The challenge posed by urbanization often revolves around effectively integrating land use and comprehensive drainage planning. The empirical results of urban layout on stormwater management are summarized into two major categories: (1) decrease of runoff volume and (2) decrease of peak flows. Interdisciplinary incorporation of urban design and hydraulic engineering should be employed for reducing upstream runoff volumes and a regional downstream detention system to mitigate peak flow releases. This study proposes a framework that combines the distribution of flow loading and the control of flow releases to formulate the adaptation strategy by synthesizing land use and comprehensive drainage planning. The study leverages environmental and land use data to investigate Dapu township, Taiwan. The presented paper designs a detention and low-impact development (LID) method based on relative land use layout. It identifies the relationships between land use and master drainage planning (MDP) in watershed areas. It contributes to an integrated framework for the urban planners' flood mitigation adaptation strategy. Most importantly, it provides insights into MDP practices under slight, medium, and even climate change scenarios.

  • The novel integrated land use and comprehensive drainage planning to create a unique framework is explained.

  • Provides insights into MDP practices under climate change scenarios.

  • A novel runoff volume-based method for MDP was developed.

  • Provides urban planners with an integrated framework that is easy to use.

In the past few decades, the impact of urbanization on watershed hydrology has been investigated, and the increase in urban storm runoff is directly proportional to the impervious area in the watershed (Parkinson 2003; Shuster et al. 2005; Dietz & Clausen 2008; Qin et al. 2013; Liu et al. 2015; Leimgruber et al. 2018; Bai et al. 2019; Feng et al. 2020; Andualem et al. 2023). Flood wave movements become more concentrated after replacing the natural drainage network with man-made streets and sewers (Guo 2003). The runoff volumes and peak flows increase because soil infiltration is significantly reduced due to more pavements (Elliott & Trowsdale 2007). To mitigate the negative impacts of developments on the urban water environment, urban planners need to conduct a regional master drainage plan in which the future land use plan can include an effective stormwater drainage system to mitigate potential flooding problems from extreme storm events (Brabec et al. 2002).

The above descriptions address a significant problem not only globally but also locally. An island country, Taiwan issue, located in East Asia, is threatened by flash floods (Chang et al. 2021; Guo et al. 2023) and needs to formulate a suitable method to prevent urban flooding. The overloading concept in stormwater management has two strategies: First, the distribution of flow loading according to watershed area size should be controlled downstream at the junction, and the excessive runoff should be allocated to avoid flood disasters (Guo & MacKenzie 2014); second, the control of flow releases expecting to recover the function of water resource retention, to increase permeation, and to reduce runoff, water conservation areas like depressions and natural lakes were constructed (Emerson et al. 2005). The previous studies aimed to determine available master drainage planning (MDP) in cities. Conventional studies that aim to solve the on-site drainage system associated with a small sub-area are often designed using the rational method. The network of MDP is organized according to three major process categories: (1) river-based MDP, (2) city-based MDP, and (3) site-based MDP. These categories represent impervious area, peak flow, infiltration, and runoff volume processes or mechanisms.

A regional MDP consists of three elements, including I-design using LID devices at the upstream points of runoff sources and Q-design using streets-sewers-ditches to collect and convey runoff flows to the watershed outlet effectively. At the outfall point, V-design uses wetland, retention, and detention facilities to reduce the release of flows into the downstream receiving water bodies. An MDP provides an overall assessment of various alternatives to use the combinations of I-, Q-, and V-designs to lay out LID devices upstream, drainage systems through the watershed, and detention systems downstream. The alternative studies aim to minimize the costs and maximize public safety.

Taiwan faces an extremely high risk of flood disasters due to abundant rainfall. Moreover, with a dense urban population, numerous flood control projects have been constructed. Building large-scale flood control projects has become challenging given the current land use patterns. Therefore, utilizing LID in conjunction with micro-detention effectively reduces peak discharge and decreases the area and depth of flooding. This study aims to provide an adaptation strategy based on the distribution of flow loading and control of flow releases approach of watershed-integrated stormwater management. A disaster hotspot, the Dapu area, located in Chiayi County, Taiwan, is adopted as the research area. Firstly, hydrological practical and land use development processes are considered. Then, the StormWater Management Model (SWMM) is embedded to simulate the runoff flow in the Dapu area. Under the above framework, three sets of plan methods are separately produced for (1) river-based MDP, (2) city-based MDP, and (3) site-based MDP. Finally, a reliable result can be suggested as an improved decision-making approach. MDP will provide a quantifiable basis to develop future management plans on land uses and infrastructures for stormwater and transportation systems under different precipitation scenarios (slight, medium, and climate change). In conclusion, the highlight of this study is to integrate a framework for urban design and hydraulic engineering and provide a practical approach to MDP.

