Community spongy transformation design method for balancing manufacturing cost and runoff reduction

Abstract

The invention discloses a community spongy transformation design method for balancing cost and runoff reduction, and the method specifically comprises the steps: selecting a proper LID facility for a to-be-transformed region in a community according to the characteristics of the community and the to-be-transformed region; with maximization of the total rainfall runoff reduction rate and minimization of the cost as targets, constraint conditions are set, and the theoretical optimal laying area of each LID facility is calculated; and based on the theoretical optimal laying area of the ith LID facility, selecting a proper area from all areas in which the ith LID facility needs to be laid to lay the ith LID facility. By means of spongy transformation, waterlogging after rainstorm can be relieved, the environment of an old community is effectively improved, and the living experience of residents is improved; through multi-objective optimization, fund saving and reasonable resource allocation can be realized, unnecessary investment is avoided, repeated construction is reduced, and the transformation has more economic benefits; by determining the specific position and proportion of the LID facility, the construction can be accurately guided, and the construction efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy science and technology, and in particular relates to a design method for sponge city transformation of residential areas that balances construction costs and runoff reduction. Background Technology

[0002] Promoting the construction of sponge cities requires focusing on rainwater-related problems within built-up areas, prioritizing the alleviation of urban flooding, while also comprehensively reducing rainwater runoff pollution and improving rainwater collection and utilization. This should be achieved through integration with urban renewal initiatives, prioritizing urgent and phased solutions, and focusing on key issues such as waterlogging that significantly impact people's lives and livelihoods.

[0003] A sponge city refers to a city that, like a sponge, possesses good "elasticity" in adapting to environmental changes and responding to natural disasters, and also practices "Low Impact Development (LID)." Urban resilience refers to the ability to absorb, store, infiltrate, and purify rainwater when it falls, and to "release" and utilize the stored water when needed. Low Impact Development refers to the use of source-based, decentralized measures during site development to maintain the site's pre-development hydrological characteristics.

[0004] Existing research on sponge cities mainly focuses on the deployment of sponge facilities in newly built cities and the comprehensive assessment of the impact of sponge city construction on hydrological cycles and cost-effectiveness. The evaluation models using optimization algorithms are not yet fully developed. Due to construction time and historical reasons, older residential areas currently have significant drawbacks: limited green space and insufficient greening, large land area occupied by gray infrastructure, numerous waterlogging points, severe flooding, and susceptibility to pollution. There is a lack of necessary research on the sponge-based upgrades of many existing older residential areas in cities, including how to select the type and area of ​​source reduction facilities, how to deploy sponge facilities based on the characteristics of existing communities, and how to determine the specific location and proportion of LID (Low Identification and Discharge) facilities. Summary of the Invention

[0005] Purpose of the invention: In order to solve the problems existing in the prior art, the present invention provides a design method for sponge city transformation of residential communities that balances cost and runoff reduction.

[0006] Technical solution: This invention provides a design method for sponge city transformation of residential communities that balances construction costs and runoff reduction, specifically as follows:

[0007] Based on the characteristics of the community and the areas to be renovated, select appropriate LID facilities for the areas to be renovated within the community;

[0008] With the goal of maximizing total stormwater runoff reduction rate and minimizing cost, constraints are set to calculate the theoretical optimal installation area for each type of LID facility;

[0009] Based on the theoretically optimal installation area of ​​the i-th type of LID facility, select a suitable area to install the i-th type of LID facility in all areas where it is required.

[0010] Furthermore, the expression for the total stormwater runoff reduction rate is as follows:

[0011] ;

[0012] in, This represents the installation area of ​​the i-th type of LID facility. This refers to the sum of the areas within the community that are to be renovated. The runoff coefficient of all areas to be upgraded that require the installation of the i-th type of LID facility before the upgrade. To lay out an area of ​​[area] in all areas to be upgraded where the i-th type of LID facility needs to be installed. The runoff coefficient after the i-th type of LID facility.

[0013] Furthermore, the constraints are specifically as follows:

[0014] Set the maximum and minimum values ​​for the installation area of ​​the i-th type of LID facility.

