Decision-Support System for LID Footprint Planning and Urban Runoff Mitigation in the Lower Rio Grande Valley of South Texas

Round 1

Reviewer 1 Report

Attached you can find comments

Comments for author File: Comments.pdf

Author Response

The authors would like to thank the reviewer for taking his/her time out to suggest some necessary improvements for the present manuscript.

Point 1: In general, the manuscript dealt with a very interesting topic showing the application of a robust model and gives some interesting suggestions about the methodology of calibration and the results that could be expected. However, I think that the study is too focused on the study case, i.e. the Lower Rio Grande Valley, for a scientific paper. On one hand, I suggest to move the description of the study site (that now is “located” at the beginning of the introduction) to a specific section after the title “Materials and Methods”, attempting to largely modify the introduction to emphasize the state-of-the-art regarding the methodologies to identify the priorities, the localization and the “hydrological performance” of urban green infrastructures that could be added to the urban landscape. On the other hand, I do not understand why the authors did not include a map describing the study case (maybe, it is interesting to give an idea about the urbanization and the green space, where it is possible to implement LID solutions).

According to my opinion, this manuscript needs additional work to merit a publication. I think that the introduction and part of the discussion must be improve with a more detailed state-of-the-art and some comparisons with other studies. Thus, I recommend the major revision that has to be a step to enrich and to reinforce the message for the publication.

Response: As per the reviewer’s suggestion, the authors moved the description of the study site in a specific section “Study Case” under the title “Materials and Methods”. The introduction was almost completely revised to emphasize more of the problem statement, state-of-the-art (regarding the methodologies used in recent times to identify the priorities, locations, and ecosystem services of LID practices within an urban watershed), knowledge gaps, and research needs. The authors also improved the paragraph about the objectives of the study. 

In the “Discussions” title, the authors added some comparisons of the results achieved in the present study with previous studies that investigated the hydrological performance of LID BMPs.

The authors also added a map in the “Study Case” section describing the study area and monitored BMP sites.

Point 2: Line 19: "to assist in eliminating...". The sentence is not clear, please re-phrase.

Response: The sentence has been rephrased as follows in the revised manuscript.

Line 17-21: “The study developed a decision support system (DSS) in the Lower Rio Grande Valley region of South Texas for optimal selection of Best Management Practices (BMPs) for substituting a portion of the WP footprint with three regionally-promising low impact development practices, such as porous concrete pavement (PCP), bioretention (BR), and bioswale (BS).”

Point 3: Line 20: "three low impact development practices". Why did the authors select these three LIDs?

Response: Under the TCEQ sponsored Clean Water Act 319 LRGV LID implementation project, flow data was monitored from six BMPs initially (which also included a green roof, constructed wetland, and permeable walking trail).  From our field assessment, porous pavement, bioretention, and bioswale were found “most promising” in terms of peak flow and runoff volume reduction in the semi-arid climatic condition of LRGV in South Texas. Besides, data collected from these three BMPs were more consistent to reveal satisfactory calibration and validation results (R² > 0.90, validation error < 30%) among all modeled BMPs. Therefore, these three were prioritized in the development of the tool.

The authors added some parts of the above explanation in the “Study Case” section.

Point 4: "assist" to "support". I think that the term "assist" is not correct.

Response: The authors corrected the term “assist” to “support”, as per the reviewer’s suggestion.

Line 27: “adoption of DSS might support better planning of the urban stormwater management in the LRGV.”

Point 5: In my opinion, the "Introduction" has to deal with the main issue of the manuscript and to answer to a series of general questions: - what is the problem? - which are the consequences? - how should it be possible to solve the problem? - which is the state-of-the-art? - which is the most common solution? - which are the objectives?. In this manuscript, the authors - first - introduced the study case. In general, I believe that a scientific work should not be only a report describing a local situation and the adopted solution, but also must propose a methodology/strategy that can be applied in other parts of the world. So, I should modify the introduction (more focusing on the issue "LID") and move this part in a specific section "Study case".

Response: The authors separated the “Introduction” title into 7 paragraphs to address the reviewer’s comments on specific research questions.

First paragraph (Line 32-41): Problem statement & consequences

Rapid urbanization and industrialization have significantly fueled the total percentage of impervious land cover (such as traditional parking loads, driveway, sidewalk, roofs, etc) within the major watersheds of the United States (US), [1–4]. Unban land developments have been increased four times in between……………………………….Stormwater Task Force Partners (STFs).

