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    城市建成区内涝风险评估及对策研究——以天津市南开区为例
    2019-07-19  点击:[]

    城市建成区内涝风险评估及对策研究——

    以天津市南开区为例

    Research on Evaluation and Countermeasures of Waterlogging Prevention and Cure in Urban Built-up Area—Taking Nankai District in Tianjin as an Example

    赵越 张斌* 王新亮

    ZHAO Yue, ZHANG Bin*, WANG Xinliang

     

    赵越 / / 1982年生 / 天津大学建筑学院城市规划与设计在读博士生 / 主要研究方向:应对洪涝灾害的城市空间规划

    ZHAO Yue, female, was born in 1982,Ph.D. students majoring in urban planning and designing, School of Architecture in Tianjin University. Major research direction: urban spatial planning for flood disasters.

    张斌* / / 1981年生 / 天津大学城市规划设计研究院中级工程师/主要研究方向:景观规划与设计

    通信作者邮箱Corresponding author Email):tdscgj_kz@163.com

    ZHANG Bin, male, was born in 1981. He is the intermediate engineer of Urban Planning and Design Institute in Tianjin University. Major research direction: landscape planning and design.

    王新亮 / / 1983年生 / 天津市城市规划设计研究院高级规划师/主要研究方向:市政工程规划

    WANG Xinliang, male, was born in 1983. He is the senior unban planner of Tianjin Urban Planning and Design Institute. Major research direction: municipal engineering planning.

    摘要:为了在城市建成区更新改造中更好地解决内涝问题,以天津市南开区为例,从承灾体的脆弱性和暴露度两方面考虑,采用指标体系评估方法进行内涝风险评估;同时考虑建成区存在现状复杂、改造难易程度不一等特点,叠加城市建设可实施性评估因子,据此划分城市内涝防治引导区划。提出构建区域整体绿色防涝体系的同时,针对不同分区确定可操作性较强的规划及对策,为城市建成区的内涝防治工作提供参考。

    关键词:城市建成区;内涝风险评估;引导区划

    Abstract: For better solving waterlogging issue in urban built-up area renewal, the paper takes Nankai District of Tianjin as the example, considering the vulnerability and exposure, indicator system evaluation as the research method to assess waterlogging risks. And considering current situation and the difficulty level of the built-up area renewal, the paper incorporates urban construction executable evaluation factors to divide urban waterlogging prevention and control sections. While building up an entire green waterlogging prevention system, according to section conditions, the paper proposes feasible planning measures, and offers reference to waterlogging prevention and control work in urban built-up area.

    Key words: urban built-up area; waterlogging prevention and cure evaluation; the guidance zoning

    近年来,洪涝灾害频发给我国城市发展带来巨大冲击,“城市看海”现象成为众多大城市面临的难题[1]。城市建成区是人民生活最迫切需要提升环境品质的区域,将城市内涝风险评估作为更新规划的前置十分必要。同时,由于建成区存在多种现状因素和实际情况影响,其内涝风险评估结果应结合实际改造难易程度、可行性、时序等考虑,并据此提出可操作性较强的规划策略。

    1 评估方法的选取和修正

    目前,国内外城市内涝风险的评估方法主要有三种:一是基于历史灾情的数理统计法,计算简单但长时间序列的历史观测数据较难获得,导致这种方法在实际应用上具有较大局限性。二是基于情景模拟的水文水力学模型与仿真模拟法,具有较好的可视性;但这种方法数据量大,模型复杂。三是基于灾害特点的指标体系评估法,相比以上两种方法而言模型简单,所需数据量较小,计算便捷,通用性强[2]。本文以评估普适性与建设指导性作为主要原则,从脆弱性和暴露度两方面考虑构建评估体系,并纳入城市可实施性评估因子,增强评估结果对更新改造实施的指导。

    2 研究实例范围

    南开区位于天津市中心城区西南部,总面积40.64 km22015年常住人口113.6万人,城市建设平均容积率1.28,是中心城区城市化程度较高的区域。南开区原系天津老城南边的开洼地,至今仍存在大面积低洼地区。