[0015] If the selected LID facilities include rain gardens and permeable pavements, then set the following constraints:

[0016] ;

[0017] ;

[0018] in, This refers to the area of ​​green space within the residential community. The area to be paved for sunken green spaces. The area covered for the rain garden; For the area of ​​permeable pavement, This refers to the area of ​​roads within the residential community.

[0019] Furthermore, the theoretical optimal installation area for each type of LID facility is calculated as follows:

[0020] For the i-th type of LID facility, its initial value is set to and with Using % as a percentage, set the area value scheme for the i-th type of LID facility: × % ×( +1), ..., ...

[0021] Furthermore, for the first type of LID facility, the total stormwater runoff reduction rate and cost are calculated under all area value schemes for the first type of LID facility. Each area value scheme of the first type of LID facility is combined with all area value schemes of the second type of LID facility, and the total stormwater runoff reduction rate and cost are calculated again. This process is iterated until the last LID facility is added, and the total stormwater runoff reduction rate and cost under all combinations are obtained. With the goal of maximizing the total stormwater runoff reduction rate and minimizing the cost, the optimal combination is selected based on the actual situation.

[0022] Furthermore, in all areas where the i-th type of LID facility needs to be laid, a suitable area is selected to lay the i-th type of LID facility. Specifically, based on the area where the i-th type of LID facility needs to be laid, several area combinations are selected multiple times, such that the difference between the sum of the areas of these several areas and the theoretical optimal laying area of ​​the i-th type of LID facility is less than a preset value, and multiple combinations are obtained for the i-th type of LID facility; the optimal combination is selected.

[0023] Furthermore, the optimal combination is selected according to the following formula:

[0024] ;

[0025] in, Euclidean distance. Let be the theoretically optimal installation area for the i-th type of LID facility. I represents the actual area to be laid under several area combinations corresponding to the i-th type of LID facility, where I is the total number of LID facilities.

[0026] choose The smallest combination is the optimal combination.

[0027] Beneficial Effects: This invention balances the construction cost and stormwater runoff control rate of sponge cities by setting different combinations of LID facilities. It constructs an iterative multi-objective optimization algorithm, obtaining the optimal solution for determining the location of LID combinations after multiple iterations of "exhaustive search + Euclidean distance". The SWMM model is used to simulate the optimization results after iteration, thus demonstrating the runoff reduction effect after sponge city transformation of residential areas. The results show that sponge city transformation can reduce runoff, the constructed iterative algorithm effectively balances cost and runoff reduction, and can determine the specific location and proportion of LID facilities. This invention utilizes sponge city transformation to alleviate urban flooding after heavy rains, effectively improve the environment of old residential areas, and enhance residents' living experience. Through multi-objective optimization, it achieves a reasonable allocation of funds and resources, avoids unnecessary investment, reduces redundant construction, and makes the transformation more economical. By determining the specific location and proportion of LID facilities, it can accurately guide construction and improve construction efficiency. Attached Figure Description

[0028] Figure 1 This is an overall flowchart of the present invention;

[0029] Figure 2 This is a schematic diagram of the study area;

[0030] Figure 3 A graph showing the relationship between stormwater runoff reduction rate and investment cost;

[0031] Figure 4 A simplified diagram of the stormwater pipe network in the SWMM model;

[0032] Figure 5 Linear diagrams of rainfall events with different return periods;

[0033] Figure 6 This diagram shows the changes in the layout of LID facilities within the study area under three different scenarios. Detailed Implementation

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0035] Due to their construction time and historical reasons, older residential communities currently have significant drawbacks: limited green space and sparse greenery, large areas occupied by gray infrastructure, numerous water accumulation points, severe flooding, and susceptibility to pollution. Transforming these communities into sponge city projects offers several advantages: ① It can convert some existing impermeable gray pavements into permeable pavements to reduce surface runoff; ② It can add green roofs to reduce rooftop runoff, purify rainwater pollutants, and collect runoff through rainwater tanks or reservoirs, delaying peak runoff times and allowing for rainwater utilization during non-rainy periods; ③ It can transform existing green spaces into rain gardens and sunken green areas, increasing rainwater infiltration, filtration, and storage to reduce surface runoff and increase rainwater infiltration, delaying peak runoff times and purifying rainwater to reduce runoff pollution.

