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.


10.1   Endangered species

One bird species was identified as critically endangered (CE): the white-winged guan [pava aliblanca] (Penelope albipenis) (Fig 53 (a)). The habitat of this species is the relic montane ecosystem, which is not directly affected by the project.

Two bird species were identified as endangered (EN): (1) the Peruvian plantcutter [cortarrama] (Phytotoma raimondii), and (2) the rufous flycatcher [copetón rufo] (Myiarchus semirufus) (Fig 53 (b) and (c)). The habitat of these species is the floodplain ecosystem, which is not directly affected by the dam project.

(a)
(b)
(c)
Fig. 53   (a) White-winged guan (Penelope albipennis), (b) Peruvian plantcutter (Phytotoma raimondii), and
(c) rufous flycatcher (Myiarchus semirufus) (Source: Google and Wikipedia).

One tree species was identified as endangered (EN): (1) the Andean walnut [nogal andino] (Juglans neotropica). The habitat of the Andean walnut is the relic montane ecosystem, which is not directly affected by the dam project.

11.   ENVIRONMENTAL MITIGATION PLAN

The environmental mitigation plan is the crux of the environmental impact assessement. It focuses in mitigating the major negative impacts identified in the Leopold matrix and Batelle EES methods. Accordingly, a mitigation plan has been developed for the following impacts:

  • 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.

  • Increase in salinity of soil and water.

  • Loss of fossil resources.

  • Loss of natural scenic view.

  • Increase in noise during construction.

The plan consists of:

  1. Rationale

  2. Methodology

  3. Schedule

  4. Monitoring

  5. Training

  6. Human resources, and

  7. Economic resources.
The environmental mitigation plan is shown in Tables 42 (A) to 42 (L). Note that each table corresponds to each impact listed in this section.

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 (Fig. 54).
2 Methodology The ecological discharge should be developed based on local experience. In no case should it be less 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. The latter is 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 an ecological discharge. The recommended monitoring interval is once (1) per 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.

Fig. 54   La Leche river near Puchaca station [photo 080211].

Table 42 (A).   Continued.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
A2.
Recharge of groundwater downstream of dam
 		1 Rationale The aquifer downstream of 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 Groundwater baseline data, prior to reservoir operation, should be collected. A minimum of five (5) 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. 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 not 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 (5) 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 (PMF). For this purpose, the retarding-pool storage may be kept empty and ready for the PMF (Fig. 55).
3 Schedule Operational rules must be in place at all times to ensure that the emergency spillway is able to pass the PMF.
4 Monitoring Eliminating the risk of dam overtopping must have the highest priority. For this purpose, the reservoir should be monitored on a daily basis, particularly during the rainy season, and 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. 55   Storage volumes in reservoirs.

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

(1) (2) (3) (4)
Action No. Phase Mitigation plan
B1.
Degradation below dam
 		1 Rationale The water released from the dams will be relatively sediment-free, "hungry water." Thus, it will have the tendency to cause degradation downstream.
2 Methodology The phenomenon of degradation below dams has been extensively documented by Lane (1955), Ponce (2008b), and others (Fig. 56). The amount of degradation can be estimated based on principles of hydraulic engineering.

Conjunctive management of La Calzada and Calicantro reservoirs may help mitigate the effect of "hungry water," since a large portion of the water released from La Calzada may go into Calicantro, bypassing the La Leche river.

3 Schedule The degradation below dams typically occurs in the first ten (10) years of reservoir operation. Bed armoring may arrest degradation well before the new equilibrium channel slope has been established.
4 Monitoring Monitoring of channel bed degradation is recommended for at least the first five (5) years of reservoir operation. Measurements of bed profiles and associated cross sections immediately downstream of the dam should be performed every three (3) months.
5 Training The training of one (1) civil/hydraulic engineer is required to assess and monitor changes in bed profiles and associated cross sections resulting from channel degradation below the dam (La Calzada).
6 Human resources One (1) civil/hydraulic 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. 56   Degradation below Ft. Sumner Dam (Lane, 1955).

