Decision Analysis (DA) can be used to support practical decisions in the face of risk and uncertainty (Hubbard 2014; Howard & Abbas 2016). DA can generate robust and science-based decision support by integrating data and expert knowledge on decisions and the systems they strive to influence. We demonstrate DA model development techniques to support the difficult task of deciding which interventions to choose, if any, given a collection of possible interventions to implement. The approach embraces complexity, makes recommendations that account for the imperfect state of available knowledge and identifies critical uncertainties that decision-supporting research should address. Such decision analysis is highly applicable in data-scarce environments, such as the Upper Volta River Basin, where science has traditionally struggled to provide actionable information to policy-makers, development practitioners, NGOs and rural communities (Katic & Morris 2016).
The decisionSupport()
function is part of the package decisionSupport
(Luedeling and Göhring, 2017) in the R programming environment (R Core Team 2017). This package was used for a Monte-Carlo-based selection of a sedimentation management strategy for a reservoir in Burkina Faso. These reservoirs have multiple benefits for rural communities (Cecchi et al. 2008; Bharati et al. 2008; Venot & Cecchi 2011; Boelee et al. 2013) and are important for food security and livelihoods (Palmieri et al. 2001; Wisser et al. 2010; Poussin et al. 2015). Sedimentation is a major impediment for the functioning of these reservoirs (Kondolf et al. 2014; Schmengler 2011; Chitata et al. 2014). The design of an efficient sedimentation management intervention for the reservoir of Lagdwenda required assessment of multiple uncertain quantities and risks. The reservoir is a good prototype for testing the strategies of sedimentation management in the Volta basin. Most of the reservoirs in the Upper Volta present similar conditions and context (climatic environment, type of crops cultivated, cultural practices and the sedimentation issue) (Birner et al 2010).
A number of specialized participatory approaches and modeling techniques helped us to construct and parameterize a model based on the knowledge of local expert stakeholders. These approaches are outlined, in part, by Allan et al (2010), David et al. (2014), Fred et al (2017), Morgan (2014), Martin et al (2012) and Samantha et al (2009).
In preparation for the participatory analysis, we drafted a proposal of several intervention alternatives, based on preliminary fieldwork. These were discussed with the stakeholders in workshop plenary sessions:
An intervention that would exclude agriculture (including no deforestation or livestock grazing) on land within 100 meters of the reservoir and the immediate up-slope stream network. In this intervention the vegetation would also be restored to a mixed system (50% grass and 50% tree cover).
An intervention that would exclude agriculture and follow the same outline as the intervention described above, but with livestock grazing allowed.
An intervention that would permit selective agriculture on land within 100 meters of the reservoir and up-slope stream network. The agriculture would be designed to minimize erosion, including measures such as: no livestock grazing, no-till agricultural production with crop rotations, mulch applications, at least 50% perennial including trees, and wild grasses would be allowed to grow.
An intervention that would seek to manually dredge part of the reservoir bed and inlet river area with arbitrary disposal of sediment elsewhere.
An intervention that would seek to manually dredge part of the reservoir bed and inlet river area, as the intervention above, but with targeted disposal of sand and clay layers onto nearby farmland that lacks sand or lacks clay.
An intervention that would seek to construct small rock check dams (these are referred to as rock dams in the main text) upstream in the channel.
An intervention that would promote a type of locally preferred terracing known as fanya juu on sloping agricultural land upstream the reservoir.
An intervention that would promote bench terracing upstream of the reservoir
An intervention that would promote no-till, or minimum tillage agriculture close to riparian zones upstream of the reservoir.
An intervention that would seek to manage livestock densities in riparian areas upstream of the reservoir.
During a special workshop described in the main text, experts chose three interventions from the list above: (1) dredging along the main stream inlet; (2) building rock dams along the streams upstream; (3) implementation of a buffer protection scheme.
The third intervention proposed by the group of experts was to implement a buffer protection scheme for land around the reservoir and stream inlets. The objective of the intervention is to prevent sedimentation due to agricultural practices around the reservoir, and to reduce deposits of sediments coming from upstream.
The protection is composed of 3 buffer strips (except for land along the stream network upstream, which requires only the first buffer). The first buffer (75-100 meters) is made of stone barriers/contour bounding with stabilizing plants (grasses). The vegetation consists of grass (100% cover), delineated by stone barriers. Relevant grass species are: Andropogon gayanus, Andropogon ascinodis, Cymbopogon ascinodis, Vetiveria zizanioïdes, and Vetiveria nigritana.