[0036] This embodiment presents a design method and system for sponge city renovation of old residential areas that balances construction costs and runoff reduction. By setting up different combinations of LID (Light Injection Discharge) facilities, it increases rainwater retention and infiltration, reducing the burden on urban drainage networks, purifying water bodies, and alleviating urban flooding and other water-related problems. To balance the construction cost of sponge cities and the rainwater runoff control rate, this invention constructs an iterative multi-objective optimization algorithm. After multiple iterations of "exhaustive search + Euclidean distance," the optimal solution for determining the location of LID combinations is obtained. The optimization results after iteration are simulated using a Swing Model (SWMM) to determine the runoff reduction effect after sponge city renovation of old residential areas and the determined location and proportion of LID facilities, providing a direct reference for the optimized design and construction of sponge cities.

[0037] The method in this embodiment is as follows: Figure 1 As shown, specifically:

[0038] Step 1: Screening of LID facilities.

[0039] Based on the characteristics of the community, suitable LID facilities were selected from existing facilities. The LID facilities were then summarized in terms of runoff control, rainwater purification capacity, construction cost, and land area requirements. The results are shown in Table 1.

[0040] Table 1

[0041]

[0042] In Table 1 above, A indicates good runoff control effect, B indicates some runoff control effect, and C indicates limited runoff control effect; rainwater purification capacity is divided into three levels, represented by a, b, and c: a indicates good effect, b indicates some or good effect, and c indicates limited effect; facility construction and maintenance costs are divided into four levels, represented by I, II, III, and IV: I indicates low cost, II indicates relatively low cost, III indicates relatively high cost, and IV indicates high cost; land area requirements are divided into three levels, represented by i, ii, and iii: i indicates small land area requirement, ii indicates some land area requirement, and iii indicates high land area requirement.

[0043] LID (Light Discharge) facilities should be deployed based on their unique characteristics and the specific needs of the target area. For example, areas prone to severe flooding require higher runoff reduction capabilities, so more LID facilities with better runoff control should be selected. In areas with severe pollution, LID facilities with good purification capabilities should be prioritized. For different primary needs, the minimum deployment ratio of corresponding facilities should be increased. For instance, if runoff reduction is paramount, facilities with strong drainage capacity should be added, and their threshold values ​​increased to achieve the best results.

[0044] Regarding the priority selection of LID facility deployment, the existing conditions and the intensity of demand are ranked, such as: the basic greening situation in a community, whether the area available for renovation in the community is sufficient, whether the building roofs meet the renovation conditions, the degree and location of waterlogging in the community during the rainy season, and whether there are black and odorous water bodies, etc. These issues are assessed before selecting the LID facilities that can be used.

[0045] Considering the requirements of older residential communities for runoff control, pollutant reduction, LID facility construction costs, post-construction maintenance, and site conditions, but also recognizing that sponge city transformation of older communities is difficult to meet with high construction and maintenance costs, and that the limited space available for green facilities in most communities makes it impossible to construct LID facilities with large site requirements, and that the primary need of older residential communities is generally to control rainwater runoff to reduce urban flooding caused by rainfall, LID facilities with better runoff control effects are initially selected. Based on the characteristics of LID facilities in the "Technical Guidelines for Sponge City Construction—Construction of Low Impact Development Rainwater Systems (Trial)" and the above requirements, the initial LID facilities selected for sponge city transformation of residential communities include green roofs, rainwater bins, rain gardens, and permeable paving. The maximum proportion of selected facilities needs to be adjusted according to the specific circumstances of different communities, increasing or decreasing the thresholds for different requirements to achieve the best results.