Table 42 (B).   Continued.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
B2.
Sediment accumulation in the reservoir
 		1 Rationale Sediment accumulates in the reservoir due to water storage (Fig. 57). The rate of deposition is a function of the hydraulic and sedimentological properties of the river reach. Calculations of design life, or useful life, should take into account the gradual filling of the reservoir with sediment.
2 Methodology Rate of reservoir filling of the reservoir should be estimated by appropriate methodologies. At a minimum, the Brune formula should be used to estimate design life (Ponce, 1989).
3 Schedule The rate of filling of the reservoir should be monitored every two (2) years. Bathymetric surveys are necessary to evaluate rate of filling.
4 Monitoring Monitoring of the rate of filling of the reservoir with sediment is required to follow up on the design and implement corrective measures, if necessary. Equipment for bathymetric surveys is required.
5 Training The training of one (1) civil/hydraulic engineer is required to assess and monitor rates of sediment deposition in the reservoirs (La Calzada and Calicantro).
6 Human resources One (1) civil/hydraulic 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. 57   Sediment accumulation near tail of Tinajones reservoir, Lambayeque [photo 080211].

Table 42 (C).   Mitigation plan for impact of changes in nutrient flows flow due to dam operation.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
C.
Nutrient deficiency in flood plain
 		1 Rationale Continued reservoir operation will retain sediments and cause a long-term nutrient deficiency in the downstream flood plain.
2 Methodology Nutrient deficiency can be mitigated by the proper choice of fertilizers, in addition to those commonly used.
3 Schedule A judicious use of fertilizers will be necessary to optimize the agricultural production and mitigate nutrient deficiency.
4 Monitoring Not applicable.
5 Training Not applicable.
6 Human resources Not applicable.
7 Economic resources Not applicable.


Table 42 (D).   Mitigation plan for impact of dam and reservoir construction on local fauna.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
D.
Impact on local fauna
 		1 Rationale One (1) faunal species has been identified as critically endangered (CE): the white-winged guan (Penelope albipennis). Two (2) faunal species have been identified as endangered (EN): the Peruvian plantcutter [cortarrama] (Phytotoma raimondii) and the rufous flycatcher [copetón rufo] (Myiarchus semirufus ) (Table 6, Section 5.6).
2 Methodology The habitat of the white-winged guan is the relic montane ecosystem (upstream of the dams). The habitat of the Peruvian plantcutter (Phytotoma raimondii) and the rufous flycatcher (Myiarchus semirufus ) is the floodplain ecosystem (downstream). No endangered faunal species are known to exist in the area to be flooded by La Calzada and Calicantro dams.
3 Schedule No action required.
4 Monitoring Not applicable.
5 Training Not applicable.
6 Human resources Not applicable.
7 Economic resources Not applicable.


Table 42 (E).   Mitigation plan for impact of dam and reservoir construction on local flora.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
E.
Impact on local flora
 		1 Rationale One (1) tree species has been identified as endangered (EN): the Andean walnut [nogal andino] (Juglans neotropica) (Table 7, Section 5.6).
2 Methodology The habitat on the Andean walnut (Juglans neotropica) is the relic montane ecosystem, outside of the direct influence of the dams.
3 Schedule No action required.
4 Monitoring Not applicable.
5 Training Not applicable.
6 Human resources Not applicable.
7 Economic resources Not applicable.


