Fig. 1   Proposed damsite on La Leche river at La Calzada.

LA LECHE RIVER FLOOD CONTROL PROJECT

LAMBAYEQUE, PERU

TASK 5:   ENVIRONMENTAL IMPACT ASSESSMENT

PART 7:   SECTIONS 10-12, APPENDIX, REFERENCES

July 24, 2009

Dr. Victor M. Ponce

Environmental Consultant

10.   MITIGATION STRATEGIES

Mitigation strategies and/or measures are planned and implemented with the objective to reduce, minimize, and/or neutralize the negative impacts that have been identified in the EIA. In some cases, mitigation measures will be effective in reducing the impact; in other cases, it may be difficult to reduce the magnitude of the impact. A few net losses are deemed an accepted compromise for the social and economic benefits to accrue from the project.

Table 41 describes a set of mitigation strategies for the EES parameters tagged with major red flags in Table 40.

Table 41.   Mitigation strategies for EES parameters with major red flags.
(1) (2) (3) (4)
No. EES parameter Description Mitigation strategies
1 Terrestrial browsers and grazers Affected fauna The reduction in the number of browsers and grazers due to reservoir inundation cannot be readily mitigated. One possibility is to designate alternate areas for grazing, to replace the areas lost to inundation. This is particularly significant in the case of Calicantro.
3 Terrestrial natural vegetation Affected flora The reduction in the number of specimens of natural vegetation cannot be readily mitigated. The loss of this natural resource is considered to be a trade-off for the economic benefits to accrue from the project.
12 Land use Loss of economically useful land The loss of agricultural lands at La Calzada and grazing lands at Calicantro must be appropriately compensated. This loss is considered to be a trade-off for the economic benefits to accrue from the project.
17 River characteristics Loss of swiftness of the stream The streams' natural characteristics will be lost once the reservoirs are in place. This will cause significant changes in the hydrobiology, both positive and negative. The loss of the swiftness characteristics of streamflow cannot be readily mitigated. It is considered to be a trade-off for the economic benefits to accrue from the project.
19 Basin hydrologic loss Decrease in runoff The project will cause a major conversion of runoff to evapotranspiration. This will cause increased salinity in the soil, imposing the need for additional drainage. This effect can be mitigated by reserving a certain portion of the natural runoff to carry the salts to the sea or, in this case, to appropriate sinks such as the La Niña lake.
28 Stream flow variation Reduction in flood magnitude and frequency The project operation will attenuate and reduce a significant number of floods. The effect will be both positive and negative; on the one hand, flood damages will be reduced; on the other hand, basin flushing will be compromised. This effect can be mitigated by a program of periodic artificial floods to reset the basin, partially emulating the work of Nature.
29 Temperature Increase in waterbody temperature Water will be retained in the reservoirs, and this water will gradually increase in temperature in the tropical local climate. This will change the hydrobiology of the waterbody. This effect cannot be readily mitigated.
30 TDS Increase in concentration of total dissolved solids The concentration of total dissolved solids will increase as water naturally destined to runoff is converted to evapotranspiration, leaving the salts behind. This effect can be mitigated with a program of agricultural drainage. A certain portion of the runoff must be reserved to carry the waste solids to the ocean or to an appropriate sink.