[0046] 1) Permeable pavement. Permeable pavement can increase infiltration and reduce surface runoff. Since traffic roads are more polluted than ordinary roads, grassed swales can be set on one or both sides at a certain slope ratio. In this way, the pollutants carried away by rainwater can be purified to a certain extent by the vegetation after being washed away by rainwater. It also has a certain aesthetic value and increases the happiness of residents.

[0047] 2) Green roofs. To reduce the accumulation of roof runoff and surface runoff, roofs are converted into green roofs, and rainwater collected on the roof is diverted into rainwater tanks. Rainwater purified by green roofs has a lower pollutant content and can be reused after certain treatments, or discharged into rainwater pipes after a certain period of time, thereby reducing and delaying runoff peaks.

[0048] 3) Rain gardens. Rain gardens are effective in controlling runoff and can be integrated with landscaping. Rainwater collected from permeable pavers, grassed swales, and green roofs can be channeled into rain gardens for retention, absorption, and purification, thereby delaying runoff peaks and reducing pollution.

[0049] Step 2: Setting the objective function and constraints.

[0050] Choice of objective function

[0051] The main problem in the community is severe flooding during periods of continuous rainfall, coupled with prolonged drainage times, which causes significant inconvenience to residents and poses certain safety hazards and property damage. However, cost is an unavoidable issue for the community. Therefore, the objective function for the community's LID (Land of Isolation) facilities primarily considers both stormwater runoff reduction and cost-effectiveness.

[0052] Objective function for stormwater runoff reduction rate:

[0053] ;

[0054] in, This represents the installation area of ​​the i-th type of LID facility. This refers to the sum of the areas within the community that are to be renovated. The runoff coefficient of all areas to be upgraded that require the installation of the i-th type of LID facility before the upgrade. To lay out an area of ​​[area] in all areas to be upgraded where the i-th type of LID facility needs to be installed. The runoff coefficients after the i-th type of LID facility are shown in Table 2.

[0055] Table 2

[0056]

[0057] LID Facility Annual Cost Function

[0058] ;

[0059] Where i represents the i-th type of LID facility; — Area of ​​the i-th type of LID facility (m²) 2 ); —Unit price of the i-th type of LID facility (yuan / m) 2 ).

[0060] The unit price range for some LID facilities is shown in Table 3 below.

[0061] Table 3

[0062]

[0063] Constraints

[0064] Each LID facility sets its own upper limit based on the actual measured area;

[0065] ;

[0066] Let be the minimum installation area of ​​the i-th type of LID facility. In this embodiment, the maximum installation area of ​​the i-th type of LID facility is given. It is 0.

[0067] Set the installation area of ​​the i-th type of LID facility. Maximum and minimum values.

[0068] This embodiment focuses on the usable area for rain gardens, green roofs, and permeable paving, etc.

[0069] Rain gardens: The entire existing green space is transformed into the maximum usable area for rain garden facilities;

[0070] Permeable pavement: Permeable pavement is generally used for hardened ground areas such as roads, parking lots, and activity areas, and is the maximum usable area to be transformed into different types of permeable pavement.

[0071] Green roofs: The maximum usable area of ​​office / commercial area roofs and residential building roofs that can be converted into green roofs;

[0072] The design scale of rain gardens, sunken green spaces, and permeable pavements should meet the following constraints:

[0073] ;

[0074] ;

[0075] in, This refers to the area of ​​green space within the residential community. The area to be paved for sunken green spaces. The area covered for the rain garden; For the area of ​​permeable pavement, Area of ​​roads within the residential community.

[0076] Step 3: Optimize methods and processes.

[0077] First, an iterative multi-objective optimization algorithm is constructed. After multiple iterations of "exhaustive search + Euclidean distance," the optimal solution for determining the location of LID (Limited Area Identifier) ​​combinations is obtained. Then, innovatively, "exhaustive search + Euclidean distance" is combined with iterative loops to calculate the specific location of the LID facilities.

[0078] The following is the specific optimization process:

[0079] Step 1: Iterate using the stormwater runoff reduction rate as the first objective function.