Level of MDP

Any jurisdictional and political boundaries do not bind storm and storm runoff. Therefore, a river basin could be an overall drainage planning unit, as shown in Figure 1. A river collects inflows as it flows downstream. Design points along a river are placed where the design flow is changed due to the inflows coming from lateral branches. The computational efficiency demands a large-scale approach to model a large, complicated river basin. As a result, the numerical discretization on the mesh network is usually at a low resolution. Therefore, a city is represented as a point in a river basin model. The primary purpose of MDP for a river basin is to establish a safe capacity through the river. All levees and banks are designed to safely deliver the design flows for the pre-selected level of risk. At the outfall point of a waterfront city, the MDP for the river basin will define the maximum allowable flow release from the city. In case the town is overdeveloped and would release higher peak flows than the allowable defined in the river basin MDP, a mitigation plan such as flood detention must be implanted at the outfall point so that the flow released from the city into the river will never cause an overload to the river.
Figure 1

Network of different levels of master drainage plans.

Figure 1

Network of different levels of master drainage plans.

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Similarly, an MDP must be developed for each city. The city's significant drainage method should be treated like a river. At all design points on the drainage route, the design flows should have been defined by the city-based MDP. In case any site has been overdeveloped, the outfall point of the site needs a mitigation plan to reduce the flow release to stay within the allowable release. A site should have a small-scale, detailed MDP that defines the flow path, location of low-impact devices, etc. The MDP network is integrated with multiple levels of details, including at least three levels: (1) river-based MDP, (2) city-based MDP, and (3) site-based MDP. An overall effectiveness of MDP is the enforcement of MDP from all individual sites, cities, and the entire river basin. All levels of MDPs define the design flows at all design points. These design flows set the level of safety as to whether we need a detention basin for runoff flow reduction and porous low-impact designs for runoff volume reduction. As a rule of thumb, a river-based MPD can be numerically modeled using the kinematic wave approach without consideration of backwater effects (Guo et al. 2012). A city-based MPD shall consider the backwater effect of the river. Therefore, a dynamic approach is preferred. For a site-based MPD, the construction plans shall provide detailed flow paths and the location of low-impact facilities such as porous pavers, gardens, infiltration beds, etc.

Stages in watershed development

The hydrologic changes in watershed development are illustrated in Figure 2. A natural drainage network comprises the overland flows in the upland areas, swale flows when the overland flows become concentrated due to surface erosion, and river flow when the flow cross-section is well defined.
Figure 2

Comparison between natural and urban watersheds.

Figure 2

Comparison between natural and urban watersheds.

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After developments, the natural waterway is replaced with the significant sewer trunk line along a collector street, while the incoming creeks are replaced with the branch sewer lines. Urban overland flows are generated from adjacent paved areas along a street. Most of the natural depressed regions and lakes are filled or leveled. Of course, most of the previous surface areas are converted into impervious areas such as roofs, parking lots, streets, etc. As aforementioned, the mitigation plan for increased stormwater includes LID devices as a replacement for natural depression and a regional detention basin as a replacement for raw storage such as pools and lakes.

It is critical to understand the stages in watershed development as illustrated in Figure 3, and the progress of the urban area might be divided into stages A to D. Stage A has inadequate infrastructure for stormwater drainage, and the surface runoff is driven by gravity all over the area. Technically speaking, it is a typical condition at the beginning of an urban setting. Stage B shows that streets and sewers are built as a conveyance system for effectively removing stormwater from the neighborhood areas. At this stage, public safety against flood waters dominates the concept of urban drainage. Stage C implies that a conveyance system is improved with a flood detention system at the outfall point for peak flow reduction. Stage C is the typical urban setting with the awareness of legal responsibility – resisting the upstream flood damage to the downstream properties. It is a classic urban stormwater management system from 1970 to 1990 in the US's metro cities. Stage D is more advanced to apply the LID concept at the upstream street corner for runoff volume reduction and a detention basin at the downstream outfall point for peak flow reduction. After 2000, stormwater management must include how to cope with frequent events (3- to 6-month rainfall events) for runoff volume reduction and how to mitigate the extreme events (2- to 100-year storm events) for peak flow reduction in Taiwan. The above two scenarios are concerns of flood threats to public safety.
Figure 3

Stages of urban drainage system developed in urban areas.

Figure 3

Stages of urban drainage system developed in urban areas.

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Urban development is always staged and random in time and space. As illustrated in Figure 3, the continuous development from Stages A to D requires early land use planning to accommodate the spatial and temporal needs in the MDP. For instance, which streets should be selected to lay out the major sewer trunk lines, and where should land dedications for future LID or detention facilities be? All these details must be planned ahead of random urban development. For an urban renewal project, the old town may need more flexibility to accommodate the flooding problems. An MDP has to be developed with various alternatives to mitigate the flooding problems to an acceptable risk level.

Multiple land uses for multiple design events

The urban drainage system carries cascading flows from micro, minor, and major systems. An MDP is a spatial analysis used to optimize land use. For instance, how to select the best strategic location for a city park so that it remains open for recreation during dry days and is reserved for flow flood detention during wet days, how to use the available space along waterways as greenbelts, and how to convert floodplains into bike paths and waterfront parks.