Table 41.   (Continued).
(1) (2) (3) (4)
No. EES parameter Description Mitigation strategies
41 Soil erosion Degradation downstream of dam The retention of sediments in the dams, particularly at La Calzada, will produce "hungry" water, which will have the tendency to pick up sediments as it flows downstream. There is a need for judicious sediment management to offset the negative effects of aggradation (above the dam) and degradation (below the dam).
42 Noise Increased ambient noise during construction Some noise will occur during construction. It is very difficult to mitigate this effect. The noise will abate as the project is completed.
45 Width and alignment Loss of view of the river The width and alignment of the streams will be markedly affected by the project. There is no way to mitigate this impact. The loss of this natural aesthetic resource is considered to be a trade-off for the economic benefits to accrue from the project.
55 Diversity of vegetation types Loss of species diversity The loss of vegetation diversity due to reservoir placement cannot be mitigated. The loss of this natural aesthetic resource is considered to be a trade-off for the economic benefits to accrue from the project.
56 Variety within vegetation types Loss of biodiversity The loss of variety within vegetation types due to reservoir placement cannot be mitigated. The loss of this natural aesthetic resource is considered to be a trade-off for the economic benefits to accrue from the project.
57 Manmade objects Loss of natural scenic view The reduction in aesthetics due to manmade objects cannot be readily mitigated. One possibility is to design them so that they are less obtrusive to the eye. To the extent possible, landscaping should be used as a way of providing a pleasing view of the facility and its surroundings.
62 Geological Loss of fossil resources The dams/reservoirs will flood land that is rich in paleontological resources. Efforts should be made to recover as much as these fossils as possible prior to the first flooding of the reservoirs.
77 Housing Loss of housing Local housing will be significantly affected by the project due to inundation. Compensation and relocation of the affected parties to suitable areas is a fundamental necessity of project development.

One bird species was identified as critically endangered (CE): the white-winged guan [pava aliblanca] (Penelope albipenis). The habitat of this species is the relic montane ecosystem, which is not directly affected by the project.

Three bird species were identified as endangered (EN): (1) the Peruvian plantcutter [cortarrama] (Phytotoma raimondii), (2) the rufous flycatcher [copetón rufo] (Myiarchus semirufus), and (3) the red-crown parrot [loro de cabeza roja] (Amazona viridigenalis). The habitat of the first two species is the floodplain ecosystem, which is not directly affected by the project. The habitat of the third species (red-crown parrot) is the Calicantro valley, which is directly affected by the project.

Two tree species were identified as endangered (EN): (1) the Andean walnut [cedro grande] (Juglans neotropica), and (2) the Peruvian sage [palo santo] (Guiaiacum officinale).

11.   ENVIRONMENTAL MITIGATION PLAN

The mitigation plan focuses on the following negative impacts which were identified in Sections 9 and 10:

  • Impact of changes in water flow due to dam operation.

  • Impact of changes in sediment flow due to dam operation.

  • Impact of changes in nutrient flows due to dam operation.

  • Impact of dam and reservoir construction on local fauna.

  • Impact of dam and reservoir construction on local flora.

  • Loss of agricultural lands due to reservoir flooding.

  • Loss of grazing lands due to reservoir flooding.

  • Loss of housing due to reservoir flooding.

  • Loss of runoff and consequent increase in salinity.

  • Loss of fossil resources.

  • Loss of switfness of the streams.

  • Loss of natural scenic view.

  • Increase in waterbody temperature.

  • Increase in noise during construction.

The environmental mitigation plan is shown in Tables 42 (A) to (N) (each table corresponds to each impact).

Table 42 (A).   Mitigation plan for impact of changes in water flow due to dam operation.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
A1.
Ecological discharge
 		1 Rationale A minimum ecological discharge must be maintained downstream of dam impoundments to assure the preservation of natural hydrobiological processes.
2 Methodology This ecological discharge should be developed based on local experience, but in no case should it be lower than 10% of the mean annual discharge.
3 Schedule The minimum ecological discharge should be maintained at all times, throughout the design life of the dam, estimated at 100 years.
4 Monitoring The regulated flow from the dam to the original stream should be monitored periodically to ensure compliance with the requirement of a minimum ecological discharge. The recommended monitoring interval is once a month.
5 Training One (1) civil/hydrologic engineer is required to assess the proper value of ecological discharge applicable to the La Leche river at La Calzada.
6 Human resources One (1) civil/hydrologic engineer, with field support personnel and logistical support.
7 Economic resources Low (less than U.S. $10,000 per year).