[0080] First, the stormwater runoff rate without LID (Light Identification and Discharge) facilities is calculated for comparison. Then, using stormwater runoff reduction as the first objective function, multiple iterations are performed. First, it is determined whether the preliminary conditions for constructing green roofs and rain gardens are met, and a screening process is conducted. For green roofs: the roof slope is determined; if the roof slope is greater than 15°, green roof construction is not allowed; if it is less than 15°, construction is permitted. For rain gardens: it is determined whether there are any convertible green spaces within the community; if so, rain gardens can be constructed; otherwise, they are not.

[0081] Using the minimum setting ratio of each LID (Light Influenced Device) in the stormwater runoff reduction objective function as the starting point for iteration and the maximum setting ratio as the upper limit, the areas of LID facilities such as green roofs, permeable paving, rain gardens, and sunken green spaces are set arithmetically with a tolerance of 1%. During calculation, the individual LID facility, such as a green roof, is calculated first, and the actual area of ​​the green roof is substituted into the formula from the minimum ratio to the maximum ratio. The stormwater runoff reduction rate is obtained from the first step; then, the stormwater runoff reduction rate of other LID measures is calculated separately. Finally, the integrated LID facility is calculated by substituting the actual area of ​​green roofs into the formula in increments of 1%, from the lowest to the highest percentage. The calculation is performed to obtain its stormwater runoff reduction rate, and then the actual area of ​​the permeable pavement is substituted into the formula from the lowest to the highest proportion. In the process, the stormwater runoff reduction rate is calculated until the highest setting ratio of the last LID facility is added, which is the final calculation result of runoff reduction.

[0082] The specific iterative process of LID facilities with stormwater runoff reduction as the objective function is as follows: Assume that the first LID facility is substituted into the formula for the first time. The starting value is its minimum setting ratio n%. The maximum settable area corresponding to the first LID facility is A1, and the minimum settable area corresponding to the first LID facility = A1 × n%. The ratio substituted in the second iteration is the ratio substituted in the first iteration plus 1%, i.e., (n + 1)%. The area value of the second iteration is A1 × (n + 1)%. The ratio value of each subsequent iteration is the ratio value of the previous iteration plus 1%, until the maximum setting ratio limit of the first LID facility, 100%, is reached. At this time, the maximum settable area of ​​the first LID facility is A1 × 100% = A 1. The iteration of the first LID facility ends. Next, the second LID facility is added. Assume the starting value of the second LID facility is its minimum setting ratio m%. The maximum settable area corresponding to one LID facility is A2. The minimum settable area corresponding to the second LID facility = A2 × m%. In each subsequent iteration, the value substituted is the previous iteration's value plus 1%, i.e., (m+1)%, corresponding to an area of ​​A2 × (m+1)%, until the maximum setting ratio of the second LID facility, 100%, is reached. At this point, the corresponding area is A2 × 100% = A2. When adding the second facility in an iteration, starting from the minimum setting ratio of the first facility, each ratio value of the second facility is calculated once. That is, when the ratio of the first facility is n%, the second facility is calculated once from m% to its maximum ratio of 100%; when the ratio of the first facility is (n+1)%, the second facility is calculated once from m% to its maximum value of 100%, and so on, until the maximum ratio of the first facility, 100%, is reached, at which point the iteration of the second facility ends. The same calculation steps are performed when adding the third LID facility, continuing until the maximum setting ratio of the last LID facility is added, at which point the overall iteration ends. After the iteration is complete, the results obtained from the iteration will be... The values ​​are sorted from smallest to largest, and the maximum value is output, along with the proportion and area value of each LID facility corresponding to the maximum value.

[0083] Step 2: Iterate using the annual cost of LID facilities as the second objective function.

[0084] Substitute the calculated stormwater runoff reduction rate combination schemes into formula (2). The cost calculation formula includes the calculation of the annual cost of LID facilities. According to... and The calculation results are sorted, and each one is selected. The corresponding minimum .Will Consider it as the x-axis. Considering it as the y-axis, let p and q be two points on it: p f1 >q f1 , and p f2f2 If p is retained, then p is retained. p f1 ≥q f1 , and p f2 f2 If p is retained, then p is retained. p f1 >q f1 , and p f2 ≤q f2 If p is not found, then p is retained. The overall iteration ends.