Second Paragraph (Line 42-50): What is the most common solution?

In most US states the conventional approach……………..to reduce non-point source pollutants, mitigate localized flooding in urban, colonial, and rural settings, and improve water quality [13].

Third Paragraph (Line 51-65): how should it be possible to solve the problem?

The implementation of Low Impact Development (LID) – Best Management Practices (BMPs) – have been encouraged to promote…………………………………..The recent challenge is to decide how to plan those LIDs effectively within the development boundary to meet the storm discharge goal from a boundary of commercial development.

Fourth Paragraph (Line 66-92): State-of-the-art

Several DSSs were developed as a tool to compare and evaluate the LID different ………………………. location strategies within the watershed, both spatially-known and unknown [29].

Fifth Paragraph (Line 93-114): Knowledge gaps and research needs

Previous studies evaluated the performance of LID systems to be location dependent. Several factors can affect the LID effectiveness depending……………….. in series through innovative planning, management, and engineering approaches will not only benefit communities, but it will also protect water quality and ecosystems of the watershed [11,36].

Sixth Paragraph (Line 115-132): WinSLAMM,

Source Load Assessment and Management Model for Windows (WinSLAMM) is a unique Stormwater Quality Modeling Tool……………… can be summarized per month and incorporated into the SWAT model and Geographic Information System (GIS) Platforms [38,41–43].

Seventh Paragraph (Line 133-146): Novelty in the present research, objectives, and scopes

To address the water quality issues in the US-Mexico border associated with non-point source pollution in the Lower Rio Grande Valley (LRGV) region …………………adequate, a similar algorithm can be applied to other impaired watersheds in the US and the rest of the world.

Point 6: Lines 32-71: According to my opinion, this portion of the manuscript should be titled as "Study case", and not properly an introduction of the topic.

Response: As per the reviewer’s suggestion, the authors moved the description of the study site in a specific section “Study Case” under the title “Materials and Methods”.

Line number: 149-166

Point 7: Line 72: "LID or Green Infrastructure..." The introduction should begin with these words.

The authors agreed to start the introduction with the problem statement and its consequences describing how rapid urbanization triggers uncontrolled runoff and water quality impairment in the US rivers.

Response: In the third paragraph, the authors discussed the LID as a promising tool in urban runoff control.

Point 8: Line 82: "many selection factors..." I should use the term "disciplinary" such as hydrology (stormwater reduction), ecology, healthy (air and water pollution), urban landscape (social activity), etc.

Response: As per the reviewer’s suggestion, the sentence has been revised as follows:

“Due to the variation of each watershed character, there are many disciplinary factors, such as hydrology (stormwater runoff reduction), ecology, healthy (air and water pollution), urban landscape (social activity), etc.”

Point 9: Line 94: "In dealing with the complex issues...". Here, I should integrate the manuscript with a more detailed state-of-the-art. I suggest some works focusing on the identification of priority/locations for planning the LID. For example: - multidisciplinary approaches (Charoenkit and Piyathamrongchai, 2019; Miller and Montalto, 2019; Wilker and Rusche, 2014), – hydrological modeling (Epps and Hathaway, 2019; Ercolani et al., 2018; Labib, 2019; Martin-Mikle et al., 2015; Meerow and Newell, 2017; Walaszek et al., 2018), - pollution reduction (Masseroni et al., 2018).

Response: As per the reviewer’s suggestion, the authors integrated the manuscript with a more detailed state-of-art after the statement “In dealing with complex issues….” with the reference of some recent works suggested on hydrological modelling and multidisciplinary approaches identifying priorities/locations for LID planning.

Line number: 66-92

Point 10: Line 97: "unique". Before this sentence, the authors should complete a detailed (complete) state-of-the-art. For example, I believe that Storm Water Management Model (SWMM) has similar abilities both in terms of predicting stormwater runoff and estimating pollution loads associated.

Response: The authors eliminated the term “unique” from the sentence. In the revised manuscript, the authors referred a few papers highlighting the state-of-the-art of incorporating modeling softwares such as SWMM, GIS, and machine learning algorithms in the development of a LID decision-support system.

Point 11: Line 117: "this project" of "the present work"? This term was repeated many times, and it give an impression that the manuscript is a report of a project and not a scientific work.

Response: The term “project” was replaced by the term “study” throughout the manuscript.

Point 12: Lines 116-126: I should expand the part of the introduction dedicated to the objective underlining which is the main purpose of the work and which are the secondary objectives.