The second buffer (75-100 meters; Figure 12b) consists of vegetables mixed with shrubs for firewood. The buffer consists of 20% shrub and 80 vegetables (shrubs in linear strips or scattered on the field). Possible crops are Solanum melongena (eggplant), Hibiscus sabdariffa (Roselle), Daucus carota (carrot), Brassica oleracea var capitata (cabbage), Cucumis sativus (cucumber), Cucurbita pepo (pumpkin), Fragaria ananassa (strawberry), Hibiscus esculentus (okra), Phaseolus vulgaris (common bean), Lycopersicum esculentum (tomato), Lactuca sativa (Lettuce), Manihot esculenta (Cassava), Cucumis melo (Melon), Allium cepa (onion), Citrullus vulgaris (watermelon), lpomoea batatas (sweet potato), Capsicum frutescens (chili pepper), Capsicum annuum (bell pepper), Solanum tuberosum (potato). Possible species of shrubs include: Acacia nilotica, Ziziphus mauritiana, Bauhinia rufescens, Piliostigma reticulatum, Mimosa pigra, Dichrostachys cinerea and Dichrostachys glomerata.
The third zone (75-100 meters) is a mix of crops with fruit trees. The buffer consists of 20 % fruit trees and 80% crops. Species of fruit trees include Mangifera indica (mango), Psidium guajava (guava), Citrus limon (lime), Citrus tangelo (tangerine), and Carica papaya (papaya). Regarding the crops, many common cereals such as Zea maize maize are included.
To be successful, the implementation of the buffer strips intervention should be combined with techniques to reduce surface runoff (half-moon micro-catchments, application of organic rather than synthetic fertilizers), alternative strategies to access water far from the reservoir (dug wells), education action (e.g. signs to be put up around the area to raise awareness of sediment management activities) and delineation of livestock access routes to the reservoir (exact location and number of these needs to be agreed with a local experts).
By coding a participatory conceptual model as a Monte Carlo simulation using the decisionSupport()
function in the R package decisionSupport
we were able to offer decision makers probable outcomes in terms of Net Present Value (NPV) and cash flow for the intervention decisions (including combined interventions) and to identify variables that most affected the overall outcome of the different decisions.
The input table Sediment_input_table.csv
contains the variables used in the model with distributions described by a 90% confidence interval, as well as the shape of the distribution.
Description | label | variable | distribution | lower | median | upper |
---|---|---|---|---|---|---|
GENERAL | ||||||
Years from the start of the implementation of the intervention to the end. | Project time horizon | n_years | const | 30.00 | 30.00 | |
Coefficient of variation, ratio of the standard deviation to the mean (a measure of relative variability). | coeff. Variation | var_CV | posnorm | 5.00 | 20.00 | |
Percentage discounting as a measurement of time preference for benefits and costs. | discount rate | discount_rate | posnorm | 1.00 | 5.00 | |
GENERAL RISKS | ||||||
Percentage risk that a natural hazard may occur. | Risk of natural hazard | NaturHazard | tnorm_0_1 | 0.10 | 0.30 | |
Percentage risk that a chosen intervention will be poorly managed. | Risk of bad maintenance | BadMaintenance | tnorm_0_1 | 0.20 | 0.50 | |
Percentage risk that a chosen intervention will be poorly designed. | Risk of bad design | BadDesign | tnorm_0_1 | 0.20 | 0.50 | |
Percentage risk that the communities surrounding the reservoir will not comply with requirements for intervention effectiveness. | Risk of non compliance | NonCompliance | tnorm_0_1 | 0.20 | 0.50 | |
Percentage risk that the communities surrounding the reservoir will not help with the implementation of the dredging intervention. | Risk pop non involv (dredg.) | dredge_NonPopInvolv | tnorm_0_1 | 0.05 | 0.15 | |
Percentage risk that the necessary donors (local and national governments, local NGOs) will not help with the implementation of the dredging intervention. | Risk donors non involv (dredg.) | dredge_NonDonorsInvolv | tnorm_0_1 | 0.04 | 0.10 | |
Percentage risk that the communities surrounding the reservoir will not help with the implementation of the check dam intervention. | Risk pop non involv (check d.) | check_NonPopInvolv | tnorm_0_1 | 0.05 | 0.15 | |