[0085] After the iteration, LID facility combination schemes with rainwater runoff reduction rates of 30%, 40%, and 50% (or other ratio combinations, determined according to the specific needs of different study areas) were selected and substituted into the SWMM model to analyze the operation results.

[0086] Meanwhile, since different communities have different situations, a more suitable combination of LID facilities can be selected according to different situations. For example, if community A has poor drainage capacity after rainfall and is prone to water accumulation, but the community environment is good and there are few black and smelly water bodies in the past, then the community can increase the proportion of LID facilities with strong drainage and infiltration capacity, such as permeable pavement, and appropriately reduce the proportion of LID facilities with good pollutant reduction capacity, such as rain gardens.

[0087] Considering the construction age and space limitations of some communities, the greening rate is low or even almost non-existent, and the area available for renovation is very limited. Therefore, it is necessary to increase the upper limit of the proportion of permeable pavement. Where the roof conditions are suitable, the upper limit of the proportion of green roof should also be increased. Furthermore, when the community conditions are suitable, it is advisable to use regulating facilities that occupy less ground space, such as infiltration wells, rainwater tanks, and water storage ponds, to mitigate waterlogging and control rainwater runoff.

[0088] The optimal solution for determining the location using "exhaustive search + Euclidean distance" combination of LIDs is found.

[0089] ​​First, using an exhaustive method, list all possible combinations of facilities within the sub-catchment area that need renovation. For example, if the theoretical optimization value for green roofs is 70%, and there are 7 roofs in the sub-catchment area that can be renovated, then any 4-6 roofs can be selected for combination and proportion calculation. If the closest result is within ±5%, it is retained (or within another proportion range); otherwise, it is left undetermined and calculated in the next iteration. Similarly, calculate the proportion range of rain gardens and permeable paving that is closest to the theoretically optimized LID area. Then, calculate the Euclidean distance to obtain the minimum Euclidean distance between the three, which is the optimal actual facility area. At this point, the minimum difference between the actual facility area and the theoretically optimized LID area is obtained, and the specific buildings and facilities that need renovation within the area can be determined. Repeat the above steps, fixing the area proportion of each LID facility in the sub-catchment area one by one, until the optimal area proportion of all LID facilities is close to the actual area proportion.

[0090] ;

[0091] In the formula: For ideal values ​​of green roofs, This represents the actual value for green roofs; For rain gardens, This represents the actual value for the rain garden; For permeable pavement, the ideal value is... This represents the actual value for permeable pavement.

[0092] SWMM model simulation verification

[0093] This implementation used P=2, 5, 10, and 20a as input data for the SWMM model, respectively, to obtain simulation results of the annual runoff volume control rate under the scenario of no LID facilities after development in the study area and under different selected LID facility combinations. p is the return period (symbol P), which is a statistical indicator that measures the rarity of extreme events.

[0094] Catchment generalization

[0095] Based on different land use functions, the study area is divided into three zones: residential area, green area, and commercial / office area. The catchment area is further divided by considering the topography, land use planning, building and street distribution, pipeline network layout, and the current drainage zoning of the stormwater drainage network. When a single residential area is used as the study area, the functional zones are relatively simple, and the topography changes are minimal. In this case, the actual pipeline network layout and satellite imagery can be used as a background when drawing the catchment area.

[0096] Rainwater pipe network generalization

[0097] Simplify appropriately based on actual conditions, retain pipes that directly affect drainage results, and determine the outlet and water flow direction in the pipe network.

[0098] Model parameter settings

[0099] The parameters for the hydrology module of the model were set with reference to the SWMM model user manual and in conjunction with literature review. Specifically, the Horton infiltration equation was used for the infiltration model, and the specific parameter settings are shown in Table 4. The hydraulics module of the model adopted a dynamic wave-based pipe network confluence model, and the material of the drainage trunk line and its Manning coefficient were determined based on actual conditions. Considering the actual situation of the community and the renovation goals, three LID (Living Indoors) facilities—green roof permeable paving, rain gardens, and more—were selected as sponge city optimization measures for the community. Referring to the guidelines, the parameters for the LID facilities in the SWMM model were determined, as shown in Table 5.