    3 南开区内涝形势及成因

    3.1 南开区内涝形势

    天津市近年因暴雨频发造成内涝, 城市安全和人民生活受到了极大的影响。2016720日,天津市遭遇50年一遇的特大暴雨,据天津市排管处数据及暴雨期间各区上报情况,中心城区共有69处积水片(积水深度20 cm以上),其中南开区积水片区共14个,占总数的20.3 %,是中心城区6个行政区中内涝片区较多的行政区(表1)。

    3.2 南开区内涝成因

    南开区的严重内涝是特定的气候、水文、地势、排水系统和城市化等多重因素共同作用的结果。

    1)气候因素:天津市是暖温带气候,6月~8月降水可占全年的80%,极易造成夏季洪涝灾害;加之全球气候变暖导致极端暴雨天气的频次、强度均有所增加。

    2)水文因素:天津市城区地处“九河下梢”,由于潮流顶托,造成一级河道水入海不畅,水位抬高,致使沿岸排水口门及城区二级河道涝水不能及时汇入,进一步加剧了城市内涝风险。

    3)地势因素:南开区大部分地区高程较低,其中北部是大片低洼地,易形成暴雨积水区;且区内河道堤顶高程较低,易发生河道水漫堤现象。

    4)排水设施因素:南开区大部分建成区的建设年代较早,管网老旧,设计暴雨重现期一年一遇,仍存在部分合流制区域,难以与中心城区排水需求相匹配。目前,区内人均占有排水干管长度为0.07 m,仅达到欧美国家的1/601/80[3]。通过对区内各积水片的调查发现,咸阳路等路段的雨水干管管径偏小;津河、卫津河等二级河道存在过水断面偏小、提升泵站能力不足或无泵站等状况(图1)。

    5)城市化因素:快速城市化加剧了城市热岛效应、提高了综合径流系数[4];城市扩张导致自然水体的减少,极大削弱了地表的排水蓄水能力。

    4 南开区内涝风险评估

    面对南开区严峻的内涝防治形势,针对其内涝成因,本文建立了基于地形、水网、排水设施、人口、用地等数据的内涝风险评估体系,结合南开区现状建设情况、未来规划方向等可实施性因素,提出南开区的内涝防治引导区划,从规划编制、政策引导等层面提出内涝防治对策。

    4.1 南开区内涝风险评估

    在降水强度相同的情况下,南开区内涝风险主要取决于受灾体脆弱性和暴露度的差异,在研究区内体现为地形高程、河道漫堤风险、市政管渠覆盖程度、现状泵站数等脆弱性影响因子和人口密度、城市功能重要性等暴露度影响因子。根据数据获得的普遍性与通用性确定如表2中的六项风险评估因子及其对应的量化参数。

    1)地形高程

    南开区的高程值大多分布在1 m5 m(大沽高程,下同)区间内(图2)。其中,高程值小于1 m的地块多为河道水系,内涝风险小;高程值大于4 m以上的地块主要分布在中部(鞍山西道至天拖北道以南)、南运河河堤两侧和鼓楼街区,内涝风险较小;而高程值介于2 m3 m之间的大面积区域主要分布在南开区北部(鞍山西道至天拖北道以北),其中长江道与咸阳路交口周边地区地势最为低洼,内涝风险大。

    2)河道漫堤风险

    通过对区内一、二级河道两侧堤顶高程分析,发现北部南运河堤顶高程为3.5 m5.6 m,津河堤顶高程为2.6 m4.4 m,均高于两侧用地高程,高差在0.5 m2 m。其中,津河北段堤顶高程仅为2.6 m2.7 m,暴雨时期河道水位升高,极易发生河道水漫堤现象(图3)。加之南开区北部地区地势低洼,河道两侧地块的内涝风险相当高。

    3)管渠覆盖程度

    管渠覆盖率(m/m2)是区域管渠长度(m)与区域面积(m2)的比值。因南开区目前管道标准各不相同,以1 km2收水面积为例,南开区三年一遇设计标准下排水流量约为6 m3/s,一年一遇设计标准下排水流量约为4 m3/s,以二者比值1.5为修正系数,三年一遇排水区域乘以该系数进行修正。计算得到管渠覆盖率在0.001 m/m20.004 m/m2区间范围内,其值越低,内涝风险越高。