Percentage risk that the necessary institutions (local and national governments, local NGOs) will not help with the implementation of the check dam intervention. | Risk instit. non involv (check d.) | check_NonInstInvolv | tnorm_0_1 | 0.02 | 0.10 | |
Percentage risk that the necessary donors (local and national governments, local NGOs) will not help with the implementation of the check dam intervention. | Risk donors non involv (check d.) | check_NonDonorsInvolv | tnorm_0_1 | 0.04 | 0.10 | |
Percentage risk that the communities surrounding the reservoir will not help with the implementation of the buffer strip intervention. | Risk pop non involv (buffer s.) | buffer_NonPopInvolv | tnorm_0_1 | 0.10 | 0.30 | |
Percentage risk that the necessary institutions (local and national governments, local NGOs) will not help with the of the buffer strip intervention. | Risk instit. non involv (buffer s.) | buffer_NonInstInvolv | tnorm_0_1 | 0.05 | 0.15 | |
Percentage risk that the necessary donors (local and national governments, local NGOs) will not help with the implementation of the buffer strip intervention. | Risk donors non involv (buffer s.) | buffer_NonDonorsInvolv | tnorm_0_1 | 0.04 | 0.10 | |
IRRGATION AREA | ||||||
The total current area (ha) of irigation downstream formal irrigation area (scheme 1) | current irrigated area D/S | current_irrig_area | posnorm | 9.00 | 10.00 | |
LIVESTOCK | ||||||
Tropical Livestock Units that are kept in the reservoir area and, at least partly, dependent on reservoir water | TLU (baseline) | TLU_no_buffer | posnorm | 8700.00 | 13000.00 | |
Percentage change (reduction or growth of population) in Tropical Livestock Units that are kept in the reservoir area if the buffer strips are implemented | TLU change if buffer s. | change_TLU_buffer_perc | norm | -0.10 | 0.10 | |
Livestock keepers profit (USD) per Tropical Livestock Unit. | profit per TLU | profit_per_TLU | posnorm | 40.00 | 120.00 | |
IRRIGATION AREA | ||||||
The total area (ha) of irigation downstream formal irrigation area (scheme 1) that would be lost if the pipes that provide water from the reservoir were clogged. | Irrigated area D/S lost if pipes clogged | pipe_blocked_area_lost_perc | posnorm | 10.00 | 50.00 | |
DREDGING COSTS | ||||||
The costs (USD) of a necessary study to plan the dredging intervention. | Study cost (dredg.) | dredging_study_cost | posnorm | 7200.00 | 8000.00 | |
The costs (USD) of necessary supervision to implement the dredging intervention. | Supervision costs (dredg.) | dredging_supervision_cost | posnorm | 1600.00 | 4800.00 | |
The costs (USD) of necessary administrative costs for implementing the dredging intervention. | Admin. costs (dredg.) | dredging_admin_cost | posnorm | 720.00 | 880.00 | |
The costs (USD) of necessary transportation when implementing the dredging intervention. | Transport costs (dredg.) | dredging_transport_cost | posnorm | 1450.00 | 1930.00 | |
The costs (USD) of necessary communications (phones etc.) when implementing the dredging intervention. | Communication costs (dredg.) | dredging_communication_cost | posnorm | 720.00 | 880.00 | |
The costs (USD) of a feasibility assessment for building culverts as part of the dredging intervention. | Culvert-feasibility costs (dredg.) | dredging_culvert_feasibility_cost | posnorm | 1300.00 | 1600.00 | |
The costs (USD) of necessary supervision for culvert construction when implementing the dredging intervention. | Culvert-supervision costs (dredg.) | dredging_culvert_supervision_cost | posnorm | 640.00 | 800.00 | |
CHECK DAM COSTS | ||||||
The costs (USD) of a feasibility assessment for building culverts as part of the check dam intervention. | Localization cost (check d.) | check_location_cost | posnorm | 1600.00 | 4800.00 | |
The costs (USD) of a feasibility assessment for the check dam intervention. | Feasibility cost (check d.) | check_feasibility_cost | posnorm | 9600.00 | 14500.00 | |
The costs (USD) of topobathymetry mapping and assessment for the check dam intervention. | Topobathymetry cost (check d.) | check_topobatymetry_cost | posnorm | 1000.00 | 1600.00 | |