Response: The author dedicated a separate paragraph to underline the objectives (preliminary and primary purpose of the study) and scopes of the present study. Some parts were revised as follows.

Line 137-146: “The preliminary objective of this study is to generate calibrated BMP models of three LID BMPs (porous concrete pavement, bioretention, and bioswale) using WinSLAMM for the semi-arid climatic region of LRGV in South Texas. The primary objective is to apply BMP models to establish a novel methodology for the DSS development and assess its feasibility in determining the footprint of an individual BMP or BMPs in series as well as their hydrologic performance (peak flow, runoff volume reduction) for a range of sizes of commercial developments. In a broader picture, this novel algorithm is expected to evaluate existing BMP footprint requirements or seek LID options as an alternative to existing or conventional facilities (e.g. wet detention pond). If the tool proves adequate, a similar algorithm can be applied to other impaired watersheds in the US and the rest of the world.”

Point 13: Line 137: Why did the authors select permeable pavements, bioretention and bioswale as elements to be studied?

Response: Among all BMPs studied under TCEW Clean Water ACT 319 project, three BMPs, such as porous pavement, bioretention, and bioswale, were found “most promising” in terms of peak flow and runoff volume reduction in the semi-arid climatic condition of South Texas. Besides, data collected from these BMPs were more consistent to reveal satisfactory calibration and validation results (R² > 0.90, validation error < 30%) among all modeled BMPs. Therefore, these three were prioritized in the development of the tool.

The authors added a paragraph in the “Study Case” section to highlight above explanation (Line 148).

Point 14: Line 143: Why should the figure "demonstrate" the framework?

Response: The term “demonstrate” has been replaced by “show” to avoid confusion.

Line 175-191: In the first paragraph of the section “2.2. DSS framework for LID footprint planning and evaluation”, the authors explained DSS inputs/outputs, methodology of algorithm development. With the Figure 2 in the revised manuscript, the authors summarized the basic structure/framework of the tool in the form of a flowchart.

Point 15: Line 144: "project" Why did the authors continue to cite the "project"?

Response: The term “project” was eliminated or replaced by the term “study”

Point 16: Figure 1: the figure simply describes the framework of the work. To improve the quality of the figure, the authors should underline which are the input parameters, which are the developed methods, and which are the output. I should use a different shapes of the box to underline such categories.

Response: According to the reviewer’s suggestion, the authors used a different shape of boxes to underline input/output and process categories, which has been defined in a footnote after Figure 1, such as the following (Line 193):

All parallelogram-shaped boxes represent input/output parameters.

All square-shaped boxes represent a process.

Point 17: Section 2.3: This section seems to be a user manual. How did the authors generate the site-specific rainfall (design hyetograph or time-series of precipitation based on future prediction?)?

Response: The authors followed the “WinSLAMM calibration manual” for the hydrologic calibration of BMP models. In Section “2.4. WinSLAMM Model Development”, the authors described first how they prepared the model input files.

Unlike the other hydrological models (e.g. SWMM), WinSLAMM does not allow the direct input of User-Defined hyetograph or time series of rainfall. This model only allows users to enter the daily distribution of rainfall in a “Rainfall File Editor” table of the model.

The authors first retrieved rainfall data from the rain gauge installed at each monitored site and analyzed using FlowLink software. Then, the authors entered the daily rainfall data in the editor to create a site-specific rainfall file. This editor takes input, such as the date of the rainfall event, rainfall start time, end time, total duration, total rainfall depth, intensity, and time between two consecutive rainfall events. Please see the screenshot of the Rainfall editor.

Please see the attached screenshot of the “Rainfall File Editor” in WinSLAMM:

Point 18: Line 182: "goodness of fit" According to my opinion, r2 and NSE are very similar. I suggest using different scores, often used in hydrological literature. An example is the KGE.

Response: As per the reviewer’s suggestion, the authors used KGE scores to assess the goodness of fit of the model. Accordingly, all texts reporting the statistical values in the sections “2.4. WinsSLAMM model Development” and “3.1. WinSLAMM-Calibrated BMP Model Development”.

To avoid repetition, all statistical values from Figure 3 have been deleted.

Point 19: Line 197: "subtraction of volumetric evaporation". Please, more details.

Response: The sentence has been revised as follows.

“For the uncontrolled or baseline condition, the peak discharge from a rainfall event was calculated by taking the difference between discharge calculated by the rational method and the volumetric evaporation rate (rate of evaporation, mm/h × total area of commercial development, m²).”