    4)现状泵站

    现状泵站包括雨水泵站和河流泵站,泵站数越少,内涝风险越高,反之则越低。通过统计南开区现状泵站数,得知地块内泵站数量范围03个。

    5)人口密度

    人口对南开区内涝风险的影响主要体现在居住安全性、出行便利性及效率等方面。区内人口比较密集的区域主要集中在中、北部和南北向主干道红旗路东侧沿线地区。根据图4可得到人口密度分布(表3)。

    6)城市功能重要性

    内涝造成的经济和社会损失与城市功能重要性呈正相关。依据不同城市功能地块与生产、生活的关联度及人流量,将其的重要程度划分为04级,重要性逐级递增。将大型文化设施、医疗设施、体育设施、商业设施、旅游景区等划为重要性最高的级别(图5),具体分级见表3

    以上六项风险评估因子具有不同的计量单位和数量级,相互之间不具有可比性,所以要采用百分制评分法对各因子进行无量纲化处理,得到各因子的评分Si ,并通过专家打分法确定各风险评估因子的权重Wi (表4)。

    在以上各项风险评估因子的基础上,根据近期暴雨积水片数据P(图6)对评估进行修正,有暴雨积水地块赋值为100,无暴雨积水地块赋值0。南开区各地块内涝风险评估数值R可根据公式(1)计算得出,并对应不同的风险等级(表5)。对南开区展开的内涝风险评估,其结果如图7

    1 南开区排水系统规划图

    Figure 1 Planning Map of Drainage System In Nankai District

    2 南开区高程分析图

    Figure 2 Analysis Map of Top Height In Nankai District

     

    3 南开区河道堤顶高程分析图

    Figure 3 Analysis Map of Top Height of Riverbanks In Nankai District

    4.2南开区内涝防治建设引导区划

    南开区的内涝防治可实施性评估主要参照现状土地存量、近期建设计划和未来规划方向进行,包括可更新地块、近期建设改造道路、重点开发地块等可实施性因子(图8、图9、图10)。

    1)可更新地块

    可更新地块现状建设量小,更新成本较低,内涝防治可操作性高。此类地块主要分布在西侧西营门地区及红旗路沿线,用地性质多为已经搬迁或面临改造的工业园区、科技园和等待重建的荒地,未来建设过程中应合理设计,预先解决排涝问题。

    2)近期建设改造道路

    结合道路的改造建设,可进行排水管网改造升级,提高排涝能力。近期考虑对天拖等地块进行道路建设,并对咸阳路等部分道路提升改造,同时按照三年一遇新标准完善排水管网系统,将尚为合流制的地块改为分流制,以增强管网排水能力,符合中心城区高强度、高密度的建设环境。

    3)重点开发地块

    重点开发地块对于内涝防治的标准要求较高,近期实施的可能性大。此类地块聚集在西侧西营门及天南大校区周边。这些地块原为商业、工业或高校,周边商务办公、零售商业、生活居住等业态完整,是南开区未来城市发展重要节点,内涝问题亟待解决。

    通过将内涝风险评估和以上可实施性因子叠加,得到南开区内涝防治可实施性评估(图11)。图中深灰色内涝风险最高,红色为未来可建设进行防治内涝区域,两者相重合的区域为最紧迫且可进行建设改善区域。依据内涝防治可实施性评估进一步划分南开区内涝防治建设引导区划图。该区划分为先行区、重点区和引导区(图12)。先行区为内涝风险最高、防治必要性最大、最具可建设性的地区,包括西营门、天拖、科技广场;重点区为内涝风险高、防治必要性较大、具备一定可建设性的地区,包括咸阳路南、西湖道、万兴街地区;其他地区为引导区。

    式中:Rj ——地块j 的内涝风险评估结果;

    Si ——风险评估因子Bi 的评分值;

    Wi ——风险评估因子Bi 的权重值;

    n ——风险评估因子个数;