The costs (USD) of necessary supervision to implement the check dam intervention. | Supervision cost (check d.) | check_supervision_cost | posnorm | 960.00 | 3200.00 | |
The costs (USD) of training workers to implement the check dam intervention. | Training cost (check d.) | check_training_cost | posnorm | 960.00 | 3200.00 | |
The costs (USD) of necessary communications (phones etc.) when implementing the check dam intervention. | Communication cost (check d.) | check_communication_cost | posnorm | 1600.00 | 4800.00 | |
The costs (USD) of necessary technical devices (gps etc.) when implementing the check dam intervention. | Cost tech devices (check d.) | check_tech_devices_cost | posnorm | 640.00 | 1300.00 | |
The costs (USD) of necessary materials (wire, posts etc.) when implementing the check dam intervention. | Material cost (check d.) | check_material_cost | posnorm | 5600.00 | 10500.00 | |
The costs (USD) of rocks when implementing the check dam intervention. | Cost of rocks (check d.) | check_rocks_cost | posnorm | 4800.00 | 8000.00 | |
The costs (USD) of transportation when implementing the check dam intervention. | Transport costs (check d.) | check_transport_cost | posnorm | 3200.00 | 6400.00 | |
BUFFER STRIP COSTS | ||||||
The costs (USD) of necessary communications (phones etc.) when implementing the buffer strip intervention. | Communication cost (buffer s.) | buffer_communication_cost | posnorm | 5000.00 | 20000.00 | |
The costs (USD) of zoning areas when implementing the buffer strip intervention. | Zoning cost (buffer s.) | buffer_zoning_cost | posnorm | 3000.00 | 29000.00 | |
The costs (USD) of planting materials and labor when implementing the buffer strip intervention. | Plantation cost (buffer s.) | buffer_adaptation_cost | posnorm | 20000.00 | 130000.00 | |
The costs (USD) of necessary technical devices when implementing the buffer strip intervention. | Cost tech devices (buffer s.) | buffer_tech_devices_cost | posnorm | 1000.00 | 4800.00 | |
The costs (USD) of building and maintaining a tree and shrub nursery when implementing the buffer strip intervention. | Cost of the nursery (buffer s.) | buffer_nursery_cost | posnorm | 2000.00 | 18000.00 | |
The costs (USD) of digging wells when implementing the buffer strip intervention. | Cost of digging wells (buffer s.) | buffer_wells_cost | posnorm | 20000.00 | 80000.00 | |
The costs (USD) of training workers to implement the buffer strip intervention. | Training cost (buffer s.) | buffer_training_cost | posnorm | 8000.00 | 46000.00 | |
The costs (USD) of necessary equipment (shovels, hoes etc.) when implementing the buffer strip intervention. | Equipment cost (buffer s.) | buffer_mngmt_oprt_cost | const | 0.00 | 0.00 | |
The costs (USD) of follow up work and monitoring of the buffer strip intervention. | Monitoring cost (buffer s.) | buffer_mngmt_follow_cost | const | 0.00 | 0.00 | |
The costs (USD) of an audit of the buffer strip intervention. | Audit cost (buffer s.) | buffer_mngmt_audit_cost | const | 0.00 | 0.00 | |
DOWNSTREAM LOSSES | ||||||
The percentage of the area of the downstream formal irrigation area (scheme 1) that would be lost in the case of a natural hazard. | Irrigated area D/S lost if hazard | Hazard_reduction_irrigated_area | posnorm | 10.00 | 30.00 | |
The percentage of the area of the downstream formal irrigation area (scheme 1) that would be lost in the case of bad maintenance of an intervention. | Irrigated area D/S lost if bad maint. | BadMaint_reduction_irrigated_area | posnorm | 10.00 | 30.00 | |
The percentage of the area of the downstream formal irrigation area (scheme 1) that would be lost in the case of a bad design of an intervention. | Irrigated area D/S lost if bad design | BadDesign_reduction_irrigated_area | posnorm | 10.00 | 30.00 | |
MAINTENANCE COSTS | ||||||
The costs (USD) of maintaining the check dam intervention. | maintenance cost (check d.) | maintenance_check_dams | posnorm | 160.00 | 400.00 | |
The costs (USD) of maintaining the buffer strip intervention. | maintenance cost (buffer s.) | maintenance_buffer_strips | posnorm | 800.00 | 7000.00 | |
UPSTREAM IRRIGATION AREA | ||||||