Point 20: Line 201: "&" to "and".

Response: The “&” has been corrected to “and” in the revised manuscript.

Point 21: Figure 2: The flowchart seems to be a list. Figure could be improved or removed.

Response: The authors agreed to remove Figure 2 (old manuscript) in the revised manuscript.

Point 22: Line 251: "demonstrates" to "shows".

Response: The term “demonstrates” has been replaced by “shows” in the revised manuscript.

Point 23: Line 263: "A total of 14 significant rainfall events". I should add a table with period of monitoring, number of rainfall events, average of characteristics of rainfall events, max rainfall depth, calibrated parameters and performance indexes.

Response: As per the reviewer’s suggestion, a table has been added with a period of monitoring, the number of rainfall events, max rainfall depth, normalized volume reduction, and calibrated parameters.

To avoid repetition, the authors deleted the calibration parameters from Figure 3.

Point 24: In this section, I should attempt to compare one of the main results of the present manuscript, i.e. the high rate of rainfall reduction. I think that the hydrological literature that investigated the hydrological "performance" of green roofs (or other green infrastructures) is rich and wide (Masseroni and Cislaghi, 2016) parameters and performance indexes.

Response: As per the reviewer’s suggestion, the authors compared results of the present work with four previous studies that investigated the hydrological performance of LID BMPs. The authors cited the following four papers in the “Discussion” title to discuss how the results of the present manuscript differ from the results from other studies:

Collins, K.A.; Hunt, W.F.; Hathaway, J.M. Hydrologic Comparison of Four Types of Permeable Pavement and Standard Asphalt in Eastern North Carolina. Journal of Hydrologic Engineering 2008, 13, 1146–1157.

Purvis, A.R.; Winston, J.R.; Hunt, F.W.; Lipscomb, B.; Narayanaswamy, K.; McDaniel, A.; Lauffer, S.M.; Libes, S. Evaluating the Water Quality Benefits of a Bioswale in Brunswick County, North Carolina (NC), USA. Water 2018, 10.

Masseroni, D.; Cislaghi, A. Green roof benefits for reducing flood risk at the catchment scale. Environmental Earth Sciences 2016, 75, 579.

Zhang, X.; Hu, M. Effectiveness of Rainwater Harvesting in Runoff Volume Reduction in a Planned Industrial Park, China. Water Resources Management 2014, 28, 671–682.

The authors added the following talking points in “Discussions” title in the revised manuscript:

“Our present study in the semi-arid climatic LRGV observed comparatively higher normalized runoff volume reduction from PCP than the eastern sub-tropical, humid part of the US (e.g. North Carolina), where the reduction was calculated as low as 0.008 ± 0.006 m³/m² [58]. This comparison indicates that our established DSS algorithm might predict higher space requirements for the same BMPs in sub-tropical climates.”

“The performance of our monitored bioretention in the semi-arid LRGV was even higher than that for the sub-tropical state of Virginia, US, where normalized volume reduction was calculated as 0.11 ± 0.23 m³/m² [65].”

“A study in Italy showed that a single green roof with 100% green conversion could achieve runoff volume reduction up to 35% [66]. Our DSS predicted that WP, PP, BR, or BS alone might achieve more than 75% runoff reduction with the green conversion of 31%, 51%, 23%, and 18%, respectively. These results indicate a greater hydrologic potential of these four BMPs than the green roof.”

“However, Zhang & Hu [67] observed the most promising runoff volume reduction (up to 100%) from rainwater harvesting cistern in China in the cases of critical rainfall storm (50 mm).”

Point 24: I appreciate the list of main outcomes of the present study.

Response: Thanks for the reviewer’s appreciation.

Point 25: I think that the references are poor. There are too technical reports, and less scientific papers. I suggest searching additional works (I should suggest some reviews).

• Additional references

Charoenkit, S., Piyathamrongchai, K., 2019. A review of urban green spaces multifunctionality assessment: a way forward for a standardized assessment and comparability. Ecol. Indic. 107, 105592. https://doi.org/10.1016/j.ecolind.2019.105592

Epps, T.H., Hathaway, J.M., 2019. Using spatially-identified effective impervious area to target green infrastructure retrofits: a modeling study in Knoxville, TN. J. Hydrol. 575, 442–453. https://doi.org/10.1016/j.jhydrol.2019.05.062

