*2.1. Participatory Modelling*

The technical complexity and scale of the Ganga Basin makes its rejuvenation a problem in which there is a need both for enhanced system understanding and for balancing of a diversity of stakeholder values and perspectives. A participatory modelling approach [8] was applied to facilitate a robust technical analysis to increase existing knowledge on the Ganges River system. Direct interaction with stakeholders facilitated the input of important local knowledge, open discussion of results, interventions, scenarios and strategies. This is the first time a participatory modelling approach has been applied for the Ganga Basin in India.

Participatory modeling refers in this case to the integration of four distinct approaches that can be applied to support strategic basin planning: (i) water resources planning, e.g., the assessment of the impact of different planning alternatives; (ii) the use of scientific knowledge by means of computer-based models to assess impacts; (iii) stakeholder participation in the definition of objectives, indicators, models, interventions, scenarios and strategies; and (iv) collaboration, in the sense of negotiation between stakeholders to reach a decision on the desired plan (Figure 2) [8].

**Figure 2.** Collaborative modeling for policy analysis.

For system and model definition we adapted and applied a Group Model Building (GMB) approach, a participatory technique to explore constructively and synthesize themultitude of stakeholder perceptions of the interactions in the river system [9,10]. GMB was used particularly for problem and indicator identification and scenario definition, and its results informed the development and application of the computational framework. Further stakeholder engagement was carried out for model validation and strategy development in working groups and workshop settings, where a combination of plenary and focus group discussion techniques were applied.

To effectively involve the range of key technical partners and other stakeholders (both hereafter collectively referred to as 'stakeholders') in the entire Ganga Basin in India, we distinguished different geographical levels (basin and state), and different involvement levels (circles of influence).

2.1.1. Determining Stakeholder Involvement: 'Circles of Influence'

We used a circles of influence approach [11] to structure the participatory planning process for the Strategic Basin Planning in the Ganges River Basin. This approach has been successfully applied in many programs and projects worldwide.

The circles of influence approach engages different stakeholders in various formats and levels of intensity. The generic Circles of Influence framework includes four circles: Circle A—Model Developers, Circle B—Model Users and Validators, Circle C—Interested Parties, and Circle D—Decision Makers (Figure 3). In this project, Circle A stakeholders comprised governmental agencies, such as CWC (Central Water Commission) and CGWB (Central Ground Water Board), and knowledge institutes, such as NIH (National Institute of Hydrology). They were responsible for co-developing the model together with the international technical team. They were trained in hydrologic and river system modelling and were involved in training and capacity building of stakeholders in other circles. Several working groups were organized with Circle B stakeholders—the model validators and users. Circle C stakeholders were consulted at several moments throughout the planning process through multiple consultation meetings conducted in each of the riparian states. Decision makers (Circle D) were also periodically informed and consulted. Stakeholder identification and analysis was conducted during project inception to map stakeholders to their respective circles of influence [11].

**Figure 3.** The "circles of influence" process framework [11].

#### 2.1.2. Implementation of the Participation Process

The different stakeholder groups were each engaged in different ways at different stages of the development of the decision-support system (Table 1). The dashboard mentioned in the table is a visualization tool developed to analyze and compare model results (see Section 2.2.6 for details).



In the basin-wide workshops, representatives from national organizations as well as from the eleven States participated. In the different state workshops, participation was limited mostly to representatives from organizations from the hosting state. The first basin-wide workshop (January 2016) and the first series of state meetings in all eleven Ganga Basin States (February–May 2016) were used to introduce project assignments to state-level stakeholders and seek stakeholder responses on the project assignment and circulate stakeholder questionnaires to assess concerns and ideas on water management in the Ganga Basin. The second basin-wide workshop (July 2016) and the second series of state meetings (July–November 2016) were used to validate and further elaborate the findings from the questionnaires for input into the technical modeling process. On average, 25 participants from 10–15 organizations participated in each of the state workshops.

The results of the second series of consultations was used to improve the Ganga River Basin Model and the dashboard developed to present its results. The third basin-wide workshop (March 2017) and the third series of state meetings (March–June 2017) focused on the validation of the model results for the present situation and for the development of scenarios and strategies.

#### *2.2. Computational Framework*

A model to support strategic planning should include all essential components of the system and their interactions in order to be able to assess the impact of scenarios and strategies. However, the amount of detail that can be included in the model is limited. The value of the model is in its schematic representation of reality. Previous modelling exercises for the Ganga Basin include:


All three reports mention issues regarding lack of data for model input as well as calibration, and all three show calibration results with varying degrees of acceptability, as well as results from limited scenario analysis. Ref. [12,13] are limited to surface water hydrology. Ref. [14] combines modeling of surface and groundwater, but the interaction between the two systems is not modelled dynamically. Only [12] includes water quality modeling, but no calibration is included. None of these modelling exercises includes impacts on ecology and the results. The recommendations of these studies have had little impact on management and planning for the Ganga Basin [15]. Model input and output generated as part of these three studies have not been made available publicly and can therefore not be used as a starting point for new modeling.

The Ganga River Basin Model presented in this paper has a very wide scope allowing for an integrated assessment of impacts related to hydrology, geohydrology, water resources management, water quality and ecology. This is the first time that all these aspects have been integrated into one modelling approach. The level of detail included is limited to keep the model manageable and the complexity understandable.

The model components and their interactions (Figure 4) are described in the remainder of this Section, focusing on the input data and the interaction between the model components with references provided for detailed descriptions of the individual components.

**Figure 4.** Schematic representation of the workflow of the different model components of the Ganga River Basin Model.

The hydrological models cover the entire Ganga Basin upstream of Farakka Barrage including those parts of the upstream basin located in Nepal and China. This permits robust assessment of the upstream flows. On request of the state of West Bengal, the part of the catchment west of the Hooghly branch below Farakka was also been included in the model area. The remainder of the analysis focuses on the Indian part of the basin upstream of Farakka Barrage.