The current area (ha) of the upstream informal cropping area (scheme 2). | current irrigated area U/S | scheme2_area_no_dredging_ha | posnorm | 0.50 | 3.00 | |
The percentage increase in area of the upstream informal cropping area (scheme 2) if the dredging intervention is implemented. | increase in irrigated area U/S if dredg. | dredging_bump_scheme2_area_perc | posnorm | 10.00 | 30.00 | |
Number of years that the dredging intervention would delay the reduction in area of the upstream informal cropping area (scheme 2). | Delay in irrigated area decline U/S (dredg.) | scheme2_time_until_dredging_benefits_gone_baseline | posnorm | 2.00 | 4.00 | |
Number of years that the check dam intervention would delay the reduction in area of the upstream informal cropping area (scheme 2). | Delay in irrigated area decline U/S (check d.) | check_dams_added_scheme2_area_benefit_time | posnorm | 2.00 | 4.00 | |
Vegetable yields (ton per ha) in the upstream informal cropping area (scheme 2). | Yields per ha-vegetable U/S | scheme2_vegetable_yield_t_ha | posnorm | 5.00 | 10.00 | |
Profits (USD per ton) from vegetables grown in the upstream informal cropping area (scheme 2). | Profit per ton-vegetable U/S | scheme2_vegetable_profit_USD_t | posnorm | 50.00 | 150.00 | |
Yields (ton per ha) in the upstream informal cropping area (scheme 2). | Yields per ha-rice U/S | scheme2_rice_yield_t_ha | posnorm | 1.50 | 2.00 | |
Profits (USD per ton) from rice grown in the upstream informal cropping area (scheme 2). | Profit per ton-rice U/S | scheme2_rice_profit_USD_t | norm | 100.00 | 500.00 | |
BUFFER STRIP CROPS | ||||||
Area (ha) where vegetables would be grown in the buffer strip. | Vegetable area in ha (buffer s.) | buffer_vegetable_area_ha | posnorm | 5.00 | 7.00 | |
Area (ha) where fruits would be grown in the buffer strip. | Fruit area in ha (buffer s.) | buffer_fruit_area_ha | posnorm | 1.00 | 2.00 | |
Area (ha) where rainfed crops would be grown in the buffer strip. | Rainfed crop area in ha (buffer s.) | buffer_rainfed_crop_area_ha | posnorm | 6.00 | 8.00 | |
Vegetable yields (ton per ha) in the buffer strip. | Yields per ha-vegetable (buffer s.) | buffer_vegetable_yield_t_ha | posnorm | 5.00 | 10.00 | |
Fruit yields (ton per ha) in the buffer strip. | Yields per ha-fruit (buffer s.) | buffer_fruit_yield_t_ha | posnorm | 10.00 | 30.00 | |
Yields (ton per ha) of rainfed crops in the buffer strip. | Yields per ha-rainfed crops (buffer s.) | buffer_rainfed_crop_yield_t_ha | posnorm | 1.00 | 3.00 | |
Profits (USD per ton) from vegetables grown in the buffer strip. | Profit per ton-vegetable (buffer s.) | buffer_vegetable_profit_USD_t | posnorm | 100.00 | 200.00 | |
Profits (USD per ton) from fruits grown in the buffer strip. | Profit per ton-fruit (buffer s.) | buffer_fruit_profit_USD_t | posnorm | 100.00 | 200.00 | |
Profits (USD per ton) from rainfed crops grown in the buffer strip. | Profit per ton-rainfed crops (buffer s.) | buffer_rainfed_crop_profit_USD_t | posnorm | 50.00 | 200.00 | |
DOWNSTREAM CROPS | ||||||
The percentage of the area of the downstream formal irrigation area (scheme 1) planted with rice. | Rice area’s share D/S in rainy season | proportion_irrigation_scheme_rice | tnorm_0_1 | 0.30 | 0.60 | |
Yields (ton per ha) of rice in the downstream formal irrigation area (scheme 1) | Yields per ha-rice D/S | irrigation_scheme_rice_yield_t_ha | posnorm | 1.50 | 2.50 | |
Profits (USD per ton) of rice in the downstream formal irrigation area (scheme 1) | Profit per ton-rice D/S | irrigation_scheme_rice_profit_USD_t | posnorm | 100.00 | 500.00 | |
Yields (ton per ha) of vegetables in the downstream formal irrigation area (scheme 1) | Yields per ha-vegetable D/S | irrigation_scheme_vegetable_yield_t_ha | posnorm | 8.00 | 15.00 | |
Profits (USD per ton) of vegetables in the downstream formal irrigation area (scheme 1) | Profit per ton-vegetable D/S | irrigation_scheme_vegetable_profit_USD_t | posnorm | 100.00 | 300.00 | |
RESERVOIR IRRIGATION PIPES | ||||||
Baseline percentage risk that irrigation pipes from the reservoir are blocked with sediment. | Risk of pipe blockage (at present) | current_risk_of_pipe_blockage | tnorm_0_1 | 0.20 | 0.40 | |