Ercolani, G., Chiaradia, E.A., Gandolfi, C., Castelli, F., Masseroni, D., 2018. Evaluating performances of green roofs for stormwater runoff mitigation in a high flood risk urban catchment. J. Hydrol. 566, 830–845. https://doi.org/10.1016/j.jhydrol.2018.09.050

Gwenzi, W., Nyamadzawo, G., 2014. Hydrological Impacts of Urbanization and Urban Roof Water Harvesting in Water-limited Catchments: A Review. Environ. Process. 1, 573–593. https://doi.org/10.1007/s40710-014-0037-3

Labib, S.M., 2019. Investigation of the likelihood of green infrastructure (GI) enhancement along linear waterways or on derelict sites (DS) using machine learning. Environ. Model. Softw. 118, 146–165. https://doi.org/10.1016/j.envsoft.2019.05.006

Martin-Mikle, C.J., de Beurs, K.M., Julian, J.P., Mayer, P.M., 2015. Identifying priority sites for low impact development (LID) in a mixed-use watershed. Landsc. Urban Plan. 140, 29–41. https://doi.org/10.1016/j.landurbplan.2015.04.002

Masseroni, D., Cislaghi, A., 2016. Green roof benefits for reducing flood risk at the catchment scale. Environ. Earth Sci. 75. https://doi.org/10.1007/s12665-016-5377-z

Masseroni, D., Ercolani, G., Chiaradia, E.A., Maglionico, M., Toscano, A., Gandolfi, C., Bischetti, G.B., 2018. Exploring the performances of a new integrated approach of grey, green and blue infrastructures for combined sewer overflows remediation in high-density urban areas. J. Agric. Eng. 49, 233–241. https://doi.org/10.4081/jae.2018.873

Meerow, S., Newell, J.P., 2017. Spatial planning for multifunctional green infrastructure: Growing resilience in Detroit. Landsc. Urban Plan. 159, 62–75. https://doi.org/10.1016/j.landurbplan.2016.10.005

Miller, S.M., Montalto, F.A., 2019. Stakeholder perceptions of the ecosystem services provided by Green Infrastructure in New York City. Ecosyst. Serv. 37, 100928. https://doi.org/10.1016/j.ecoser.2019.100928

Walaszek, M., Bois, P., Laurent, J., Lenormand, E., Wanko, A., 2018. Urban stormwater treatment by a constructed wetland: Seasonality impacts on hydraulic efficiency, physico-chemical behavior and heavy metal occurrence. Sci. Total Environ. 637–638, 443–454. https://doi.org/10.1016/j.scitotenv.2018.04.325

Wilker, J., Rusche, K., 2014. Economic valuation as a tool to support decision-making in strategic green infrastructure planning. Local Environ. 19, 702–713. https://doi.org/10.1080/13549839.2013.855181

Response: The authors referred to several scientific papers in the revised manuscript, which also included most of the papers suggested above by the reviewer.

Author Response File: Author Response.pdf

Reviewer 2 Report

Various previous studies related to the optimal layout of the LID facility have been carried out. Describe the differences and strengths of the developed models in this study.

The efficiency of the LID facility can be expressed as reduction of peak flow, total volume, and cost. Please describe how you selected the best alternative to reflect these.

How can continuous rainfall (with double or more peaks) be reflected to determine the optimal alternative?

How can long-term reductions be reflected, rather than single rainfall event?

Author Response

The authors would like to thank the reviewer for taking his/her time out to suggest some necessary improvements in the present manuscript.

Point 1: Various previous studies related to the optimal layout of the LID facility have been carried out. Describe the differences and strengths of the developed models in this study.

Response: The authors added the following paragraphs in the “Introduction” title to discuss previous studies (with strengths and differences) related to the optimal planning of LID layout through identifying priorities/locations for maximizing hydrological benefits.

