possible to reach upper parts of these rivers in larger boats than today. Hydrographical reports indicate as well that pioneer navy fluvial expeditions explored rivers that are now accessible only in small boats. Sedimentation limits

Erosion issues in Peru 9

navigation because of swift currents at high water and narrow and/or shallow sections at low water. Sharp bends and rapid siltation with growing bars and changing channel patterns are other difficulties (Sundborg & Rapp, 1986). There are few records of sediment loads in jungle rivers. Sediment load measurements have been made in the rivers Ene, Tambo, Maranon, and Amazonas for several years. In a study on the degree of forest disturbance caused by fluvial erosion, Salo et al. (1986) found that 26.6% of the low jungle has characteristics of recent erosional and depositional activity.

Low (1966, 1967) estimated erosion potential of this area at 5000-7000 t km'2 year"1 . Felipe-Morales et al. (1978, 1979) and Alegre (1979) measured soil losses on 30% slopes in San Ramon, using runoff plots under 1527 and 2027 mm of rainfall for the 1975-76 and 1976-77 growing seasons, respectively. They found that erosion rates vary from 2 to 148 t ha" year"1 according to the local erosivity and to the cultivation method used. Ruiz (1985) measured maximum erosion rates of 35 and 3 t ha"1 year" for grass and forest cover, respectively, in the Oxapampa region, central high jungle.

In addition to the problem of surface erosion generated by the destruction of soil cover, landslides are also common during the rainfall season. Slumps, not as spectacular as in the highlands but more frequent, are ubiquitous in roads of the high jungle each year. Location, construction procedures, and lack of proper maintenance of roads are frequently the cause of mass movements.

Actual and possible future solutions Soil classification and mapping efforts in the high jungle with the purpose of defining agricultural capability began in the 1960s after disastrous consequences of settlement failures were observed (Guzman et al., 1966). Unfortunately, not all subsequent projects benefitted from these past experiences. The idea of integral rural eco-development was applied to the high jungle in a proposal presented by Felipe-Morales (1979). The main objective of this project was to establish a pilot watershed in the high jungle for demonstration and research on proper soil, water, and forest resource management with multidisciplinary participation. This project was only partially completed due to funding problems. Suggestions for improvement of land use, forestry, and rural development in the Amazon through integrated resource management were presented by Dourojeanni (1981). A reforestation project carried out by the Peruvian Forest Service with support from a German funding agency (GTZ) began in the central high jungle in 1979 (Gutierrez, 1982). The main purpose of this project was to find suitable species and reforestation methods in this area.

Because of the "demographic vacuum" in the jungle, the constantly rising number of landless peasants in the highlands, and an increasing demand for food production, it would be unrealistic to suppose that forest clearance for cultivation will cease. However, it is possible to avoid many environmental problems. Several studies on better conventional farming methods in the Amazon Basin began with agreements between Peruvian and foreign institutions and universities (Nicholaides et al., 1985; Toledo & Nores, 1986). Nevertheless, in the high jungle it is recommended that conventional agricultural

10 Carlos A.Llerena

methods be used for food production only on the level, well-drained valley soils. This would leave the forest uncut on the sloping soils (Nicholaides et al., 1985). Additionally, on the valley soils under continuous cultivation, complete fertilization should be used in order to obtain a vigorous crop canopy and thus avoid surface soil compaction and erosion (Sanchez et al., 1983). Despite these considerations Fearnside (1987) criticized this approach.

Other non-conventional methods consisting of farming and forestry integration like the taungya system and agroforestry have been indicated by Dourojeanni (1980) and Myers (1986). The original models of these methods are found in the traditional technology of the native people (Posey, 1983; Denevan et al., 1984; Myers, 1986).

A research program developed by an international team and based at the Yurimaguas Experimental Station is working to improve the productivity of migratory agriculture using agroforestry techniques. The UNA and the University of Toronto are working in a research project on utilization of secondary forests that will assist in decreasing the pressure on deforestation of new areas (Dourojeanni and Hubbes, 1984). The National Peruvian Amazon University in Iquitos is also working on agroforestry systems. Studies by Padoch et al. (1985) showed that agroforestry, as a traditional jungle land use technique, is not only employed by tribal groups exclusively for their own subsistence. They presented a case of a successful, non-tribal market-oriented agroforestry business performed by "mestizo" farmers in the village of Tamshiyacu, located on the River Ucayali.

Terracing is also a suitable alternative for the high jungle. Sheng (1981, 1982) reported several applicable experiences in mountainous tropical lands including the combination of terracing with agroforestry.

SUMMARY AND CONCLUSIONS

Erosion and sedimentation are problems in each of Peru's natural regions. The most difficult are found in the highlands and high jungle areas due to their physiographic characteristics, high rainfall, and socio-economic complexities. Rill and gully erosion, as well as mass erosion, are active processes in these areas.

Efforts to alleviate this situation are now in progress. Both conventional and non-conventional land use systems are under examination and testing in the field. Extension and demonstration together with communal participation are key components of the programs aimed at control of erosion and sedimentation. Methods using traditional technologies in the highlands and high jungle are being implemented. Terracing in the highlands and agroforestry in the jungle are considered to be promising methods.

Research on and implementation of corrective measures are mostly performed by Peruvian and foreign institutions working together. However, given the magnitude of the problem and the urgency of the situation in some areas, larger and more active involvement of local and external agencies is needed. Particular problems like management of steep lands, control and prevention of landslides, and measurement of erosion and deposition processes in jungle watersheds have been neglected.

Erosion issues in Peru 11

Better coordination between agencies and researchers working on solving practical erosion and sedimentation problems in areas of similar conditions (arid lands, highlands, tropical rain forests), and sharing of experiences at national and international levels could accelerate research findings and improve land management. Development and support of programs like the FAO's Latin America Watershed Management Network, established in 1980, (Botero 1986) can facilitate this intention.

Awareness of the erosion and sedimentation problems must be stronger among politicians, planners, scientists, and the general public. When this happens, it will be easier to design better policies and programs to support efforts towards the solution of the problems. Expectations of a better quality of life for the rural people will be more feasible when this awareness increases and these policies and programs are implemented.

ACKNOWLEDGEMENTS I wish to thank my wife Bati and Veronica Delamora for typing and drawing. Editorial suggestions from M. A. Aleksiuk, P. Murphy, and C. R. Neill are much appreciated.

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