Baseline time (years) before irrigation pipes from the reservoir are blocked with sediment every second year. | Years bef. blockage every 2nd year (basel.) | baseline_time_until_pipes_blocked_every_second_year | posnorm | 3.00 | 5.00 | |
Number of years that the dredging intervention would delay irrigation pipes from the reservoir being blocked with sediment every second year. | Delay in blockage every 2nd year (dredg.) | dredging_delay_of_pipes_blocked_every_second_year | posnorm | 1.00 | 3.00 | |
Number of years that the check dam intervention would delay irrigation pipes from the reservoir being blocked with sediment every second year. | Delay in blockage every 2nd year (check d.) | check_dam_delay_of_pipes_blocked_every_second_year | posnorm | 2.00 | 4.00 | |
Number of years that the buffer strip intervention would delay irrigation pipes from the reservoir being blocked with sediment every second year. | Delay in blockage every 2nd year (buffer s.) | buffer_strip_delay_of_pipes_blocked_every_second_year | posnorm | 4.00 | 7.00 | |
Baseline percentage chance that irrigation pipes from the reservoir are cleared when blocked with sediment. | Chance of blocked pipe cleared (at present) | current_chance_of_blocked_pipe_cleared | tnorm_0_1 | 0.70 | 0.90 | |
Years until the chance of clearing irrigation pipes is half of the baseline rate. | Years bef. P(blockage cleared)=0.5 (basel.) | baseline_time_until_chance_cleared_50percent | posnorm | 7.00 | 10.00 | |
Years until the chance of clearing irrigation pipes is half of the baseline rate. | Delay bef. P(blockage cleared)=0.5 (dredg.) | dredging_delay_of_time_until_chance_cleared_50percent | posnorm | 1.00 | 2.00 | |
Years until the chance of clearing irrigation pipes is half of the baseline rate if the check dam intervention is implemented. | Delay bef. P(blockage cleared)=0.5 (check d.) | check_dam_delay_of_time_until_chance_cleared_50percent | posnorm | 2.00 | 4.00 | |
Years until the chance of clearing irrigation pipes is half of the baseline rate if the buffer strip intervention is implemented. | Delay bef. P(blockage cleared)=0.5 (buffer s.) | buffer_strip_delay_of_time_until_chance_cleared_50percent | posnorm | 4.00 | 6.00 | |
DECLINE DOWNSTREAM | ||||||
Baseline time (years) until the irrigable area in the downstream formal irrigation area (scheme 1) begins to decline. | Years bef. decline irrigable area D/S (basel.) | baseline_time_until_irrig_area_declines | posnorm | 1.00 | 4.00 | |
Number of years that the dredging intervention would delay the reduction in area of the downstream formal irrigation area (scheme 1). | Delay in irrigable area decline D/S (dredg.) | dredging_delay_of_irrig_area_decline | posnorm | 2.00 | 5.00 | |
Number of years that the check dam intervention would delay the reduction in area of the downstream formal irrigation area (scheme 1). | Delay in irrigable area decline D/S (check d.) | check_dam_delay_of_irrig_area_decline | posnorm | 4.00 | 7.00 | |
Number of years that the buffer strip intervention would delay the reduction in area of the downstream formal irrigation area (scheme 1). | Delay in irrigable area decline D/S (buffer s.) | buffer_strip_delay_of_irrig_area_decline | posnorm | 4.00 | 15.00 | |
Baseline time (years) until the irrigable area in the downstream formal irrigation area (scheme 1) is half of the current area. | Years bef. irrigable area halved D/S (basel.) | baseline_start_losses_to_half_irrig_area_lost | posnorm | 8.00 | 15.00 | |
Number of years that the dredging intervention would delay the reduction in area of the downstream formal irrigation area (scheme 1) to half of the current size. | Delay in irrigable area halved D/S (dredg.) | dredging_delay_of_irrig_area_halved | posnorm | 1.00 | 2.00 | |
Number of years that the check dam intervention would delay the reduction in area of the downstream formal irrigation area (scheme 1) to half of the current size. | Delay in irrigable area halved D/S (check d.) | check_dam_delay_of_irrig_area_halved | posnorm | 3.00 | 5.00 | |
Number of years that the buffer strip intervention would delay the reduction in area of the downstream formal irrigation area (scheme 1) to half of the current size. | Delay in irrigable area halved D/S (buffer s.) | buffer_strip_delay_of_irrig_area_halved | posnorm | 8.00 | 20.00 | |