(1) (2) (3) (4)
Action No. Phase Mitigation plan
A2.
Recharge of groundwater downstream of dam
 		1 Rationale The aquifer downstream of the damsite (La Calzada) should be monitored to detect increased rates of replenishment, which could be attributed to an increased rate of infiltration at the damsite.
2 Methodology Baseline data prior to reservoir operation should be collected. A minimum of ten (10) observation wells should be placed in strategic locations along the La Leche river, from La Calzada to Bosque de Pomac. Unusual increases in water table levels, after start of dam operation, should be documented, and measures should be taken, if necessary, to return the water table to baseline levels through appropriate pumping.
3 Schedule Water table should be measured at regular intervals, not to exceed three (3) months. Seasonal variations should be taken into account in establishing the appropriate measurement schedule.
4 Monitoring Monitoring should be performed at regular intervals, not to exceed three (3) months.
5 Training One (1) hydrogeologist is required to assess and monitor the changes in water table which may be attributed to the reservoir presence.
6 Human resources One hydrogeologist, with support personnel and logistical support.
7 Economic resources Medium (between U.S. $10,000 and U.S. $50,000 per year).

(1) (2) (3) (4)
Action No. Phase Mitigation plan
A3.
Loss of basin flushing
 		1 Rationale There is a need to flush the basin at recurrent intervals, to simulate Nature's use of floods as resetting agents.
2 Methodology Artificial floods may be scheduled from time to time to flush the basin of sediments and other debris.
3 Schedule The schedule of artificial floods must be in consonance with the historic record of actual floods, which were not controlled by the dam and reservoir. In the absence of an actual flood, an artificial flood must be considered at least every five years, but no longer than every ten (10) years.
4 Monitoring Monitoring to assess need for basin flushing should be performed at regular intervals, not to exceed five years.
5 Training The training of one (1) civil/hydrologic engineer and one (1) river ecologist is required to assess the need for basin flushing.
6 Human resources One (1) civil/hydrologic engineer and one (1) river ecologist, with support personnel and logistical support.
7 Economic resources Low (less than U.S. $10,000 per year).

(1) (2) (3) (4)
Action No. Phase Mitigation plan
A4.
Risk of dam overtopping
 		1 Rationale The reservoirs, particularly La Calzada, must be operated to all but eliminate the risk of dam failure due to overtopping. This requires thoughful reservoir operation rules.
2 Methodology Operational rules must be developed to ensure that the emergency spillway is always able to pass the Probable Maximum Flood. For this purpose, the retarding-pool storage may be kept empty and ready for the PMF (Fig. 53).
3 Schedule Operational rules must be in place at all times to ensure that the emergency spillway is able to pass the Probable Maximum Flood.
4 Monitoring Eliminating the risk of dam overtopping should have the highest priority. For this purpose, the dam should be monitored on a daily basis, particularly during the rainy season, and more carefully whenever strong El Niño events are expected. During El Niño events, the objective of daily monitoring should be to ensure that La Calzada always has its retarding-pool storage empty and ready to store a large flood. Local experience may dictate that even active storage be reserved for very strong El Niño events. Conjunctive use of La Calzada and Calicantro may enable the use of La Calzada only for flood control, reserving most or all active storage for flood attenuation.
5 Training The training of one (1) civil/hydrologic engineer is required to develop operating policy, and to assess and monitor dam/reservoir operation to minimize the possibility of dam overtopping.
6 Human resources One civil/hydrologic engineer, with field support personnel and logistical support.
7 Economic resources Medium (between U.S. $10,000 and U.S. $50,000 per year).


Fig. 53   Storage volumes in reservoirs.

12.   SUMMARY

An environmental impact assessment (EIA) study of the La Leche river flood control project is completed. The project aims to enhance flood control and water conservation in the watershed of the La Leche river, which has suffered major floods caused by the El Niño phenomenon. The proposed actions are the construction of two dams, one to retain floodwaters and the other to store water for irrigation and domestic water supply. The flood-control earth dam spans a natural valley constriction at La Calzada. The seasonal and multi-annual storage dam spans the valley of neighboring Rinconada Calicantro to the west of La Calzada.

The environmental impact assessment is performed using the following two well-established methodologies:

  • the Leopold matrix, and

  • the Battelle Environmental Evaluation System.

The development of the Leopold matrix is described in Section 7.1. The study has identified the following major impacts:

  1. Impact of dams on soils: Dams will retain sands and silts. This will cause degradation of the downstream reach of the La Leche river, as clear water is released from the dam into the channel.