The stormwater systems, composed of major, minor, and micro facilities, are critical, as shown in Table 1. A microsystem is designed to intercept the 3- to 6-month frequent events for water quality enhancement. Examples of micro facilities are LID devices, including rain gardens, infiltration beds, porous pavers, etc. When the microsystem is overtopped, the excess water flows into the downstream minor system, which includes street inlets, underground sewers, roadside ditches, etc. A little system is designed to pass the 5- to 10-year events. After the minor system becomes full, water will overflow into the significant systems, such as street gutters, flood channels, natural waterways, etc. All primary drainage routes must be capable of passing the 50- to 100-year events. The application method will be presented in the following chapter.

Table 1

Integration of river basin plan and city drainage plans

PurposeDesignsFacilities
Filtering LID I-design (micro) Infiltration basin, porous pavers 
Conveyance Flow Q-design (minor/major) Streets, sewers, channels, 
Storage Storage V-design (major) Detention, retention, wetland areas 
PurposeDesignsFacilities
Filtering LID I-design (micro) Infiltration basin, porous pavers 
Conveyance Flow Q-design (minor/major) Streets, sewers, channels, 
Storage Storage V-design (major) Detention, retention, wetland areas 

The hydrologic impact of urbanization is an integration of watershed hydrologic cycles and human activities (Sheng & Wilson 2009). Most studies on urban watersheds have addressed various methodologies to simulate urban stormwater generation and movements (Galster et al. 2006). Still, the fundamental concern is how to conduct RDMP (regional drainage master planning) to quantify the hydrologic changes in watershed regimes. In practice, an RDMP is performed using computer numerical simulation. The most popular computer models are the US EPA SWMM5 and US COE HMS (Huber et al. 2005; Chu & Steinman 2009). The input parameters include design rainfall information, watershed hydrologic parameters, street and sewer network, and hydraulic features, including culverts, LID devices, detention basins, etc. In practice, the existing watershed model should be developed to reflect the current condition, while the future watershed model should be designed according to the future fully expanded condition. To evaluate the impact of a specific development project, the pre-and post-development models must be developed to identify the changes with and without the proposed project. A mitigation plan for the changes should be developed using alternative models to minimize the cost and maximize the level of safety. Various alternatives can be created with different combinations of drainage features.

Land use model for effective imperviousness

A LID drainage design is flow path dependent. The four-component land use model in Figure 4 consists of three draining flow paths. This land use model is divided into four drainage types: DCIA refers to the directly connected impervious area draining to the street; UIA refers to the unconnected impervious area; RPA refers to the draining to the receiving pervious area, and SPA refers to separate pervious area draining to the street. As illustrated in the example, East Roof is a CIA that directly drains into the street. The west roof is a UIA that drains onto the grass area as an RPA. The porous driveway is directly connected to the street as a SPA. The application of this land use model is to minimize the effective imperviousness at every building site (Bhandari et al. 2015).
Figure 4

On-site land use layout.

Figure 4

On-site land use layout.

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The total tributary area for the site is as follows (Guo 2010):
formula
(1)
formula
(2)
formula
(3)
where indicates the total site area; AUIA indicates the area for unconnected impervious area; ARPA indicates the area of receiving pervious area;  ACIA indicates the area for DCIA; ASPA indicates the separate last area, and using the area-weighted method, the lumped model for the site would have an imperviousness ratio as (Han & Burian 2009):
formula
(4)
Equation (4) ignores the additional infiltration loss over the cascading plane. As a result, Equation (3) needs to evaluate the effectiveness of an LID design and provide incentives to encourage stormwater best management practices (BMPs). The cascading plane consists of ARPA. The area-weighted imperviousness ratio for the cascading plane is:
formula
(5)
The effective imperviousness ratio is derived for the cascading plane using the reduction factor:
formula
(6)
where indicates the effective imperviousness for cascading plane. Incorporating Equation (6) into the lumped model for the entire site, the site's effective imperviousness is:
formula
(7)

Taiwan is a small island in the South China Sea, spanning 36,000 km2. Despite its size, the island has high mountains that reach peaks of 2,000–4,000 m, running through its center. Due to the island's geological and climate conditions, it experiences frequent and significant natural disasters, such as earthquakes, landslides, and floods caused by typhoons. This study focused on the Dapu township, situated upstream of Tsengwen Reservoir, and examined its MDP levels. The Tsengwen River basin is a crucial reservoir water source, the sole water provider for the southwest region of Taiwan. This area has a population of approximately 2.67 million people. The terrain in the Dapuurban planning area slopes generally from east to west, with ground elevations ranging from 230 to 410 m. The average slope is 3.47% west and 37% east. The minimum temperature in January is about 16.16 °C, while the maximum temperature in July and August is 35.42 °C.