DECLINE UPSTREAM | ||||||
Baseline time (years) until the irrigable area in the upstream informal cropping area (scheme 2) begins to decline. | Years bef. decline irrigable area U/S (basel.) | baseline_time_until_irrig_area2_declines | posnorm | 3.00 | 6.00 | |
Number of years that the dredging intervention would delay the reduction in area of the upstream informal cropping area (scheme 2). | Delay in irrigable area decline U/S (dredg.) | dredging_delay_of_irrig_area2_decline | posnorm | 3.00 | 5.00 | |
Number of years that the check dam intervention would delay the reduction in area of the upstream informal cropping area (scheme 2). | Delay in irrigable area decline U/S (check d.) | check_dam_delay_of_irrig_area2_decline | posnorm | 2.00 | 6.00 | |
Baseline time (years) until the irrigable area in the upstream informal cropping area (scheme 2) is half of the current area. | Years bef. irrigable area halved U/S (basel.) | baseline_start_losses_to_half_irrig_area2_lost | posnorm | 10.00 | 17.00 | |
Number of years that the dredging intervention would delay the reduction in area of the upstream informal cropping area (scheme 2) to half of the current size. | Delay in irrigable area halved U/S (dredg.) | dredging_delay_of_irrig_area2_halved | posnorm | 1.00 | 2.00 | |
Number of years that the check dam intervention would delay the reduction in area of the upstream informal cropping area (scheme 2) to half of the current size. | Delay in irrigable area halved U/S (check d.) | check_dam_delay_of_irrig_area2_halved | posnorm | 3.00 | 5.00 | |
FISH | ||||||
The baseline annual value (USD) of fish in the reservoir. | Annual fish value (baseline) | current_annual_fish_value_USD | posnorm | 500.00 | 2000.00 | |
The percentage of fish in the reservoir that would be lost in the case of a natural hazard. | Fish reduction if hazard | Hazard_reduction_fish_perc | posnorm | 5.00 | 15.00 | |
Baseline time (years) until the current fish population in the reservoir begins to decline. | Years bef. decline in fish (basel.) | time_to_start_fish_decline_baseline | posnorm | 1.00 | 3.00 | |
Number of years that the dredging intervention would delay the reduction in the fish population in the reservoir. | Delay in fish decline (dredg.) | dredging_delay_start_fish_decline | posnorm | 1.00 | 2.00 | |
Number of years that the check dam intervention would delay the reduction in the fish population in the reservoir. | Delay in fish decline (check d.) | check_dams_delay_start_fish_decline | posnorm | 2.00 | 4.00 | |
Number of years that the buffer strip intervention would delay the reduction in the fish population in the reservoir. | Delay in fish decline (buffer s.) | buffer_strips_delay_start_fish_decline | posnorm | 3.00 | 6.00 | |
Baseline time (years) until the fish population in the reservoir is half of the current size. | Years bef. fish pop. halved D/S (basel.) | time_to_halve_fish_population_baseline | posnorm | 14.00 | 20.00 | |
Number of years that the dredging intervention would delay the reduction of the fish population to half of the current size. | Delay in fish pop. halved (dredg.) | dredging_delay_in_time_to_halve_fish_population | posnorm | 1.00 | 2.00 | |
Number of years that the check dam intervention would delay the reduction of the fish population to half of the current size. | Delay in fish pop. halved (check d.) | check_dams_delay_in_time_to_halve_fish_population | posnorm | 2.00 | 4.00 | |
Number of years that the buffer strip intervention would delay the reduction of the fish population to half of the current size. | Delay in fish pop. halved (buffer s.) | buffer_strips_delay_in_time_to_halve_fish_population | posnorm | 5.00 | 8.00 |
To set up the analysis we first define the variable n_years
to indicate the 30 year timeline for assessing the impacts of the intervention decision.
We define the probabilities of four ex-post risks (natural hazards, bad maintenance, and bad design) as possible impacts on the benefits probability, and three ex-ante risks (non-involvement of the local population, the institutions, and the donors) as possible impacts on the implementation of interventions.
