Understand the PDG

What the PDG is, how it came about, how it underpins the PNPCA, and how training support its use.

Mekong River landscape illustrating the PDG journey

What is the PDG?

The Preliminary Design Guidance for Proposed Mainstream Dams in the Lower Mekong River Basin (PDG) is one of the MRC’s most important technical instruments. It sets out performance targets and design principles to avoid, minimise and mitigate the environmental, social and safety risks of proposed mainstream hydropower dams. The PDG focuses on regional and transboundary issues.

Purpose

The PDG gives developers, Member Countries and their consultants a common technical reference for the design and operation of mainstream dams and gives the MRC a consistent basis for reviewing project proposals. It is intended to be used early — during project preparation — so that risks are designed out rather than mitigated after the fact. The PDG also applies to the operational phase, post construction.

What the PDG is, and is not

  • It is guidance. The PDG provides performance targets and good-practice design and operating principles. It is not a binding regulation and does not, in itself, approve or reject a project. It does not replace national laws and regulations. It focused on transboundary issues and does not cover environmental and social issues confined within a nation’s borders, for example resettlement.
  • It underpins the PNPCA. The PDG provides the technical benchmarks used when a proposed mainstream dam is reviewed through the Procedures for Notification, Prior Consultation and Agreement (PNPCA).
  • It is basin-wide. It reflects the shared interests of Cambodia, Lao PDR, Thailand and Viet Nam in a healthy, productive and safe Mekong mainstream.

How it is structured

The PDG 2022 is organised into eight technical topics: hydrology and hydraulics; sediment transport and geomorphology; water quality; aquatic ecology; fish and fisheries; dam safety; navigation; and riparian communities and river-based livelihoods. Each topic sets objectives, performance targets and design or operating principles.

How the PDG developed

The PDG has evolved with the basin. First issued in 2009, it was comprehensively updated through a five-year process involving all four Member Countries, culminating in endorsement by the MRC Joint Committee and Council in September 2022 and publication in February 2023. The timeline below marks the key milestones.

  1. 2003
    PNPCA adopted. The Procedures for Notification, Prior Consultation and Agreement come into force — the process the PDG would later support.
  2. 2009
    First PDG issued. The original Preliminary Design Guidance for proposed mainstream dams is published, covering hydrology, sediment, water quality, fisheries, navigation and dam safety.
  3. 2010–2011
    First application. The PDG 2009 is applied in the Xayaburi Prior Consultation — the first mainstream PNPCA case.
  4. 2018
    Evidence base. The MRC Council Study and related assessments deepen the science underpinning a PDG update.
  5. 2018–2022
    Five-year update. A comprehensive revision is carried out with all four Member Countries; the scope is expanded to eight technical topics.
  6. Sep 2022
    Endorsed. The MRC Joint Committee and Council endorse the updated PDG 2022.
  7. Feb 2023
    Published. The PDG 2022 is released and the phased dissemination programme begins.
  8. 2023
    National dissemination. National dissemination meetings are held across the four Member Countries.
  9. 2024
    Thematic training. Training on riparian communities and livelihoods, with a site visit to Pak Ou village.
  10. 2025
    Dam safety workshop. A Regional Training Workshop on Dam Safety, with a site visit to Nam Ngum 1 Dam.
  11. 2026
    Resource Hub launch. Member Countries recommend, and the MRCS launches, this PDG Resource Hub.

PDG & the PNPCA

Preliminary design guidance for proposed mainstream dams in the LMB : This provides initial design guidance in the form of performance targets, design, and operating principles for impact mitigation measures in key areas such as hydrology, sediment, water quality, fisheries, navigation and dam safety. It may be used by developers during project preparation and then by the MRC to assess projects through its Procedure for Notification, Prior Consultation and Agreement (PNPCA).