Table 42 (F).   Mitigation plan for loss of agricultural lands due to reservoir flooding.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
F.
Loss of agricultural lands
 		1 Rationale The flooding of La Calzada reservoir will result in the loss of valuable agricultural land. This encompasses the agricultural areas in the vicinity of Mochumi Viejo, and may reach as far upstream as La "U" and Puchaca, depending on backwater conditions.
2 Methodology The area to be inundated should be precisely determined by surveying and backwater calculations (HEC-RAS) (U.S. Army Corps of Engineers, 2002). Land values should be appraised and proper value or other compensation arranged to local landowners.
3 Schedule The survey should be carried out prior to dam construction.
4 Monitoring Not applicable.
5 Training One (1) surveyor is required to perform appropriate topographic surveys; one (1) hydraulic engineer to perform backwater calculations; one (1) rural economist to determine the value of the affected lands.
6 Human resources One (1) surveyor, one (1) hydraulic engineer, and one (1) rural economist, with field support personnel and logistical support.
7 Economic resources High (more than U.S. $50,000); nonrecurrent cost.


Table 42 (G).   Mitigation plan for loss of grazing lands due to reservoir flooding.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
G.
Loss of grazing lands
 		1 Rationale The flooding of Calicantro reservoir will result in the loss of valuable grazing land. This encompasses the "La Viña" ranch, property of Mr. Jesús Montenegro Arrascue. Mr. Montenegro raises fighting bulls [toros de lidia] on his property.
2 Methodology The area to be inundated should be precisely determined by surveying and backwater calculations (HEC-RAS) (U.S. Army Corps of Engineers, 2002). Land values should be appraised and proper value or other compensation arranged to the local landowner.
3 Schedule The survey should be carried out prior to dam construction.
4 Monitoring Not applicable.
5 Training One (1) surveyor is required to perform appropriate topographic surveys; one (1) hydraulic engineer to perform backwater calculations; one (1) rural economist to determine the value of the land.
6 Human resources One (1) surveyor, one (1) hydraulic engineer, and one (1) rural economist, with field support personnel and logistical support.
7 Economic resources High (more than U.S. $50,000); nonrecurrent cost.


Table 42 (H).   Mitigation plan for loss of housing due to reservoir flooding.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
H.
Loss of housing
 		1 Rationale The flooding of La Calzada reservoir will result in the loss of valuable housing comprised within the area to be inundated by the reservoir. This encompasses the populated areas of Mochumi Viejo and vicinity.
2 Methodology Housing values should be appraised and proper cost or compensation arranged to the local owners. Several dam height alternatives may be considered if the social costs of inundation are deemed to be excessive.
3 Schedule The survey should be carried out prior to dam construction.
4 Monitoring Not applicable.
5 Training One (1) economist or appraiser is required to determine the value of the properties.
6 Human resources One (1) economist or appraiser, with field support personnel and logistical support.
7 Economic resources High (more than U.S. $50,000); nonrecurrent cost.


Table 42 (I).   Mitigation plan for the increase in salinity of soil and water.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
I.
Increase in salinity of soil and water
 		1 Rationale The conversion or runoff to evapotranspiration results in an increase in the salinity of soils and water, as shown by the extreme example of Tulare Lake Drainage District, in California (Fig. 58). The sources of these salts have been explained by Ponce (2009a), among others.
2 Methodology A fraction of the runoff should be reserved for carrying the solids to the ocean or an appropriate sink (in this case, the La Niña Lake). The quantity of drainage waters should be a fraction of the irrigation waters. A waste runoff of 20% has been recently recommended by Ponce (2009b).
3 Schedule Baseline salt concentrations should be determined in the lands to be irrigated. The irrigated lands should be drained to eliminate and properly dispose of the salts. Drainage development should parallel irrigation development.
4 Monitoring The irrigated lands should be tested periodically to ensure that there is a measure of salt balance, i.e., no appreciable salt accumulation in the soil profile over a medium-term horizon of 10 years. Monitoring for salt balance should be performed at yearly intervals.
5 Training One (1) agricultural engineer to perform salt balance calculations. One (1) chemical engineer to perform soil and water salt concentration determinations.
6 Human resources One (1) agricultural engineer and one (1) chemical engineer or chemist, with field support personnel and logistical support.
7 Economic resources Medium (between U.S. $10,000 and U.S. $50,000); per year.


Fig. 58   Evaporation basin at Tulare Lake Drainage District, California [photo 090417].