Certain events can either occur or not, and values for dependent variables can depend on which of the cases occurs. The chance_event()
function randomly simulates whether events occur and returns output values accordingly. The outputs can be single values or a series of values, with the option of introducing artificial variation into this dataset.
The identified ex-post and ex-ante risks were all assigned probability ranges from 0 to 1 and the chance_event()
function was used to simulate a time series of their occurrence. The following lines of R code produce a series for the chance of the identified ex-ante or ex-post risk occurrences over 30 years (n_years
). It simulates a random chance of the occurrence (value_if = 1) or not (value_if_not = 0) of the event.
We used the chance_event()
function for simulation of ex-ante risks as impacts on the implementation of the three interventions.
Probability distributions for the chance variables dredge_NonPopInvolv
, dredge_NonDonorsInvolv
are defined in the input table Sediment_input_table.csv
.
dredge_NonPopInvolvEvent<-chance_event(dredge_NonPopInvolv,value_if = 1,value_if_not =0,n=1)
dredge_NonDonorsInvolvEvent<-chance_event(dredge_NonDonorsInvolv,1,value_if_not =0,n=1)
The ex-ante risk of lack of donor involvement was not considered valid for the dredging. This is because the main investment for the dredging intervention would be labor that, in principle, would be donated by the local communities.
check_NonPopInvolvEvent<-chance_event(check_NonPopInvolv,value_if = 1,value_if_not =0,n=1)
check_NonInstInvolvEvent<-chance_event(check_NonInstInvolv,value_if = 1,value_if_not =0,n=1)
check_NonDonorsInvolvEvent<-chance_event(check_NonDonorsInvolv,value_if = 1,value_if_not = 0,n=1)
buffer_NonPopInvolvEvent<-chance_event(buffer_NonPopInvolv,value_if = 1,value_if_not =0,n=1)
buffer_NonInstInvolvEvent<-chance_event(buffer_NonInstInvolv,value_if = 1,value_if_not = 0,n=1)
buffer_NonDonorsInvolvEvent<-chance_event(buffer_NonDonorsInvolv,value_if = 1,value_if_not = 0,n=1)
We used the chance_event()
function for simulation of the four ex-post risks as impacts on the benefits. Probability distributions for the chance variables NaturHazard
, BadMaintenance
and BadDesign
included in the code below, are all defined in the input table Sediment_input_table.csv
.
HazardEvent<-chance_event(NaturHazard,value_if = 1,value_if_not =0,n=n_years)
BadMaintEvent<-chance_event(BadMaintenance,value_if = 1,value_if_not =0,n=n_years)
In the case of the ex-post risk of design problems (BadDesign
) of the reservoir we used the option one_draw
within the chance_event()
function. one_draw
is a boolean coefficient. By indicating that one_draw=TRUE
the event occurrence BadDesign
is determined only once with results applying to all elements of the results vector BadDesignEvent
.
BadDesignEvent<-chance_event(BadDesign,value_if = 1,value_if_not =0,n=n_years, one_draw = TRUE)
Many of the variables included in the model were considered to vary considerably over time and we chose to include this variation in the time series analyses. To do this we used the value varier function vv()
to produce a time series that contains variation from a specified mean and coefficient of variation.
The probability distributions for the mean of the variable to be varied (the first argument in the vv()
function) and the coefficient of variation (var_CV
) are listed among the variables in Sediment_input_table.csv
. var_CV
is assigned an upper and lower bound (5% and 20%).
The value varier function vv()
was applied to the identified ex-ante risks on the irrigation area.
Hazard_scaling_irrig_area<-1-HazardEvent*vv(Hazard_reduction_irrigated_area,var_CV,n=n_years)/100
BadMaint_scaling_irrig_area<-1-BadMaintEvent*vv(BadMaint_reduction_irrigated_area,var_CV,n=n_years)/100
BadDesign_scaling_irrig_area<-1-BadDesignEvent*vv(BadDesign_reduction_irrigated_area,var_CV,n=n_years)/100
We also used vv()
for simulation of common random draws for all intervention model runs.
Livestock were calculated as Tropical Livestock Units (TLU), with the exclusion of the possibility of TLU inside the buffer zone if the buffer zone intervention was implemented. We used the vv()
function to simulate expected variation in TLU and profits from TLU.
TLU<-vv(TLU_no_buffer,var_CV,n_years)
TLU_profit<-vv(profit_per_TLU,var_CV,n_years)
Crops were grown in two different areas, one formal irrigation scheme downstream of the dam and one informal cropping area upstream of the dam.