This study adopted the Matou Shan rainfall station situated at an elevation of 1,020 m in the Tsengwen Reservoir catchment area. According to the statistics from 1969 to 2022, the mean annual rainfall at Matou Shan is 2,817 mm; the maximum annual rainfall is 5,046 mm. The catchment area experiences a dry season between October and April each year. It has been observed that the precipitation in winter has a slight impact on the catchment area. Heavy rainfall, with more than 100 mm of daily rainfall to the Tsengwen Reservoir catchment, is often observed in the summer. The average rainfall varies monthly, with the highest in August, July, and June. The maximum daily reached 695 mm, and the 3-day maximum rainfall was 1,352 mm. The Dapu Township Urban Plan aims to achieve its target year of 2015. The plan includes a land use zoning plan that projects a population of 10,000 and a residential density of 220 people per hectare (ha). The project area covers a total of 203.67 ha.

The tributary area to the Tsengwen River has been developed into several small mountain towns that have caused tremendous increases in runoff flows and vast amounts of landslides and bank erosion upstream of the river. The deterioration of the Tsengwen River directly impacts the Tsengwen Reservoir. Tsengwen River must be preserved with its design flows because all bank protections and drop structures along the river were built according to the design flows stated in its MDP.

In this case study, the small town of Dapu, as shown in Figure 5, is chosen as an example to demonstrate how to integrate three levels of MDP to mitigate the increase of runoff flows and volumes. The town of Dapu has a total drainage area of 24.55 (ha). The average slope along the significant drainage route is 12.7%. The imperviousness as of the year 2015 is 25.7%. Drainage is a sewerage system using a diversion system. Storm Sewer Horner Design Parameters . The ditch type is a U-shaped ditch with a cover for side ditches, reinforced concrete pipe rectangular box culvert, or slurry trapezoidal open ditch for trunk and feeder routes. The length of side ditches is about 33.87 km, and the length of drainage trunks and branches is about 4.90 kilometers, except for some side ditches due to planned roads.
Figure 5

Location of the existing and after-development land uses.

Figure 5

Location of the existing and after-development land uses.

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Proper land use planning is imperative during Stage D. The paper highlights the connection between land use and MDP in watershed regions. It also proposes adopting the LID approach at the upstream street corner to minimize runoff volume and implementing a detention basin at the downstream outfall point to decrease peak flow. This holistic strategy can aid urban planners in effectively mitigating floods. Moreover, the paper offers valuable perspectives on MDP practices.

Design rainfall depths and distribution

We analyzed 25 years of hourly rainfall data from Station H1M250 in the City of Dapu, Chiayi County. From this analysis, we developed a 24-hour design rainfall distribution curve for a small event drawn as a purple line, as shown in Figure 6. The minor event could be a regular scenario and rarely produce disaster risk. We then used the purple curve to generate design rainfall curves for 2- (slight), 10- (medium), and 100-year (climate change) 24-h precipitation depths to be the boundary conditions, which are shown in Figure 6.
Figure 6

24-h design rainfall distributions at Dapu.

Figure 6

24-h design rainfall distributions at Dapu.

Close modal

It has been determined that the H1M250 station's proximity to the local climate and rainfall pattern is significant, so a chosen set of rainfall data from several representative areas in Taiwan's City of Dapu was analyzed. The data was collected from the Water Resources Agency and spanned an average of 25 years. A line chart displayed the cumulative distribution of rainfall events from small events to 100-year events over 48 h. The distribution was found to be expected. The statistics and parameters for high peak flow were also analyzed, including 100 years = 141 m3/s, 10 years = 76.4 m3/s, 2 years = 61.7 m3/s, and small event = 12.3 m3/s.

River-based MDP

The Tsengwen River is an important waterway that flows through Alishan Mountain and eventually empties into the Tsengwen Reservoir. The framework demonstrates that V-design uses retention and detention facilities to reduce the release of flows into the downstream receiving water bodies. To check the stagnant flood volume and flood capacity of the base drainage road at the development site, the outer water level will be used as the downstream water level boundary condition. The extreme water level record line can be calculated from the external drainage discharged into the regional drainage or the river at each recurrence of the flood level calculation or the outer drainage road known water level of the cross-section. According to the 2000 Taiwan River Database, the 100-year design flow rate at Dapu in the Tsengwen River is 15.8 m3/s. This means that the maximum amount of water that can be released from the Dapu area is 15.8 m3/s. As a result, this study aims to establish a Maximum Permissible Discharge (MPD) for Dapu, which ensures that the 100-year peak flow does not exceed 7.62 m3/s. To calculate the peak flow of each recurrence interval at the outflow of the development base, a one-dimensional hydrological calculation of the joint outflow into the regional drainage or the familiar outflow road at the river will be conducted. The calculation method of the peak flow of each recurrence interval of the familiar outflow road, the intercepting waterway, and the crossing waterway will be explained. This calculation will be used as the basis for verifying the flooding capacity of the watercourse and calculating the outer water level.