    Pj ——地块j 近期暴雨积水赋值。

    4 南开区人口分布图

    Figure 4 Population Distribution in Nankai District

    5 南开区城市功能重要性分布图

    Figure 5 Distribution of Importance of Urban Function In Nankai District

    6 南开区近期暴雨积水片分布图

    Figure 6 Distrbution of Water Area Caused by Recent Rainstorms In Nankai District

    5 南开区内涝防治对策

    首先从整体的角度出发,完善各级绿道、斑块,构建全区绿色防涝体系。同时划分引导片区,结合现状改造的可实施性考虑“灰绿结合”的具体策略。

    5.1 构建南开区整体绿色防涝体系

    城市绿地不仅具有塑造城市景观和提供休闲游憩场所的功能,内涝灾害时兼具蓄水减洪作用。因此要合理利用南开区现状绿地,在城市绿色廊道与斑块绿地两个层面规划完善绿地系统,构建雨水调蓄利用的城市海绵体系[5]

    5.1.1 城市绿道系统

    构建城市、社区、邻里三个尺度下的线性绿地空间作为城市海绵体系的廊道,连接绿地斑块,并结合城市慢行系统形成绿道体系(图13)。一级绿道规划宽度120 m150 m,由现状市级环城绿道、南运河绿道和规划津河绿道构成,形成绿道主要骨架;二级绿道规划宽度60 m90 m,由在建天拖绿道和规划西营门绿道、水上西路绿道构成;三级绿道规划宽度20 m30 m,由邻里范围内带状绿地构成。上述绿道体系不仅可以创造市民休闲游憩的活力场所,同时结合雨水花园、下凹绿地、植草沟等具体技术措施可削减雨水径流,减少城市内涝,实现绿色基础设施的作用。

    5.1.2 城市斑块系统

    绿地斑块对丰富城市绿色空间、控制暴雨径流量作用明显,可对南开区现有绿地斑块进行改造,并增加各级斑块数量,以减轻内涝(图14)。一级斑块为城市现有大规模绿色空间,主要为水上公园、长虹公园、南翠屏公园、绿水园等现有城市公园,对公园进行蓄滞区域高程改造,保证总体竖向高程低于周边汇水分区,便于雨水汇流。二级斑块为社区公共绿地、街边花园等小规模绿色空间,可在建成区改造中灵活设置,规划中着重增加此级别绿地。三级斑块可结合邻里公共空间规划下凹式绿地、雨水花园,与建筑绿色屋顶等具体设施相结合削减地块内部径流,可在小范围改造现有管网的前提下,提高防涝能力。

    5.2 南开区内涝防治建设引导

    5.2.1 先行区对策

    先行区具备新建与扩建可能性,在建设之初即可采用高标准建造市政雨水管网,统筹安排区域内大型公园绿地、下沉广场等大海绵系统,并尽可能在工程及非工程措施中运用低影响开发理念以增加源头减排,构建完善的内涝防治系统[6]。新建、扩建地块由于规避了原排水设施建设投资以及设施拆除费用,也免于建成后再单独筹措内涝防治资金,内涝防治成本相对较低。从区域统筹角度考虑,先行区新建、扩建地块应承担一部分周边难于改造地区的暴雨径流,以降低城市内涝防治的难度和整体成本。

    5.2.2 重点区对策

    重点区的工程性内涝防治对策则应充分结合近期改建计划,灵活运用灰绿结合的策略,并采用低影响开发理念,以尽可能做到“慢排缓释”和“源头分散”。各重点区在灰绿结合的策略制定上应实事求是、因地制宜,抓住主要问题与矛盾:灰色基础设施较完善的地块可主要侧重绿色生态设施的构建;灰色基础设施建设较差的地块应同步统筹,考虑灰绿结合,在弥补遗留问题的同时,注重提升绿色生态设施的建设水平。

    5.2.3 引导区对策

    引导区多为成熟建成区,且内涝风险较低、防治紧迫性较小,无需“治”涝,但应侧重“防”涝。因此,引导区可采取局部改建措施,结合沿河公园、绿地等建设分散、点状的多功能调蓄设施,比如建设储水池、雨水罐、绿化屋顶、透水铺装等,以加强雨水消纳能力,减轻对排水设施压力,增加城区可用水资源量,减轻下游河道排水压力,同时可减轻城市径流污染,减少对河湖水系的不良影响。