Previous studies and their strengths

Line 66-92: “Several decision-support systems were developed as a tool to compare and evaluate different LID scenarios within the watershed boundary [20]. A study developed a tool for the placement of LID based on the defined precipitation and soil moisture conditions. Results showed the areas that are the most suitable location for LID installments and the optimal facility with higher retention abilities of the accumulated runoff [21]. Another study developed an algorithm to allow the selection of LIDs with the lowest cost, highest runoff reduction and the highest likelihood of private-owner maintenance in various sub-watersheds [22]. Another similar study developed a decision-making tool by evaluating various alternatives to determine the most cost-effective types and combinations of LIDs that maximize the water quality benefits [23]. In dealing with the complex issues in stormwater management, the use of decision support systems supported by modeling tools is becoming increasingly popular [24]. Analyzing LID through coupling modeling software with a multi-objective optimization using genetic algorithms has been a common method [20,25]. Ercolani et al. [26] used the MOBIDIC-U hydrologic model equipped with SMART-GREEN (a QGIS plugin interface) to study the effects of green roofs in an urban watershed. Their study revealed that green roofs might work better under frequent and smaller magnitude storms and their efficiency can be increased with spatially heterogeneous implementation. Martin-Mikle et al. [5] presented a spatially-explicit method using GIS for the placement LID within the urban watershed to increase the cost-effectiveness and ecological benefits. Meeorw & Newell [27] developed a Green Infrastructure Spatial Planning (GISP) model to aid in identifying trade-offs, synergies, and hotspots for future GIs with maximum ecosystem services. Charoenkit & Piyathamrongchai [28] developed a framework for the comparative assessment of multifunctionality among different urban ecosystem structures. A previous study evaluated a machine learning approach using artificial neural network (ANN), adaptive network-based fuzzy inference system (ANFIS) algorithms, and statistical modeling to predict the probability of green or grey transformation for vacant places, poor condition sites, and waterway corridors [29]. Previously, SWMM-calibrated GI models were used to assess runoff reductions via different location strategies within the watershed, both spatially-known and unknown [30].”

Differences/knowledge gaps in previous studies

Line 93-114: Previous studies evaluated the performance of LID systems to be location dependent. Several factors can affect the LID effectiveness depending on the type, design and local conditions such as the topography of the site, soil type/conditions, rainfall patterns and other types of hydrological and meteorological properties [31]. Due to the variation of each watershed character, there are many disciplinary factors, such as hydrology (stormwater runoff reduction), ecology, healthy (air and water pollution), urban landscape (social activity), etc. The guidelines for BMPs planning are not consistent even within neighbouring cities due to the hydro-geological variation. For example, stormwater runoff generated from a 25-year frequency storm event in new commercial development in San Benito, Texas, is generally required to be detained on-site, to release into a receiving system at a 25-year predevelopment discharge rate. On the other hand, the city of Weslaco followed more stringent drainage policies of 10-years predevelopment discharge rate because of its lower elevation [32]. Most of the previous studies focused on the development of a framework for identifying the optimal distribution of BMPs within the mix-used watershed for maximizing ecosystem services [5,30]. The previous study also prioritized economic evaluation as a decision support tool for strategic spatial planning of GIs [33]. Very few studies have attempted to develop a region-specific decision-support framework to assess the LID transformation in a small-scale or commercial development boundary to reveal both maximum ecosystem services and minimum costs. Still, there is a lack of having a well-established tool to enforce the local drainage policy in optimal selection and evaluation of combined BMP scenarios for maximizing hydrologic benefits in urban development [34,35,30] The proper selection of BMP or BMPs in series through innovative planning, management, and engineering approaches will not only benefit communities but will also protect water quality and ecosystems of the watershed [11,36]. The present study was designed to develop an innovative Decision Support System (DSS) for the planning of BMP(s) footprint to replace a portion of conventional detention practices with LID echo-technologies. The preliminary objective of this study is to generate calibrated BMP models of three LID BMPs (porous concrete pavement, bioretention, and bioswale) using WinSLAMM for the semi-arid climatic region of LRGV in South Texas. The primary objective is to apply BMP models to establish a novel methodology for the DSS development and assess its feasibility in determining the footprint of an individual BMP or BMPs in series as well as their hydrologic performance (peak flow, runoff volume reduction) for a range of sizes of commercial developments. In a broader picture, this novel algorithm is expected to evaluate existing BMP footprint requirements or seek LID options as an alternative to existing or conventional facilities (e.g. wet detention pond). If the tool proves adequate, a similar algorithm can be applied to other impaired watersheds in the US and the rest of the world.

Point 2: The efficiency of the LID facility can be expressed as reduction of peak flow, total volume, and cost. Please describe how you selected the best alternative to reflect these.

Response: Thanks for your comments. The authors discussed the selection process of the best LID alternative in the following sections.

Single BMP option:

Peak Flow: Our development LID decision support algorithm predicted that a single wet detention pond of 1.22 ha might efficiently handle 50-years frequency storm event from a 4 ha of commercial development (peak inflow ~ 0.53 m³/s) in Brownsville, Texas, which can release the least peak outflow of 0.034 m³/s with maximum flow reduction of 94%. DSS predicted that bioswale alone might require the least footprint area to meet 10-years frequency targeted discharge (0.12 m³/s) with the peak outflow rate of 0.113 m³/s. On the other hand, bioretention alone might induce a similar rate of peak outflow (0.046 m³/s) to a wet pond with much less land utilization (0.93 ha) than porous concrete pavement and wet pond.