City-based MDP

The paper proposes an MDP that has three main parts. Firstly, it calculates the peak flow at each recurrence interval of the joint outfall, the interceptor, and the crossing. Secondly, it calculates the outer water level history. Finally, it calculates the discharge flow of the development base, ensuring that it does not affect the flooding capacity of the downstream joint outfall. When designing a microsystem to handle a 5- to 10-year return flood, it is essential to consider the pumping station's capacity, the downstream culvert section, and the availability of proper outlets for the drainage trunks simultaneously (Hsu et al. 2000; Cheng et al. 2015). However, due to the lack of measured flow data for storm sewer systems in Taiwan, only the depth of inundation is available, which makes it impossible to directly verify the accuracy of the design model incorporated into the design rainfall pattern, given that the SWMM model has been validated for the depth of inundation in many areas in Taiwan, its credibility is acceptable (Huang et al. 2018; Lin et al. 2021).

To determine the current condition through full development, MDP was used to analyze the basis for a regional plan for stormwater control in the watershed, summarized in Figure 7.
Figure 7

SWMM layout of existing watershed for land use status.

Figure 7

SWMM layout of existing watershed for land use status.

Close modal

Taiwan's Department of Water Resources (DWR) offers a simplified method to calculate the impervious surface ratio (IMP) for different land use zones. The study area's underlying surface was classified into greenspace, building, and road. Greenspace is considered a pervious surface, while buildings and roads are impervious. The imperviousness of each sub-catchment is calculated as the percentage of building and road areas: .

The Q-design uses streets, sewers, and ditches to collect and transfer runoff effectively to watershed outlets and at the outfall point. The effective collection and conveyance of runoff flows through streets, sewers, ditches, and canals converge to small flood storage ponds. These ponds are usually covered with concrete to store water, but they do not reduce the volume of water. Instead, they only change the drainage distribution over time, which means they only reduce the flow rate. When designing the roadway in urban planning land use detail plans, designers need to refer to the ‘Highway Drainage Design Guidelines’ to determine the scope of the study for the design of drainage facilities. Designers can then make appropriate decisions on the size of the drainage facilities, taking into account the risks and economics involved.

This study tributary area is 24.55 (ha) divided into seven subareas, as shown in Figure 8, of which an average of 25.7% is the impervious area. Here, a watershed is irregular in shape, and the KW (converging kinematic wave) approach requires conversion into the equivalent rectangle with a width LW and length XW, and . A watershed drains into its collector channel. The channel has a slope, indicates the vertical fall (elevation difference) and L indicates the channel length. After the shape conversion, the slope on the rectangle is . According to the energy conservation, .
Figure 8

Detention volume determined by hydrograph methods.

Figure 8

Detention volume determined by hydrograph methods.

Close modal

The average KW plane slope (Sw) for the study area is 4.3%, and the average width of the KW plane (LW) is 115.2 m. The infiltration rate for the sand mix used in this tributary area was reported to be 12.5–75 mm/h. The detailed hydrologic parameters are summarized, including pre-post watershed imperviousness, length, Sw, LW, and soil infiltration rates. Using the impervious percentage of 15%, the 100-year peak flow must be reduced from the post-development flow release of 7.62 to 3.78 m3/s. In this case, setting the control of flow releases to be the peak outflow under the pre-development condition, the after-detention hydrograph is approximated by a linear rising hydrograph (Guo 2006), as shown in Figure 8.

City-based MDPs are detention pond plans for predicting future watershed models that should be developed according to the future fully expanded condition (Figure 9). By holding a volume of stormwater runoff for an extended period of time, comprehensive detention control of flow releases can reduce peak flows.
Figure 9

SWMM model layout of post-development watershed for land use plan.

Figure 9

SWMM model layout of post-development watershed for land use plan.

Close modal

City-based MDPs were integrated to explain the peak flow reduction by detention ponds. The model determines detailed investigations by applying long-term runoff simulations to assess the needed stormwater quantity capture volume for a site, stormwater drainage system, municipality, or region. The control of flow releases analysis results reveal that the land use layout is linked with the drainage master plan. This method was improved using SWMM and GIS to determine the future development and road structures most closely associated with existing city-based detention ponds. This analysis primarily considers the economics of each detention facility since hydraulic facilities will cost more to infrastructure and occupy large tracts of land in the future.

According to the stage area storage for the proposed detention basin described in Table 2, the stage–storage curve is developed using triangular cross-sections. The 10-year and 100-year water depths in this basin under design are identified to be 1 and 3 m. The required stormwater detention volumes were 8,014 m3 for the 100-year event.