Table 42 (J).   Mitigation plan for loss of fossil resources.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
J.
Loss of fossil resources
 		1 Rationale The lands to be flooded by La Calzada and Calicantro reservoirs are rich in paleontological resources (see Section 4.2).
2 Methodology A field survey and exploration should be conducted to determine the extent to which fossils can be found on the surface area to be flooded. Fossils found during the survey and exploration should be collected and delivered to the appropriate museums or institutions for safekeeping.
3 Schedule The paleontological survey should be carried out prior to the first filling of the reservoirs.
4 Monitoring Not applicable.
5 Training One (1) paleontologist to carry out field surveys and retrieval of fossil specimens.
6 Human resources One (1) paleontologist with field support personnel and logistical support.
7 Economic resources Low (less than U.S. $10,000); nonrecurrent cost.


Table 42 (K).   Mitigation plan for loss of natural scenic view.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
K.
Loss of natural scenic view
 		1 Rationale Once in place, the dams will create reservoirs and result in the loss of the view of the river.
2 Methodology The scenic beauty provided by the reservoir may serve to offset the loss of the scenic beauty of the stream. Architectural features such as landscaping may also help in offsetting the loss of natural scenic beauty.
3 Schedule Development plans should provide for various landscaping features to minimize the obtrusiveness of the hydraulic structures.
4 Monitoring Not applicable.
5 Training One (1) landscape architect to develop and implement plans for scenic enhancements to the project.
6 Human resources One (1) landscape architect with field support personnel and logistical support.
7 Economic resources Medium (between U.S. $10,000 and U.S. $50,000); nonrecurrent cost.


Table 42 (L).   Mitigation plan for increase in noise during construction.

(1) (2) (3) (4)
Action No. Phase Mitigation plan
L.
Increase in noise during construction
 		1 Rationale Construction operations (dam and spillway) are likely to result in increased noise levels.
2 Methodology A noise policy in agreement with the Regulation Law of National Standards for Environmental Quality for Noise (Peru) (2003) should be developed. Efforts should be made during construction to ensure that noise levels are kept under control. Extremely noisy operations should be minimized and reserved for daylight hours.
3 Schedule Increased noise levels are expected only during the construction phase (first 5 years).
4 Monitoring Monitoring to manage and control noise levels should proceed during construction phase.
5 Training One (1) mechanical engineer with field support personnel and logistical support.
6 Human resources One (1) mechanical engineer to develop and monitor noise levels during construction.
7 Economic resources Low (less than U.S. $10,000); per year, for up to five years.

12.   SUMMARY

An environmental impact assessment (EIA) study of the La Leche river flood control project is described in this report. 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 rock-fill dams, one to retain floodwaters and the other to store water for irrigation and domestic water supply. The flood-control 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 Leopold matrix is described in Section 9.1. 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 (Table 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 formulated for the major impacts identified by the Battelle methodology (Table 41).

Detailed plans are developed to mitigate the major negative impacts that may be produced by the project. The major negative impacts are grouped into similar categories and expressed as follows:

  • 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.

  • Increase in salinity of soil and water.

  • Loss of fossil resources.

  • Loss of natural scenic view.

  • Increase in noise during construction.

The most significant impacts are identified:

  • the changes in water and sediment flow (Tables 42 A and 42 B, respectively),

  • the loss of housing due to reservoir flooding (Table 42 H), and

  • the increase in salinity of soil and water (Table 42 I).
Mitigation is an established strategy to minimize the negative impacts of the flood control and water supply project.

APPENDIX

I.   The Leopold Matrix for Evaluating Environmental Impact.

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

III.   The EES value functions.

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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.

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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.

Lane, E. W. 1955. The importance of fluvial morphology in hydraulic engineering. Proceedings, American Society of Civil Engineers, Vol. 81, Paper 745, July.

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Fig. 59   Black-faced ibis [bandurria] (Theristicus melanopis ), a species rarely seen in the floodplain forests of the La Leche river.

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