Total volume reduction: Although wet pond might be beneficial to control runoff volume with a maximum reduction of 94%, the land utilization might be as high as 1.22 ha. On the other hand, bioretention might show similar performance (90-95% reduction) with less land utilization of 0.93 ha than a wet pond and porous concrete pavement in a 4-5 ha commercial development in Brownsville, TX

Cost: Our development LID decision support algorithm predicted that a single wet detention pond might cost as high as $16 M (including construction, O&M, and others) to handle a 50-years frequency storm event from a 4 ha of commercial development in Brownsville, Texas. On the other hand, Porous Concrete Pavement, Bioretention, and bioswale might cost close to $3.5M, $3.6 M, 1.6M, respectively.

Selection of the best alternative: Considering DSS predicted hydrological benefits and cost, bioretention alone might be the optimal option from any commercial development in Brownsville, TX, however.

Combined BMPs option:

Total volume reduction & cost: In terms of volume reduction, a combination of PCP, BR, BS, and WP in series might require the least construction cost of $7.5M with runoff reduction of 78%. By incorporating this combination, the serviceability and property value of the site can be increased. DSS also predicted a combination of BR (0.47 ha), BS (0.36 ha), and WP (0.84 ha) in series, which might be the most promising to handle 50-years frequency storm event runoff reduction up to 100% from a 4 ha commercial development with a total cost of $9 million approximately. Besides, this combination can improve land use management and foster healthy aesthetics on the site.

Selection of the best alternative: Considering all hydrological benefits and costs, a combination of bioretention bioswale, wet detention in series might be optimal for combined BMP cases for any commercial development in the LRGV region.

The above findings and explanations have been added in different paragraphs of the “Discussions” and “Conclusions” titles.

Line number 448-452

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Line number 473-476

Line number 479-487

Point 3: How can continuous rainfall (with double or more peaks) be reflected to determine the optimal alternative?

Response: This is a good research question. A drainage site with a complex land-use surface often exhibits multi-peak hydrographs characterized by two discharge peaks for a single storm. The first peak corresponds to the first flush runoff from the impervious surfaces, while the rest of the peaks correspond to both impervious and natural pervious surfaces (Gwenzi and Nyamadzawo, 2014). Unlike the other hydrological models (e.g. SWMM), WinSLAMM does not allow the direct input of User-Defined Hydrographs to fit the observed multiple peaks for calibration purposes. This model only allows users to enter the daily distribution of rainfall instead of the time distribution of the rainfall or hyetograph, which can be one of the limitations of the WinSLAMM.

Source: http://www.winslamm.com/faq.html

WinSLAMM calibrates the runoff volume by using the runoff coefficient as the most sensitive calibration parameters. As an outcome, the model approximates the composite peak flow from the first flush runoff generated within complex drainage surfaces (impervious, pervious, semi-pervious, etc.). In our present study, those composite peak flow values were used to generate the DSS algorithm. Thus, our DSS might not effectively reflect continuous rainfall (with double or more peaks) to determine the optimal alternative. Therefore, the authors recommended the tool more as a planning tool rather than a scientific tool dealing with deep-theories or mechanisms. Future works can be recommended to emphasize calibrating hydrograph based on the user-defined hyetograph to capture the characteristics of continuous rainfall for the development of BMP models.

Most of the parts of the above discussions have been added as a paragraph under the “Conclusions” title talking about limitations and future recommendations of the present work.

Line number 528-533

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Point 4: How can long-term reductions be reflected, rather than a single rainfall event?

Response: Observed datasets of 3 to 1 of rainfall, peak flow, and runoff volume have been used for the calibration of BMP models.

Based on the simulation of calibrated BMP models, the DSS convergence algorithm was written for the determination of footprint to deal with a 50-years frequency storm event (12.7 mm/h) as an input and 10- years frequency storm (12.7 mm/h) discharge as an output. However, the developer team is making progress to increase the robustness of the tool so that the users can select the design storm frequency from the drop-down menu. This might help to asses long term runoff reductions dealing with varying rainfall characteristics from multiple events.

The above discussions have been added in the “Conclusions” title talking about limitations and future recommendations of the present tool.

