摘要
土地開發行為會造成集水區內之地表逕流量性質改變，讓原規劃水路之通水能力不敷使用，或已改善之淹水地區可能再度引發淹水，行政院刻正積極推動流域綜合治理計畫，針對流域或集水區內之土地變更或開發行為，本於「出流管制及逕流分擔」原則，制定一套地區減災防洪標準，排除人為所造成的淹水災害。
出流管制及逕流分擔為針對已經完成規劃或淹水改善的地區之排水，因為土地開發或變更等因素，造成地表不透水面積增加，使得地表逕流量增大，透過低衝擊開發(LID)之雨水貯留、延緩洪峰時間遲滯、增加雨水入滲量及滯洪設施，將開發後的洪峰流量減洪至開發前的流量及管制為下游可允許之排放量，惟各類排水皆有其保護標準以及不同土地開發亦有其開發管制條例，本研究探討各類排水規範之水路設計及防洪保護標準之水文水理分析之差異，並分析相關的排水法令或設計規範，是否適合於出流管制及逕流分擔的理念，並選定較佳之滯洪池配置方式，以達成『逕流分擔與出流管制』之目標。
本研究針對開發前後所造成之地表逕流增加量，直接採用在槽滯洪池方案減洪以進行檢討，並整合效益分析以選擇較佳之滯洪容量配置方式。第一個案例下游銜接水路為區域排水，採用單一集水區之排水系統出口作為排水放流量管制點，依各類排水設計規範檢核可允許之排放量以進行出流管制，針對合理化公式及修正三角單位歷線法對排水設施規範之設計參數進行探討，最後分析結果顯示，對於水路匯入區域排水位置作為管制點而言，應採修正三角單位歷線法推估10年重現期距開發前之洪峰流量作為下游允許排放量，並依開發前後之流量歷線，計算減洪量所須滯洪池容積來配置滯洪池為宜。
第二個案例則分析兩個串聯的上下集水區、對此區內之水路及其水文水理之差異性進行分析，並採用可使各子集水區及流出過程得以一致性估算方法，進行系統水文水理分析，最後採逕流分擔方式，在上下游集水區內各設一個在槽式滯洪池予以滯洪，並計算土地開發後流出洪峰所需減少之洪流量，最後經由工程效益分析，對於在上游子集水區出口處設滯洪池，所須的滯洪容積加總越小，經濟效益較大。

Studying of the design runoff apportion and
outflow control of small catchment
Lai Ming-Lun
Fred Chou
Department of Hydraulic and Ocean Enginnering
& National Cheng Kung University

SUMMARY
In this study, the development of the land caused by increased surface runoff, the direct use of detention pond programs to reduce peak flows in order to conduct a review, and benefit analysis and the use of detention pond is used to select a preferred configuration capacity. The first case ,the channel joint downstream is region drainage. Use the outflow exit of single watershed for outflow control point. To proceed the “outflow control” according to different drainage design norm’s allowable discharge capacity; discuss the parameter of drainage facilities norm in accordance with rational formula and fixed triangle unit hydrograph method, examine it’s influence factor and applicable condition. Result analysis, for downstream is region drainage,it should be use ten years recurrence interval’s peak discharge in the fixed triangle unit hydrograph method to emissions standards,and use discharge hydrograph to calculate to reduse runoff volume.
The second case analyze the differences between upstream and downstream basin, channel and its Hydrologic and hydraulic analysis within many watersheds, and select and adopte all sub-catchment and outflow process the same method to do system Hydrologic and hydraulic analysis. Lastly the “runoff apportion”, setting up a detention basin in the channel case in each upstream watershed and downstream watershed to detention the flood and calculate the decrease flow that flood peak needs. By efficiency result analysis, choosing a better way in the upstream basin to set up the detention basin, the total detention capacity is smaller, the economy efficiency is larger. If the detention perimeter’s revetment, gravity retaining wall replace vertical retaining wall,the detention and perimeter less effect best benefit design .
Key word：outflow control,runoff apportion,drainage design plan study,detention basin in the channel case

INTRODUCTION
Land development will result in changes in the catchment runoff, let the original plan of the waterway through the flow section is not enough. Or the improved flood area might touch the flood off again. Executive Yuan are actively executing the “Integrated Basin Management Project”, aiming at the land altering or developing within the basin or catchment, establish a disaster area flood control standard based on the “outflow control and runoff apportion” principle, excluding floods cause by operational factor.
Due to land developing or altering, the already planned and improved flood area and drainage cause impervious coverage increased and enlarge the surface runoff, the “outflow control and runoff apportion” wish to decrease the flood discharge after the development to planned discharge before development and fits the downstream allowance discharge through LID rain serving、postpone the peak time、increase rain infiltration and detention basin.
This case study, physiographic factors and other parameters of the catchment hydrological parameters is used Kau Kow drainge Yuanlin, Changhua County ditch drainage areas. Including the use of the catchment area, the location of the main waterways and drainage path length mainstream, catchment land. Most factors such as improving water after section, detention pond setting address, after the development of land use and so do the reasonable assumptions. Does not consider the impact of external factors such as the degree of public acceptance, and the land compensation costs are $ 2,200 per square meter in order to calculate. The rainfall is used over the years of rainfall data Yuanlin near Tow Ben rainfall stations as a basis for analysis.
METHODS
This study was designed to explore the waterways design and drainage specifications of all kinds ,and differences hydrological analysis of flood protection standards. Analyze if current ordinance or drainage design norm is proper for the concept of “outflow control and runoff apportion”, choosing a better way to set up the detention basin to accomplish the goal of “outflow control and runoff apportion”
RESULTS AND DISCUSSION
Case One analysis showed that for downstream is region drainage,it should be use ten years recurrence interval’s peak discharge in the fixed triangle unit hydrograph method to emissions standards,and use discharge hydrograph to calculate to reduse runoff volume.
Case Two analysis showed the following table, by efficiency result analysis, choosing a better way in the upstream basin to set up the detention basin, the total detention capacity is smaller, the economy efficiency is larger. If the detention perimeter’s revetment, gravity retaining wall replace vertical retaining wall,the detention and perimeter less effect best benefit design

CONCLUSION
(A) For downstream is region drainage,it should be use ten years recurrence interval’s peak discharge in the fixed triangle unit hydrograph method to emissions standards,and use discharge hydrograph to calculate to reduse runoff volume.
(B) When both the upstream and downstream positions can be applied to set up detention pond, you should explore the different capacity of downstream flood detention pond reduce individual combinations of results, in order to determine the best design of the factors.
(C) Due to land in urban areas is more difficult to obtain, and no suitable place to set up when detention pond can be used low impact development (LID) of rainwater storage, delay peak time lag, increase rainwater infiltration and detention facilities, and other ways to cope with the application.
(D) When the detention pond retaining wall revetment is vertical, so the larger detention pond perimeter impact on project costs, so in this case the use of a detention pond total funding of two relatively small detention pond.

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