The Performance of Natural Flood Management at the Large Catchment-Scale: A Case Study in the Warwickshire Stour Valley

Round 1

Reviewer 1 Report

Many thanks for the effort of the authors. However, I did not see much innovation in the manuscript (MS). Almost half of the MS is allocated to model calibration and the rest regards to implementing some measures for flood control. This is not enough for a scientific paper. I suggest to highlight more ‘Natural Flood Management’, its paradigm, how stockholders were engaged?, how you could get their consensus regarding the NFM measures?, etc. These recommendations are also more aligned with the scope of WATER journal. 

Author Response

The authors thank the reviewer for their time and valuable reflection of the paper. Whilst we agree that engagement is a critical (and ongoing) evidence gap around nature-based solutions/natural flood management, this paper is principally concerned with the assessment of performance which is also another critical evidence gap. However, the authors acknowledge the critical role of engagement and obtaining consensus, and therefore, referenced this on-line 63-68. “Furthermore, land managers are often not consulted during these modelled studies, and therefore follow up engagement (and further refined modelling) is required to understand the performance of such a scheme – if modelled at all (Johnson et al. 2018, Lavers and Charlesworth 2016). Uniquely, this study engaged landowners prior to modelling, to test the realistic co-designed NFM scenario, presented in Lavers and Charlesworth (2016), in order to encourage a greater likelihood of uptake.” This includes reference to our previous paper where the authors shared their method, lessons learned around engagement and obtaining consensus with land managers (Lavers and Charlesworth 2016). 

Author Response File: Author Response.pdf

Reviewer 2 Report

The increasing stochasticity of hydrological phenomena being the effect of climate change is imposes on hydrologists the need to change the paradigm of flood management from Mechanistic to Natural Flood Management (NFM).

The paper by Lavers et al. introduces the results of models on how NFM is efficient in a large catchment scale. The authors demonstrate that when a flood severity increases, NFM diminishes significantly (which in fact was demonstrated in earlier papers, as a “seat belt effect”, which means that seatbelts are efficient up to 100 km/h and in higher speeds, their efficiency decreases drastically). However, the delayed time of flood peak was observed which provides opportunity for downstream communities to undertake flood prevention actions. However, in the lower parts of the catchment, natural floods model demonstrated significant reduction of downstream flood risk.

The paper recommended some before/after control impact monitoring programs which should be fine-tuned for every catchment due to its diversity in geology, land use and urbanization characteristics.

The paper is clearly written, however if authors would consider et least in the discussion referring to the principles of ecohydrology as a framework for optimization all range of Nature-Based Solutions for flood reduction e.g. increase in complexity of landscape, land/water ecotones, phytotechnology, this will significantly increase its inspiring role for further research on this very important challenge.

Author Response

The authors thank the reviewer for their time and valuable reflection of the paper. We particularly appreciate the critical reference to ecohydrology. Before your comment, we considered this interdisciplinary scientific field to have little reference in UK NFM literature, particularly in some of the larger evidence reviews referenced in the paper. Hopefully our inclusion of ecohydrology in lines (581 - 588) help to strengthen the need for alignment between NFM/nature-based solutions and ecohydrology studies, particularly in the field of optimising NFM for greatest, multiple-benefits. Furthermore, ecohydrology is an international concept that supports the NFM approach assessed in this study: using the understanding of relationships between hydrological and biological processes at different scales to reduce hazards from flooding to droughts, whilst enhancing biodiversity and further opportunities for sustainable development, maximizing greater harmony within catchment processes (UNESCO 2022). The complexities of biological and hydrological interactions (especially at larger hydrological scales), and their influence on hydrological response is a critical area for further research to better optimise NFM and nature-based solutions. 

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper described the application of a coupled modelling methodology to the upper Stour Valley, Warwickshire-Avon, UK.  Results of the study may have important application in the rea of flood management.  Authors may wish to consider the following in revision of their manuscript.

1.        Please comment on the effect of the characteristics of catchment on the application of the proposed model.

2.       March 2016 data was used in calibration of proposed model.  Please comment on effect of use data from different time period will have on the application of model.

3.       Please compare your proposed model with other commonly used models reported in the literature.

4.       Please discuss the cost aspect of natural flood management measures.  Please discuss on the cost and benefits of natural flood management measures.

5.       Please comment on whether the proposed model can be applicable to other catchment areas.

Author Response

The authors thank the reviewer for their time and valuable reflection of the paper. We have made the following amendments in line with your suggestions, see responses to each point below. 1. Please comment on the effect of the characteristics of catchment on the application of the proposed model. Line 171 – 175 added in methodology section: …the model build was developed to be appropriate to the catchment it was simulating, with critical characteristics of changing land cover (roughness) and infiltration (soil type) represented. 2. March 2016 data was used in calibration of proposed model. Please comment on effect of use data from different time period will have on the application of model. Line 220 - 227 added in calibration section: However, it should be noted that calibrating a model using an event from a different (earlier) time- period than the layers within the simulation will have implications on the reliability of the output. Ideally, both the remotely sensed DTM layer and land cover data would also available be for the same March 2016 period to reflect the catchment characteristics during the time of the event. Unfortunately, this period was unavailable, but the lack of temporal difference between the catchment characteristics and calibrated storm is a common limitation when conducting calibration (SEPA 2018). 3. Please compare your proposed model with other commonly used models reported in the literature. Line 158 - 162 – added to method section: The integration of 1D and 2D environments in this study model is common practice when representing whole catchment processes. For example, a coupled modelling approach consisting of Dynamic TOPMODEL, HEC-RAS, and Infoworks Integrated Catchment Modeller (ICM) models was used to characterise the response from a small (<10km2 ) catchment by Ferguson and Fenner (2020). 4. Please discuss the cost aspect of natural flood management measures. Please discuss on the cost and benefits of natural flood management measures. Whilst the appraisal of NFM costs vs benefits is a critical evidence gap, it has not been explored in this study. There is increasing literature sources reporting ‘rule of thumb’ capital costs of different measures, e.g. CIRIA 2022 NFM manual, CREW 2016 Rural SuDS Manual and Burgess-Gamble et al. (2018), but there are a considerable number of other factors that influence the cost of a measure, e.g. value of the land according to the farmer, maintenance costs associated with farmer, if maintenance is funded via a wayleave or commuted sums (like SuDS), the costs provided by contractors regarding materials, access etc. Furthermore, this study did not investigate the number of properties benefited and associated depths with different events to inform depth-damage curves used to provide a monetary value of benefits according with common appraisal methodologies in FCERM, e.g. the multi-coloured manual (Penning-Rowsell et al. 2013). However, lines (627 - 633) have included reference to the future research needed on economically appraising the whole life costs and whole life/multiple benefits of NFM to better understand their value. The study also recommends further investigation into appraising the costs and benefits of the modelled and co-designed NFM scheme. The monetary appraisal of NFM is a critical evidence gap limiting uptake, particularly in relation to whole life costs (when accounting for maintenance) and whole life multiple benefits, particularly as many NFM measures are purported to increase in effectiveness as they establish (e.g. tree planting, river restoration). Therefore, more observed data on whole life performance enabled through monitoring would provide a more robust basis to understand costs and benefits. 5. Please comment on whether the proposed model can be applicable to other catchment areas. Lines (174 - 176) included. This also enables the model build data sources and processes to be suitable for other large rural, dendritic basins.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thanks

I feel, the responses to my comments have received enough attention in the new version.

 

Author Response

Thank you for your review and comments.