    6 结论

    对于城市建成区的更新改造而言,加入城市实施性评估的内涝评估综合考虑了城市的防灾需要和城市发展情况,相比于传统的内涝风险评估,能够为城市建设管理提供建设引导规划,便于制定稳步有序的内涝防治建设计划和切合实际的防治对策,提高城市对内涝灾害的抵御能力。

    7 南开区内涝风险评估图

    Figure 7 Assessment Image of Waterlogging Risk In Nankai District

     

    8 可更新地块分布图

    Figure 8 Distribution of Renewable Plots

     

    9 近期建设改造道路分布图

    Figure 9 Distributions of Recent Reconstructed Roads

     

    In recent years, frequent waterlogging strongly impacts the development of cities in our country, causing "ocean in the city", a challenge many big cities face [1]. Because built-up area is regions where environment and live qualities are in urgent need of improvement, it's necessary to put city waterlogging risk prevention and cure evaluation as a precondition of update planning. Meanwhile, given the impact of various current factors and the physical truth in built-up area, the waterlogging risk evaluation result should incorporate with the complexity, feasibility and sequence of practical renewal. And operable planning strategy should also be proposed based on that.

     

    1 Selection and Correction of Evaluation Methods

    There are three main methods of waterlogging evaluation in domestic and abroad. The first method is based on the mathematical statics of historical disasters. This method is simple on calculation but obtaining the enormous observation data from long history is not easy. Thus, the method has great limitations in practical applications. The second method is based on hydrological and hydraulic model and simulation method. It has great visuality but the data amount is huge and the model is complex. The third is evaluation method of indicator system based on the feathers of disasters. Comparing with previous two methods, it has advantages of simple model, small data requirement and strong versatility [2]. We take universality and construction guidance as main principle, considering the construction system from vulnerability and exposure, and combining with the urban construction executable evaluation factors, to strengthen the guidance effect of evaluation result to renewal implement.

     

    2 Scope of the Research Example

    Located in the southwest of downtown Tianjin, Nankai district has a population of 1136 thousand until the year of 2015, with a total area of 40.64 square kilometers. It's a higher civilized region among central urban area with an urban construction average plot ratio of 1.28.Nankai district was an open sinkage area lying in the south of old town of Tianjin, and there are still large scale of low-lying land there.

     

    3 The Situation and Reason of Waterlogging In Nankai District

    3.1 The Situation of Waterlogging In Nankai District

    Waterlogging resulting from rainstorms in Tianjin brought extreme impact to urban security and citizens in recent years. On 20th July 2016, Tianjin suffered from the worst torrential rain in 50 years. According to the data from Tianjin Drainage Office and report from all districts during the raining, there were totally 69 pieces of water area in downtown (20 cm or deeper), including 14 pieces in Nankai District, accounting for 20.3% of the total. It's one of administration districts with more water pieces in six districts of downtown (table 1).

    3.2 The Reason of Waterlogging In Nankai District

    Severe waterlogging in Nankai District is a comprehensive result from multiple factors such as specific climate, hydrology, topography, drainage system and urbanization.

    (1) Climate Factor: Climate in Tianjin is warm. Precipitation amount from June to August accounts for 80% of whole year, which tends to form summer flood; and global-warming has increasing the frequency and intensity of extreme rainstorms. (2) Hydrology Factor: Tianjin downtown is located at the end of nice rivers. Due to the tidal topping, the water in first-class rivers cannot smoothly access to the ocean and thus water level is raised. As a result, water in coastal drainage gate and second-class rivers cannot run into the first-class rivers, further exacerbating the risk of urban waterlogging.

    (3) Topography Factor:Most area in Nankai District are at low elevation, in which the north part is a large bottomland, where tends to form water areas after rainstorms; plus the low river embankment top, it's easy to cause river overtopping situation.