  2. Impact of dams on soil moisture: Dams will retain water. This retention will change the natural distribution of precipitation. More water will go into soil moisture, and therefore, into evapotranspiration.

  3. Impact of dams on nutrients: The reservoirs will hold sands and silts, and therefore, retain the nutrients that are embedded in the sediments. These nutrients will be sequestered and unavailable for use by plants.

  4. Impact of dams on crops: The crops inundated by the reservoir(s) will be lost. The inundated areas can be replaced by irrigated areas downstream, but the physical, chemical, and biological settings is not likely to remain the same.

  5. Impact of dams on agriculture: Substantial portions of the land, which currently are dedicated to agriculture, will be rendered inoperable by the flooding of the reservoir.

  6. Impact of dam failure on structures: Dam failure will cause catastrophic damage to structures. Therefore, the dam/reservoir should be designed using maximum security criteria (Probable Maximum Flood).

The Battelle Environmental Evaluation System is described in Section 9.2. The application of the methodology has produced a cumulative index of environmental impact EI = -26.3. The negative value indicates that the cumulative impact will be adverse. However, the small relative magnitude of EI indicates that the impact will be readily subject to mitigation.

The EES has identified the following major impacts (Tables 40 and 41):

  1. Affected fauna.

  2. Affected flora.

  3. Loss of economically useful land.

  4. Loss of swiftness of the stream.

  5. Decrease in runoff.

  6. Reduction in flood magnitude and frequency.

  7. Increase in waterbody temperature.

  8. Increase in concentration of total dissolved solids.

  9. Degradation downstream of dam.

  10. Increased ambient noise during construction.

  11. Loss of view of the river.

  12. Loss of species diversity.

  13. Loss of biodiversity.

  14. Loss of natural scenic view.

  15. Loss of fossil resources.

  16. Loss of housing.

Mitigation measures are identified. Plans are formulated to mitigate the major negative impacts that may be produced by the project.

APPENDIX

I.   The Leopold Matrix for Evaluating Environmental Impact.

II.   The Battelle Environmental Evaluation System for Water Resource Planning.

II.   The EES value functions.

REFERENCES

Dee, N., J. Baker, N. Drobny, K. Duke, and D. Fahringer. 1972. Environmental evaluation system for water resource planning (to Bureau of Reclamation, U.S. Department of Interior). Battelle Columbus Laboratory, Columbus, Ohio, January, 188 pages.

Dee, N., J. Baker, N. Drobny, K. Duke, I. Whitman, and D. Fahringer. 1973. An environmental evaluation system for water resource planning. Water Resources Research, Vol. 9, No. 3, June, 523-535.

Gobierno del Perú. 1969a. Ley General de Aguas. Decreto Ley No. 11752.

Gobierno del Perú. 1969b. Reglamento de los Títulos I, II y II de la Ley General de Aguas (Decreto Ley No. 11752), Decreto Supremo No. 261-69-AP.

Gobierno del Perú. 2001. Reglamento de Estándares Nacionales de Calidad Ambiental del Aire. Decreto Supremo No. 074-2001-PCM.

Gobierno del Perú. 2003. Reglamento de Estándares Nacionales de Calidad Ambiental para Ruido. Decreto Supremo No. 085-2003-PCM.

Leopold, L. B., F. E. Clarke, B. B. Hanshaw, and J. E. Balsley. 1971. A procedure for evaluating environmental impact. U.S. Geological Survey Circular 645, Washington, D.C.

Pardo, A., and V. Sanz. 1979. Estratigrafía del curso medio del Río La Leche, Departamento de Lambayeque. Boletín de la Sociedad Geológica del Perú, No. 60, Abril, 251-266.

Ponce, V. M., and A. V. Shetty. The facts about El Niño. (http://elnino.sdsu.edu) (090515).

Ponce, V. M., A. K. Lohani, and P. T Huston. 1997. Surface albedo and water resources: The hydroclimatological impact of human activities. Journal of Hydrologic Engineering, ASCE, Vol. 2 No. 4, October.

Ponce, V. M. 2008. La Leche River Flood Control Project: Third Project Report--Final (Hydrology), July 2, 2008. [090424].

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