Table 2

Stage–area–storage for a proposed detention basin

DepthWater surface elevationBasin side slopeWidth of cross-sectionLength of cross-sectionCross-sectional pond areaAccumulated storageIdentify design water elevation
(m) m/m m sq m3/m2 sec  
0.0 244.00 4.00 25.00 30.00 750.00 0.0  
0.5 244.50 4.00 29.00 34.00 986.00 434.0  
1.0 245.00 4.00 33.00 38.00 1,254.00 994.0  
1.5 245.50 4.00 37.00 42.00 1,554.00 1,696.0 10-year 
2.0 246.00 4.00 41.00 46.00 1,886.00 2,556.0 100-year 
2.5 246.50 4.00 45.00 50.00 2,250.00 3,590.0  
3.0 247.00 4.00 49.00 54.00 2,646.00 4,814.0 Freeboard 
DepthWater surface elevationBasin side slopeWidth of cross-sectionLength of cross-sectionCross-sectional pond areaAccumulated storageIdentify design water elevation
(m) m/m m sq m3/m2 sec  
0.0 244.00 4.00 25.00 30.00 750.00 0.0  
0.5 244.50 4.00 29.00 34.00 986.00 434.0  
1.0 245.00 4.00 33.00 38.00 1,254.00 994.0  
1.5 245.50 4.00 37.00 42.00 1,554.00 1,696.0 10-year 
2.0 246.00 4.00 41.00 46.00 1,886.00 2,556.0 100-year 
2.5 246.50 4.00 45.00 50.00 2,250.00 3,590.0  
3.0 247.00 4.00 49.00 54.00 2,646.00 4,814.0 Freeboard 

The results of the flow releases from the study watershed are summarized in Figure 10 for the extreme events. The red line represents the 100-year peak flow under the post-development condition. The green line represents the control of the flow release curve under the pre-development condition. The 100-year peak flow must be reduced from the post-development flow release of 7.62 to 3.75 m3/s. The city detention can effectively mitigate the 100-year event, but they have no control over small events because all small flows are flowing through.
Figure 10

Stage-outflow for 100-year control of flow releases.

Figure 10

Stage-outflow for 100-year control of flow releases.

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Site-based MDP

In this study, the impervious outlet and pervious outlet sites are developed as shown in Figure 11, and are investigated. S11 will prioritize land acquisition in the future; based on the existing settlement area, two residential neighborhood units will be designated, with a total residential area of 3 ha. Based on the current catchment area and in line with the catchment scale, two residential neighborhood units with a total residential area of 3 ha will be designated. In the future, more land development and utilization are expected, which will increase the amount of runoff. To reduce or delay the peak flow of the development base, it is essential to consider the site conditions, drainage areas, and land use. Flood retention, flood storage, low-impact development (LID) facilities, increased surface infiltration, elevation management, or other outflow control facilities can manage the runoff.
Figure 11

Site-based MDP on S11.

Figure 11

Site-based MDP on S11.

Close modal

The primary purpose of the I-design is to enhance the quality of the water environment. It achieves this by improving the ability of runoff to infiltrate the ground surface in combination with an LID facility. This helps to prolong the time it takes for the runoff to collect and reduces the amount of pollutants that can contaminate the water supply through stormwater runoff.

The flow loading distribution represents the site's value to be developed with the micro facilities, including the LID devices, infiltration beds, and porous pavers. This paper modifies integrated land use and drainage planning; the two flow paths can be identified, as shown in Figure 11.

This case introduces a pervious outlet to drain the overland flow from the impervious area to the pervious area. In this case, setting the peak outflow to the peak outflow under the pre-development condition, the after-LID hydrograph is approximated by a straight line, which means that the LID devices are set to reduce the flow to enhance the water quality further.

Impervious outlet by site-based MDP

As discussed, many research studies have been conducted on the relationship between watershed imperviousness and the stormwater quantity and quality measured at the outfall point, according to Equations (4)–(6). A case study introduces the impervious outlet to drain the overland flow from the pervious area to the impervious area. The land use proposed for this lot consists of 70% of the lot, which is proposed to be family residences in this area, as shown in Figure 12. This case introduces an impervious outlet to drain the overland flow from the pervious area to the impervious area.
Figure 12

S11 for LID layout.

Figure 12

S11 for LID layout.

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The primary function of Type I-design is to improve the quality of the water environment, together with LID facilities to increase the capacity of runoff to infiltrate the surface, and to lengthen its collection time, in order to minimize pollutants from stormwater runoff to contaminate the water source, as shown in Figure 6. In terms of the base, the ordinances that specify the amount of rainwater storage or runoff from the building site, for example, the standard of the amount of runoff from the base of the development of the city of Taipei City that discharges into the sewers. The New Taipei City Urban Plan stipulates that rainwater storage and culvert water reuse related facilities should be set up to apply for the code of practice or the Central Statute – Architectural Technical Rules, Article 4-3, which are mainly for the purpose of disaster mitigation and flood prevention, and stipulates that the building base should be designed with the base amount to achieve the effect of disaster mitigation and flood prevention, and the Ministry of the Interior, Department of Construction, can refer to the ‘Low-impact Development Facilities in the Water Environment Operational Manual and Case Evaluation Plan’ as the reference for the future land use control. The Ministry of the Interior's Department of Construction's ‘Water Environment Low-Impact Development Facility Operation Manual and Case Evaluation Program’ can be a reference for future land use control.

