Reach-scale river restoration or environmental water allocation (EWA) exercises typically address the magnitude and temporal dynamics (frequency, duration, timing, rate of change) of flows required to sustain desirable ecological conditions along a river. The role of geomorphology in this process is to broaden the gaze beyond flows to consider larger and longer-term interactions between valley lithological structure, and the feed and fate of flow-sediment mixtures. This paper proposes the integration of numerical morphodynamic modelling in evaluations of environmental water requirements for non-perennial riverscapes (channel–riparian–floodplain environments). The paper presents a methodological framework, and proof of concept case study from the Touws River, South Africa, for the application of morphodynamic modelling in EWA. The paper illustrates operational approaches to modelling the complexity of dryland mixed bedrock-alluvial (and mixed-load) riverscapes with highly variable non-perennial flow regimes, including an approach to generating initial bed conditions for numerical experiments by ‘morphodynamic spin-up’, and approaches to synthesising and presenting numerical experiment output in the form of a dynamic range of potential variability in metrics of physical habitat suitability and diversity, and disturbance/renewal regimes. Such efforts can assist in enhancing field observations and testing field-based hypotheses of flow-sediment regime–physical habitat associations, extending the timescales of analysis beyond field observation, and constraining uncertainty about the dynamic range of variability in responses to predicted future flow-sediment regime modifications. Further research is needed to develop growth models appropriate for key non-perennial river vegetation types, to support biomorphodynamic modelling of geomorphology–vegetation interactions, and to determine or predict appropriate inlet sediment concentrations for historical and future modification scenarios.

达到规模的河流恢复或环境水分配（EWA）演习通常涉及维持河流理想生态条件所需的水流的大小和时间动态（频率，持续时间，时间，变化率）。地貌学在这一过程中的作用是将目光扩大到流动以外，以考虑山谷岩性结构与流动-沉积物混合物的进料和归宿之间的更大和更长期的相互作用。本文提出了对非多年生河流景观（河道-河岸-洪泛区环境）的环境需水量进行评估的形态学动力学模型的集成。本文介绍了形态学建模在EWA中的应用的方法框架和概念验证案例研究（来自南非Touws河）。本文阐述了用于模拟旱地混合基岩-冲积河（和混合负荷）河景复杂性的操作方法，该方法具有高度可变的非多年生水流态，包括通过“形态动力学旋转”为数值实验生成初始河床条件的方法，以及以物理栖息地的适宜性和多样性以及干扰/更新制度的度量中的潜在可变性的动态范围的动态范围的形式合成和呈现数值实验输出的方法。这些努力可以帮助加强现场观察，并检验基于流动的沉积物制度与自然栖息地之间联系的基于现场的假设，将分析的时间范围扩展到现场观察之外，并限制了对预期的未来流量-沉积物制度修改的响应中的动态变化范围的不确定性。需要开展进一步的研究来开发适合于关键非多年生河流植被类型的生长模型，以支持地貌-植被相互作用的生物形态动力学模型，以及确定或预测历史和未来改良情景的合适进口沉积物浓度。