    (4) Drainage Facility Factors: Most built-up area in Nankai District built earlier with old pipe nets were designed for worst rainstorms in one year. And there are still some confluence areas which can hardly meet the drainage demand of downtown. Now the per capita possession of drainage mains pipe length is 0.07 m, which is only 1/60-1/80 of developed countries [3]. Through the investigation of each water area in the district, we found the diameters of main rainwater pipes in roads such as Xianyang Rd are too small; the second rivers like Jinhe River and Weihe River have problems such as small cross section, scare lift ability of pump station lack of pump station (figure 1).

    (5) Urbanization Factors: Rapid urbanization exacerbates the urban heat island effect and improves the integrated runoff coefficient [4]; urban expansion leads to a reduction in natural waters, and weakens the drainage ability of the surface.

     

    10 重点开发地块分布图

    Figure 10 Distributions of Key Development Plots

    11 南开区内涝防治可实施性评估图

    Figure 11 Executable Evaluation Image of Urban Construction In Nankai District

    12 南开区内涝防治建设引导区划图

    Figure 12 Guidance Zoning Image of Waterlogging Prevention and Cure Construction in Nankai District

    13 南开区绿道系统规划图

    Figure 13 Planning Image of GreenwaySystem In Nankai District

    14 南开区绿地斑块规划图

    Figure 14 Planning Image of Green Plagues In Nankai District

    4 Risk Assessment of Water logging in Nankai District

    Facing the severe situation of water logging prevention and cure in Nankai District, for the waterlogging reasons, a waterlogging risk assessment system based on the data of topography, network of rivers, drainage and location is created. A guidance zoning of waterlogging prevention and cure is proposed combining with executable factors such as current construction and future planning direction in Nankai District. And prevention and cure strategy is proposed from the aspect of planning formulation and policy guidance.

    4.1 Waterlogging Risk Assessment in Nankai District

    Under the same precipitation intensity, the waterlogging risk in Nankai District mainly depends on the difference on vulnerability and exposure of affected objects. In the research area, vulnerability is reflected as terrain elevation, risk of river levee, municipal pipe coverage and current pump stations; while exposure is reflected as factors like population density and importance of urban function. The six risk assessment factors and their quantization parameters based on the universality and versatility of the data are determined as below in table 2.

    (1) Terrain Elevation

    The elevation values of Nankai District are mostly distributed at the range of 1-5 m (estimated value, the same below) (figure 2). In the map, blocks below 1m are river water system who has less risk of waterlogging; areas above 4 m are mainly distributed in the middle part (south of Anshanxidao - Tiantuobeidao), banks of Nanyunhe Canal and Gulou district with low waterlogging risk; and areas between 2-3 m are on the north of Nankai District (north of Anshanxidao - Tiantuobeidao) including region around the cross of Changjiangdao Street and Xianyanglu Road which has most waterlogging risk.

    (2) River Levee Risk

    By analyzing the bank elevation value of first and second class rivers, we found on the north part, top height of Nanyunhe Canal bank is 3.5-5.6 m; top height of Jinhe River is 2.6-4.4 m, both of which are 0.5-2 m higher than nearby area. Elevation of Jinhe River north section is only 2.6-2.7 m, and water level would rise in rainstorms tending to cause flooding over banks (figure 3). In addition to the low terrain in the north of Nankai District, there is extreme high risk of waterlogging on bank zone.

    (3) Pipeline Coverage

    Pipeline coverage ratio (m/m2) is the ration of the length (m) of the zone pipe to the area of the zone (m2). The pipeline standards are various in Nankai District. Take area of receiving water in 1 square meter as an example, drainage flow under the design for worst in 3 years is about 6 m3/s, while for worst in 1 year is about 4 m3/s, take 1.5, the ration between them as correction factor, correct drainage area for worst in 3 years by timing the factor. The result of pipeline coverage is between 0.001-0.004 m/m2. The lower the result, the higher the waterlogging risk.

    (4) Current Pump Stations

    Current pump stations include rainwater pump stations and river pump stations. The less the pump stations, the higher the waterlogging risk, vice versa. According statistics data, there are 0-3 pump stations in Nankai District.