Line number 528-533

Line number 546-557

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript concerns important issue of the Decision Support System for LID Footprint Planning and Urban Runoff Mitigation. The presented Case Study concerns the Lower Rio Grande Valley of South Texas. The following suggestions should be referred to. Add references to all of the equation, in the case You are not the Author of the equations.

how in practice the results of the presented analysis can be used? This should be discussed in the point concerning discussion of the results.

Are there concrete steps that can be recommended and how generalizable are the findings?

The novelty of the distingusihed method should be underlined in the manuscript.

Author Response

The authors would like to thank the reviewer for taking his/her time out to suggest some necessary improvements in the present manuscript.

Point 1: The manuscript concerns important issue of the Decision Support System for LID Footprint Planning and Urban Runoff Mitigation. The presented Case Study concerns the Lower Rio Grande Valley of South Texas. The following suggestions should be referred to. Add references to all of the equation, in the case You are not the Author of the equations.

Response: As per the Reviewer’s suggestion, the authors added references to equation 2-7 in the revised manuscript pertinent to KGE, RMSE, rational method, and flow rate to volume calculation. However, those equations were slightly changed from their original form. Equations 1, 8-10 were formulated by the authors for the present work.

Line number 227

Line number 248-251

Point 2: how in practice the results of the presented analysis can be used? This should be discussed in the point concerning the discussion of the results.

Response: Overall, the results of the presented analysis may support planners, stakeholders, and stormwater task force partners for optimized planning, design, and implementation of LID facilities in any commercial development of the region. Considering DSS predicted hydrologic results (peak flow, runoff volume reduction) and cost, the most promising BMP or BMPs in series can be suggested at the beginning of the land development process in the semi-arid climatic region of LRGV. These results can also help to evaluate any existing/conventional facilities (e.g. wet detention pond) or to seek LID alternatives to maximize ecosystem services with a minimized cost. Furthermore, the outcomes of the tool can be incorporated into the enhancement of property development options and values in the region. Sustainable urban stormwater management will eventually lead to surface water quality improvement in the Arroyo Colorado watershed.

The above discussions have been added as a paragraph at the end of the “Conclusions” title.

Line number 493-502

Point 3: Are there concrete steps that can be recommended and how generalizable are the findings?

Response: The application of hydrologic models to develop a decision support framework is becoming popular. The authors recommend some concrete steps for this methodology:

1. Collection of field-scale hydrologic data (rainfall, duration, peak flow, runoff volume) from different LID BMPs through continuous monitoring
2. Selection of modeling tool
3. Development of regionally-calibrated BMP models
4. Simulations of calibrated models for a different set of conditions (e.g. varying rainfall intensity, varying footprint, varying size of commercial development, etc.) to generate a BMP database for the region
5. Transformation of database information into equations
6. Development of a decision-support convergence algorithm for LID planning with basic hydrologic and modeled-equations in accordance with local drainage guidelines as boundary conditions

The findings of our developed DSS will be only applicable to the LRGV region since the algorithm allows hydro-geological input from 14 cities in the region. However, a similar methodology and convergence algorithm can be applied to other impaired watersheds in the US and the rest of the world only after a regional calibration and validation of BMP models.

The above texts have been added at the very end of the “Conclusions” title.

Line number 504-507

Point 4: The novelty of the distinguished method should be underlined in the manuscript.

Response: The authors highlighted the novelty of the distinguished method at the very beginning and end of the “Conclusions” title in the revised manuscript by adding the following sentences:

Line number 504-507: “The present study established a novel methodology of a decision-support system for the planning of LID footprint using calibrated BMP models with the estimation of hydrologic performances (peak flow, runoff volume reduction) in any commercial development in the Lower Rio Grande Valley of South Texas.”

Line number 558-560: “However, a similar methodology and convergence algorithm can be applied to other impaired watersheds in the US and the rest of the world only after a regional calibration and validation of BMP models”

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors, I have appreciated the efforts to reply to all my questions. You have largely modified the structure of the manuscript as I suggest. There is only one critical point: the figure 4 is of poor quality (the font size is too small in all the subplots). I should create a unique figure with four subplots cancelling the labels of subplot 2, the xlabel of subplot1, and the ylabel of subplot 4 (and the corresponding x-y ticklabels). For this reasons, after this minor correction, I think that the manuscript will be ready for being published.

Author Response

The authors would like to thank the reviewer for his thoughtful comments and efforts towards improving the manuscript.

We updated the figure as suggested by the reviewer

Author Response File: Author Response.pdf