Using the LID design and impervious outlet design as the basis on the o1 outlet, the 2-year peak flow must be reduced from the pre-development flow release of 0.27 to 0.22 m3/s, while the 2-year peak flow must be reduced runoff volume 4.81 m3/s. In this case, setting the peak outflow to be the peak outflow under the pre-development condition, the after-LID hydrograph is approximated by a linear, as shown in Figure 13. It meant the LID devices were set to reduce the flow for better water quality enhancement.
Figure 13

S11 LID volume determined by hydrograph methods.

Figure 13

S11 LID volume determined by hydrograph methods.

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Planning for land use and master drainage can be a highly effective way to adapt to flood control. Detention areas, like schools and parks, have been found to mitigate flood risks due to MDP. Stormwater management has become a significant concern in many cities, leading to an increased focus on the distribution of flow loading and control of flow releases. To determine the best placement of LID devices, this study has developed hydrological analytical techniques using SWMM-based analysis to create a land use layout. This paper aims for MDP to be developed for each city. At all design points on the drainage route, the design flows should have been defined by the City MDP. The network of MDP is integrated with multiple levels of details, including at least three levels: (1) river-based MDP, (2) city-based MDP, and (3) site-based MDP. This model described in this study reveals the differences in the hydrologic parameters in each tributary area. The results of the SWMM model simulate the effects of pre-development conditions on progressive stages in watershed development.

Previously, the MDP study only focused on flood flow calculations before and after site development without considering the relationship between land use and flood flow. This was achieved by estimating the flood flow based on the SCS uncalculated unit calendars. However, a new approach to MDP has been proposed, introducing a refined river, city, and site based on MDP. This new approach gives urban planners and water engineers a more comprehensive understanding of the relationship between land use and flood flow. It enables them to engage in a productive dialogue, facilitating better decision-making and more effective flood management strategies.

The river based on MDP considerations, uses wetlands, retention, and detention facilities to reduce the release of flows into downstream water bodies. An external water level record line is maintained from joint shallow drainage discharges into the regional drainage or river at intervals to check stagnant flood volume and the drainage road flood capacity of the downstream water level boundary conditions.

A city based on MDP considerations, the Q-design utilizes streets, sewers, and ditches to collect and convey runoff flows to the watershed outlet effectively. To ensure the flood capacity of the waterway and downstream water level boundary are within acceptable limits, it is necessary to calculate the flood peak flow for each recurring distance of the joint external drainage road, the intercepting waterway, and the traversing waterway. Q-design aims to improve the quality of the waterway.

The site based on MDP considerations and design aims to enhance the quality of the water environment. This is achieved through LID facilities, which help increase the capacity of runoff to infiltrate the surface. This, in turn, helps improve the water environment's overall quality. My design approach focuses on minimizing development's environmental impact and promoting sustainable practices.

Strategizing for land use and master drainage is a powerful means of adapting to flood control. Integrating detention areas such as schools and parks has proven effective in mitigating flood risks through MDP. Stormwater management has become a pressing issue in numerous cities, highlighting the need for increased focus on the distribution of flow loading and control of flow releases. To optimize the placement of LID devices, this research has devised hydrological analytical techniques utilizing SWMM-based analysis to generate a land use layout. This research employs a land use model and explores a runoff volume-based method that converts the effective imperviousness ratio into volume-weighted effective imperviousness and perviousness for two sequential plans. This approach is valuable in simulating impervious and pervious outlets for LID designs using an on-site MDP basis.

Financial support for this study was partially provided by a grant from the Ministry of Science and Technology (project number: 111-2625-M-035-007-MY3; 112-2625-M-033-001).