[0100] Table 4

[0101]

[0102] Table 5

[0103]

[0104] Model rainfall sequence selection

[0105] The simulated rainfall events used the Chicago rainfall pattern. The storm intensity formula for the city in the study area was used, with return periods of P=2, 5, 10, and 20 years, and a short duration of 120 minutes for the storm duration. The peak rainfall coefficient r was generally selected from 0.3 to 0.5 based on the actual situation (generally 0.4 when actual peak rainfall location data is lacking). The rainfall process lines under different return periods were obtained by simulating two types of rainfall: rainfall with different return periods and actual annual rainfall.

[0106] Taking an old residential community in Yangzhou as an example, the results of different combinations of LID facilities after iterative optimization were substituted into the SWMM model.

[0107] Yangzhou City is located in central Jiangsu Province, with a subtropical monsoon climate. The average annual rainfall is 800-1200 mm, but the distribution of rainfall is extremely uneven, with summer and autumn accounting for 60%-80% of the annual precipitation. The study area covers approximately 15.4 hectares. 2 Apart from the building exteriors, most of the area is a gray, impermeable zone with low surface permeability. The northwest, northeast, and southeast sides of the community are higher in elevation, while the lower elevations are mainly concentrated on the southwest and northeast sides. See details... Figure 2 The drainage system in the study area is a separate system, where rainwater is discharged into the drains through pipes. During heavy rainfall, rainwater collects in low-lying areas, causing flooding in a short period of time.

[0108] The LID facilities suitable for the community were selected as follows: green roof, permeable paving, and rain garden. The area of ​​different functional zones in the study area was calculated using ArcGIS software, and Table 6 was obtained based on the constraints.

[0109] Table 6

[0110]

[0111] Iterative calculations were performed on the three types of facilities using stormwater runoff reduction and cost formulas, resulting in 49 possible combinations. (See attached...) Figure 3 Based on the screening results, the optimal input-output ratio for stormwater runoff reduction is 37.15%, with an investment cost of 7.54 million yuan. This corresponds to green roofs, permeable paving, and rain gardens accounting for 9%, 54%, and 5% of the total area, respectively. The optimal proportions of these LID (Light Industry Development) facilities are then substituted into the SWMM (Survey-Simplified Model). The catchment area is generalized, as follows: Figure 4 The simplified diagram of the stormwater pipe network obtained from the SWMM model is shown below.

[0112] The 120-minute rainfall duration process lines under different return periods were calculated based on the formula for the intensity of heavy rainfall in Yangzhou City. These process lines are as follows: Figure 5 As shown, the formula for the intensity of rainstorms in Yangzhou is:

[0113] ;

[0114] Where: i—design rainfall intensity. [L / (hm 2 ·s)];

[0115] T – Design recurrence period (years);

[0116] t——Rainfall duration (min).

[0117] The annual runoff reduction rate simulated by the SWMM model for each return period without LID and under the optimal input-output scenario with LID facility area is shown in the figure. Figure 6 The results showed that the annual runoff volume control rate was 79.94% when P=2, and decreased to 73.02% when P=20, both meeting the requirements of the guidelines for annual runoff volume control rate. This indicates that the runoff reduction effect decreases with the increase of the return period.