    (5) Population Density

    The impact of population on the waterlogging risk is mainly reflected in safety of residence, travel convenience and efficiency. Densely populated areas in the district is mainly concentrated in the middle and north region and along eastern side of Hongqidonglu Road,a main road. Population density distribution could be acquired according to population date in figure 4 (table 3).

    (6) Importance of urban function

    The economic and social losses caused by waterlogging are positively related to the importance of urban function. According to the relevancy between different urban function blocks and the product and life as well as visitors flow, the importance is divided into level 0-4, with increased importance. Large culture facilities, medical facilities, sport facilities, business facilities, tourist attractions are in the highest level (figure 5). See details in table 3.

    The six factors above are not comparable with different unit of measurement and magnitude. Thus, the factors should be dimensionless processed using percentage rating, to obtain score Si, and then determine the weight Wi of each factors through score by experts (table 4). rea caused by recent rainstorms (figure 6), based on all risk assessment factors.

    A plot with water area is 100, while without water area is 0. R, assessment value of waterlogging risk in Nankai District, could be obtained according to formula (1), and they are responding to different levels (table 7). Assessment Results of waterlogging risk in Nankai District see figure 10 bellow.

    4.2 Guidance Zoning for Waterlogging Prevention and Cure Construction In Nankai District

    Executable assessment of waterlogging prevention and cure in Nankai District is mainly based on executable factors such as current land stocks, recent construction plan and future planning direction, including practicable factors like renewable plots, recent reconstructed roads, and key development plots (figure 8, 9, 10).

    (1) Renewable Plots

    Renewable plots have features of small construction amount, low renewal cost and high waterlogging prevention and cure maneuverability. This kind of plots is distributed around Xiyingmen area and along Hongqilu Road, and most of them are industry zones and Science Parks which already moved away or waiting for reconstruction and wasteland to be renewal. The design for their future construction is rational, and has addressed the drainage problem in advance.

    (2) Recent Reconstructed Roads

    Drainage pipe nets could be updated combining with road reconstructions to improve flood storage capacity. Recently, plots like Tiantuo are been considered to be reconstructed, and roads like Xianyanglu to be improved, in order to change the combined system to separate system and fit the high-strength and highdensity construction environment in downtown.

    (3) Key Development Plots

    The key development plots have higher requirement for waterlogging prevention and cure standards, and will probably implement in recent future. These plots concentrate around Xiyingmen and Nanjing University. They are used to be business area, industry zone or universities with all types of operation like business, retail and residence. As a key point of future urban development in Nankai district, its waterlogging problem has to be settled urgently.

    By combining waterlogging risk assessment and executable factors, we can obtain waterlogging prevention and cure practicable assessment (figure11).the dark grey area in the map has highest risk of waterlogging, the red is area for the future construction and prevention of waterlogging. And where the two overlapped is area in urgency and could be constructed for improvement. Further divide Nankai District according to waterlogging prevention and cure practicability to create guidance zoning map. The district can be divided into advance zone, key zone and guide zone (figure 12). Advance zone has the highest waterlogging risk, the most prevention and cure necessary and most renewability including Xiyingmen, Tiantuo, Science Square; key zone has high waterlogging risk and urgent necessary of prevention and cure, and has certain constructability including south of Xianyang Road, Xihu Road and Wanxing Street area; besides are guidance zone.

     

    5 Waterlogging Prevention and Cure Strategy in Nankai District

    Start from the holistic perspective to improve greenways and plaques on each level and construct a whole green waterlogging prevention and cure system in the district. Meanwhile, divide the guidance zone and consider the specific strategy of "grey-green" combining current renewal practicability.

    5.1 Construct Green Waterlogging Prevention and Cure System in Nankai District

    Urban green space can not only create a city view and provide a place to relax but also could provide function of water storage and flood reduction in waterlogging disaster. As a result, we should properly take advantage of current green space in Nankai District; improve the green space system from aspect of urban green corridor and plaques green space, to construct urban sponge system for rain water storage and usage [5].