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

Andualem
T. G.
,
Peters
S.
,
Hewa
G. A.
,
Boland
J.
&
Myers
B. R.
2023
Spatiotemporal trends of urban-induced land use and land cover change and implications on catchment surface imperviousness
.
Applied Water Science
13
(
12
),
223
.
https://doi.org/10.1007/s13201-023-02029-7
.
Bai
Y.
,
Zhao
N.
,
Zhang
R.
&
Zeng
X.
2019
Storm water management of low impact development in urban areas based on SWMM
.
Water
11
(
1
).
Article 1. https://doi.org/10.3390/w11010033
.
Bhandari
A.
,
Monk
E.
&
Till
B.
2015
Review of the decision process for stormwater management in Western Australia
. In
36th Hydrology and Water Resources Symposium: The Art and Science of Water: The Art and Science of Water
, pp.
1300
1308
.
Brabec
E.
,
Schulte
S.
&
Richards
P. L.
2002
Impervious surfaces and water quality: A review of current literature and its implications for watershed planning
.
Journal of Planning Literature
16
(
4
),
499
514
.
Cheng
K. H.
,
Lin
C. H.
,
Chao
C.
,
Cheng
P. C.
&
Chen
Y. W.
2015
A study of equivalent manhole in streets-sewers of urban district instead of roadside water exchange by the SWMM model
.
Applied Mechanics and Materials
744–746
,
1045
1049
.
https://doi.org/10.4028/www.scientific.net/AMM.744-746.1045
.
Chu
X.
&
Steinman
A.
2009
Event and continuous hydrologic modeling with HEC-HMS
.
Journal of Irrigation and Drainage Engineering
135
(
1
),
119
124
.
Dietz
M. E.
&
Clausen
J. C.
2008
Stormwater runoff and export changes with development in a traditional and low impact subdivision
.
Journal of Environmental Management
87
(
4
),
560
566
.
Elliott
A. H.
&
Trowsdale
S. A.
2007
A review of models for low impact urban stormwater drainage
.
Environmental Modelling & Software
22
(
3
),
394
405
.
Emerson
C. H.
,
Welty
C.
&
Traver
R. G.
2005
Watershed-scale evaluation of a system of storm water detention basins
.
Journal of Hydrologic Engineering
10
(
3
),
237
242
.
Feng
M.
,
Jung
K.
,
Li
F.
,
Li
H.
&
Kim
J.-C.
2020
Evaluation of the main function of low impact development based on rainfall events
.
Water
12
(
8
).
Article 8. https://doi.org/10.3390/w12082231
.
Galster
J. C.
,
Pazzaglia
F. J.
,
Hargreaves
B. R.
,
Morris
D. P.
,
Peters
S. C.
&
Weisman
R. N.
2006
Effects of urbanization on watershed hydrology: the scaling of discharge with drainage area
.
Geology
34
(
9
),
713
716
.
Guo
J. C.
2003
Urban Storm Water Design
.
Water Resources. Publication
,
Littleton, CO
.
Guo
J. C.-Y.
2006
Urban Hydrology and Hydraulic Design
.
Water Resources. Publications
,
Littleton, CO
.
Guo
J. C.
&
MacKenzie
K.
2014
Modeling consistency for small and large watershed studies
.
Journal of Hydrologic Engineering
19
(
8
),
04014009
.
Guo
J. C.
,
Cheng
J. C.
&
Wright
L.
2012
Field test on conversion of natural watershed into kinematic wave rectangular plane
.
Journal of Hydrologic Engineering
17
(
8
),
944
951
.
Guo
W.-D.
,
Chen
W.-B.
&
Chang
C.-H.
2023
Error-correction-based data-driven models for multiple-hour-ahead river stage predictions: A case study of the upstream region of the Cho-Shui River, Taiwan
.
Journal of Hydrology: Regional Studies
47
,
101378
.
Han
W. S.
&
Burian
S. J.
2009
Determining effective impervious area for urban hydrologic modeling
.
Journal of Hydrologic Engineering
14
(
2
),
111
120
.
Hsu
M. H.
,
Chen
S. H.
&
Chang
T. J.
2000
Inundation simulation for urban drainage basin with storm sewer system
.
Journal of Hydrology
234
(
1
),
21
37
.
https://doi.org/10.1016/S0022-1694(00)00237-7
.
Huang
C.-L.
,
Hsu
N.-S.
,
Liu
H.-J.
&
Huang
Y.-H.
2018
Optimization of low impact development layout designs for megacity flood mitigation
.
Journal of Hydrology
564
,
542
558
.
https://doi.org/10.1016/j.jhydrol.2018.07.044
.
Huber
W. C.
,
Rossman
L. A.
&
Dickinson
R. E.
2005
EPA storm water management model, SWMM5
.
Watershed Models
338
,
359
.
Leimgruber
J.
,
Krebs
G.
,
Camhy
D.
&
Muschalla
D.
2018
Sensitivity of model-based water balance to Low impact development parameters
.
Water
10
(
12
).
Article 12. https://doi.org/10.3390/w10121838
.
Lin
J.-Y.
,
Yuan
T.-C.
&
Chen
C.-F.
2021
Water retention performance at Low-Impact Development (LID) field sites in Taipei
.
Taiwan. Sustainability
13
(
2
).
Article 2. https://doi.org/10.3390/su13020759
.
Liu
Y.
,
Ahiablame
L. M.
,
Bralts
V. F.
&
Engel
B. A.
2015
Enhancing a rainfall-runoff model to assess the impacts of BMPs and LID practices on storm runoff
.
Journal of Environmental Management
147
,
12
23
.
Parkinson
J.
2003
Drainage and stormwater management strategies for low-income urban communities
.
Environment and Urbanization
15
(
2
),
115
126
.
Shuster
W. D.
,
Bonta
J.
,
Thurston
H.
,
Warnemuende
E.
&
Smith
D. R.
2005
Impacts of impervious surface on watershed hydrology: A review
.
Urban Water Journal
2
(
4
),
263
275
.
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