[0118] After multiple cycles of LID facility deployment optimization, the changes in the LID layout and specific locations for each sub-catchment area under the three schemes are shown in [link to documentation]. Figure 7 The specific corresponding locations are shown in Table 7 below. Figure 7(a) in the diagram is a schematic diagram of Scheme 1, showing the green roof area in column 1 of Table 7, the rain garden area in column 2 of Table 7, and the permeable pavement area in column 3 of Table 7 in Scheme 1. Figure 7 (b) in the diagram is a schematic diagram of Scheme 2, showing the green roof in column 4 of Table 7, the rain garden in column 5 of Table 7, and the permeable paving in column 6 of Table 7. Figure 7 (c) in the diagram is a schematic diagram of Scheme 3, showing the green roof in column 7, area 7, the rain garden in column 8, area 7, and the permeable paving in column 9, area 7. It can be seen that the main change in the diagram is that the permeable paving in the south has been moved from the center to the west side. This is because the western side is geographically lower, making it prone to water accumulation after rainwater runoff, thus requiring more adjustment from LID (Light Injection Discharge) facilities to alleviate the water accumulation situation.

[0119] Table 7

[0120]

[0121]

[0122] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A design method for sponge city transformation of residential communities that balances construction costs and runoff reduction, characterized in that, Specifically, According to the characteristics of the community and the region to be transformed, appropriate LID facilities are selected for the region to be transformed in the community; The theoretical optimal laying area of each LID facility is calculated by setting a constraint condition to maximize the total rainwater runoff reduction rate and minimize the cost; Based on the theoretical optimal laying area of the i-th LID facility, the i-th LID facility is laid in the appropriate region among all regions requiring the i-th LID facility.

2. The method for design of a field reformation for sponge according to claim 1, wherein, The expression of the total rainwater runoff reduction rate is as follows: ； wherein, represents the laying area of the i-th LID facility, is the sum of the areas of the to-be-renovated regions in the cell, is the runoff coefficient of all the to-be-renovated regions needing to lay the i-th LID facility before renovation, is the runoff coefficient after laying the i-th LID facility with an area of in all the to-be-renovated regions needing to lay the i-th LID facility.

3. The method for designing a cost-effective and runoff-reducing retrofit of a site for infiltration according to claim 1, wherein, The constraint condition is specifically: maximum and minimum values of the laying area of the i-th LID facility are set If the selected LID facilities include rain gardens and permeable pavements, the following constraint condition is set: ； ； wherein, is the area of green space within the cell, is the area of depressed green space laid, is the area of rain garden laid; is the area of permeable pavement laid, is the area of road within the cell.

4. The method for designing a cost-effective and runoff-reducing retrofit of a site for infiltration according to claim 1, wherein, When calculating the theoretical optimal laying area of each LID facility, the area value scheme of the i-th LID facility is set: For the i-th LID facility, set its initial value as , and set the area value scheme of the i-th LID facility in proportion to : , , , , .

5. A design method for cost-effective and runoff-reducing retrofit of a small cell according to any one of claims 1 or 4, characterized in that, The calculation of the theoretical optimal laying area of each LID facility is specifically as follows: for the first LID facility, the total rainwater runoff reduction rate and the cost under all area value schemes of the first LID facility are calculated, each area value scheme of the first LID facility is combined with all area value schemes of the second LID facility, and the total rainwater runoff reduction rate and the cost are calculated again, and the iteration is performed in turn until the last LID facility is added, to obtain the total rainwater runoff reduction rate and the cost under all combinations, and according to the actual situation, the optimal combination is selected as the target of maximizing the total rainwater runoff reduction rate and minimizing the cost.

6. The method for designing a cost-effective and runoff-reducing retrofit of a site for infiltration according to claim 1, wherein, The i-th LID facility is laid in the appropriate region among all regions requiring the i-th LID facility, specifically based on the regions requiring the i-th LID facility, a plurality of regions are selected and combined multiple times, so that the difference between the sum of the areas of the plurality of regions and the theoretical optimal laying area of the i-th LID facility is less than a preset value, and multiple combinations are obtained for the i-th LID facility, and the optimal combination is selected from the multiple combinations.

7. The method for designing a cost-effective and runoff-reducing retrofit of a site for infiltration according to claim 6, wherein, The optimal combination is selected according to the following formula: ； wherein, is the Euclidean distance, is the theoretical optimal laying area of the i-th LID facility, is the actual laying area under the combination of a plurality of regions corresponding to the i-th LID facility, and I is the total number of LID facilities. selecting The smallest combination as the optimal combination.

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