    5.1.1 Urban Green Way System

    Establish linear green space under city, community and neighborhood as corridor of urban sponge system, to connect green space plaques to form greenway system by combining urban low speed system (figure13). Planned width of first level greenway is 120-150m. It consists of current city level ring road greenway and planned Jinhe Road, forming the main greenway frame; planned width of second level greenway is 60-90 m, it consists Tiantuo greenway in-constructing, planned Xiyingmen greenway and Shuishangxilu Road green way; width of third level greenway is 20-30 m, and it consists banded greenway in neighborhood.

    Above greenways can not only create activity places for citizen to relax and visit, when combining with specific technical measures like rainwater garden, subsided green space and grass gutter, it can also reduce rainwater cutoff, remit waterlogging and provide the function of green facilities.

    5.1.2 Urban Plaques System

    Green space plaques are effective in enriching urban green space and controlling storm runoff. Renewal current plaques and increase amount of plaques on each level in Nankai District to reduce waterlogging (figure 14). First level plaques are large scale urban green space, which are mainly current urban parks like waterpark, Changhong Park, Nancuipin Park, Lvshui Park. Improve elevation of drainage storage area in the park, to make sure the holistic elevation is below watershed partition nearby, and rainwater can converge. The second level plagues are small scale green space like community public green space and street garden, which can be flexibly set in renewal of built-up area, and mainly increased in the plan. The third plagues can be combined with neighbor public area to plan subsided green space, rainwater garden and green roofs to reduce internal cutoff. It can improve drainage ability without large scale renovating existing pipeline nets.

    5.2 Construction Guidance of Waterlogging Prevention and Cure in Nankai District

    5.2.1 Strategy for Advance Zone

    Advance zones have possibility of new construction and expansion. At the beginning of construction, these zones are designed with high standard municipal pipeline nets, and large scale sponge systems like large park green space, subside squares are arranged as a whole in the zone. Low-impact development idea is used as much as possible in the engineering and non-engineering measure, in order to reduce emission from source and construct well-built prevention and cure system of waterlogging [6]. New built and expansion plots circumvents the previous construction and deconstruction investment of drainage facilities, thus, have no need to raise funds for waterlogging prevention and cure, and the cost is relative low. Consider from the aspect of regional co-ordination, new built and expansion plots in advance zone should take partial responsibility of the rainstorm cutoff around where have drainage difficult to lower down the difficulty of waterlogging prevention and cure as well as the total cost.

    5.2.2 Strategy for Key Zone

    Engineering strategy of waterlogging prevention and cure in key zones should be combined with recent reconstruction plan, and flexible use the strategy of "greygreen".

    Incorporate with low-impact development idea in proper place, to realize "slow drain and release" as well as "disperse from source". When make strategy of "grey-green" in each key zone, we should respect truth, adjust measures to local conditions and seize the principal problem and contradiction: in plots with well-built grey facilities, construction of green ecological infrastructure should be emphasized; in plots with poor grey infrastructure, "grey-green" should be considered, making up the debt while improve construction level of green ecological facilities.

    5.2.3 Strategy for Guidance Zone

    Most guidance zones are built-up zones with low risk of waterlogging and less urgency of prevention and cure. The emphasis of these zones is "prevention", not "cure". Thus, partial renewal measures should be taken in guidance zones, together with parks along river or green space to construct dispersive punctate multi-function water storage facilities, such as tanks, rain water sinks, green roof and penetrative pavements. Use these methods to strengthen the ability of absorbing rainwater, reduce pressure on drainage facilities, increase water resources quantity in urban areas, reduce downstream drainage pressure, as well as reduce urban runoff pollution and reduce adverse effects on rivers and lakes.

     

    6 Summary

    For the renewal of urban built-up areas, waterlogging assessment with urban practicable assessment takes into the urban disaster prevention need and urban development situation. Comparing to traditional waterlogging risk assessment, it can provide construction guidance zoning to urban construction management, and is convenient to make steady and orderly waterlogging prevention and cure construction plan as well as practical prevention and cure measures, to improve the city's ability to resist waterlogging disasters.

     

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    [6] 蔡凯臻.缓解雨洪内涝灾害的城市设计策略——基于街区层面的暴雨径流过程调控[J].建筑学报,201510):73-78

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    (整理:赵迪 译:申惠波)

     

     

     

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