103年度客雅溪上游河道漂浮物攔阻設置方案評估與青草湖繞庫排砂效益分析(附光碟)

青草湖水庫位於新竹市南區客雅溪中游，為新竹地區早期兼具灌溉及觀光功能之水庫與著名風景區。庫區上游係屬山谷地形，流域裸露之地層有上新世卓蘭層與更新世之沖積層，土質鬆軟易受沖蝕，汛期易造成土方量流失流入青草湖，使蓄水容量逐年銳減，致使防洪和灌溉功能喪失，目前僅保留觀光遊憩功能，並由新竹市政府負責管理。
本計畫目的係透過評估青草湖上游河道漂浮物攔阻設置方案與設置位置可行性，分析是否有適合之攔阻工法與設置位置以減少漂浮物（如：竹子）進入青草湖。並對繞庫排砂方案應用於青草湖之排砂效益進行綜合分析，評估以繞庫排砂方案減少泥砂入流進入青草湖之可行性。各工作項目概述如下：
一、 客雅溪上游河道漂浮物攔阻設置方案評估
(一) 青草湖上游既有之河道地形資料調查蒐集
調查蒐集計畫區內坡向、坡度、高程以及2005、2008與2012年之斷面等資料蒐集。
(二) 青草湖週邊地質資料調查蒐集
調查蒐集客雅溪與青草湖之土壤、地層、地質構造與斷層等資料。
(三) 河道漂浮物（如：竹子）攔阻工法之蒐集整理
蒐集整理河道漂浮物攔阻工法，主要可分為格柵攔截設施（包含全斷面、潛壩型以及簡易格柵）與攔污索。
(四) 客雅溪上游河道適當之漂浮物攔阻工法設置地點選定分析
考量客雅溪上游河道漂流物主要來源、河道寬度、淹水潛勢災害區段、設置地點之地層與地質條件以及生態保育等因素，初步規劃客雅溪上游河道漂浮物攔阻工法設置地點方案。
(五) 設置漂浮物攔阻工法對客雅溪上游河道各重現期流量之水位及通洪能力影響分析
本計畫以HEC-RAS模式模擬漂浮物攔阻工法方案，於各重現期流量條件下，客雅溪上游河道之水位及通洪能力影響分析。
二、 青草湖繞庫排砂效益分析
(一) 針對國內、外或中國大陸相關繞庫排砂工法進行蒐集整理
蒐集整理國內、外與中國大陸相關繞庫排砂工法。
(二) 分析探討青草湖減淤與排砂方案（含繞庫排砂）於各重現期流量條件下，對客雅溪上、下游河道之沖淤變化與防洪安全影響
本計畫規劃青草湖減淤與排砂方案（含繞庫排砂），並針對可能方案（沉砂區清淤）進行模擬，探討可能方案對客雅溪上、下游河道之沖淤變化與防洪安全影響。
(三) 青草湖附近的地籍圖資料蒐集整理
蒐集整理青草湖附近的地籍圖資料，供青草湖減淤與排砂方案（含繞庫排砂）之土地取得經費概估。
(四) 針對各種青草湖減淤與排砂方案（含繞庫排砂），進行初步工程佈置規劃及經費估算
本計畫針對各種青草湖減淤與排砂方案（含繞庫排砂），進行初步工程佈置規劃及經費估算。
(五) 青草湖減淤與排砂方案（含繞庫排砂）應用於青草湖之效益分析
本計畫針對各青草湖減淤與排砂方案（含繞庫排砂），考量各方案之工程與清淤費用、經濟效益、方案之優缺點、設置可行性，探討各方案之優先順序。
The Green Grass Lake reservoir is located on the midstream of the Ke-ya river in Hsinchu City for early irrigation and tourism functions of both the reservoir and the well-known scenic spot in Hsinchu area. Upstream of the reservoir area are the property of the valley topography, basin strata exposed the Pliocene Cholan formation and Pleistocene alluvium, soft soil vulnerable to erosion, flood could easily lead to the earthwork loss and flow into the Green Grass Lake, so storage capacity each year dropped, resulting in loss of function of flood control and irrigation, retaining only the current tourism and recreation function by Hsinchu City Government is responsible for managing.
The purpose of this plan is through evaluation of floating debris intercept scheme and feasibility of setting position, to analyze whether there are suitable for intercept scheme and position to reduce floating debris (such as: bamboo) into the Green Grass Lake. In addition, this plan analysis sediment bypassing benefit which applied to Green Grass Lake to assess the feasibility of reducing sediment flow into the Green Grass Lake for sediment bypassing scheme. The work items if this plan are summarized as follows:
I. Floating debris intercept scheme evaluation on Ke-ya river upstream
(1) Survey and collection existing fluvial geomorphology data on Green Grass Lake Upstream
Investigated and collected aspect, slope, elevation and cross section data with 2005, 2008 and 2012 in planning area.
(2) Survey and collection geological data around the Green Grass Lake
Investigated and collected soil, geological structure and fault data of Ke-ya river and Green Grass Lake.
(3) Collection river floating debris intercept method (such as: bamboo)
Collected river floating debris intercept method which could be divided into a grid interception facilities (including full-face, submerged dam type and simple grill) and trash cable。
(4) Appropriate selected position and analysis of floating debris intercept method on the Ke-ya River upstream
This plan considered of floating debris of main source, width of river, flooding potential disaster area, stratigraphy and geological conditions of setting location, ecological conservation and other factors, planned preliminary schemes of setting location of floating debris intercept method.
(5) Water level and conveyance capability impact analysis for each return period discharging after setting floating debris intercept method on Ke-ya river upstream
This plan utilized HEC-RAS mode to simulate floating debris intercept scheme, and analyzed water level and conveyance capability impact for each return period discharging on Ke-ya river upstream.
II. Sediment bypassing benefit analysis of Green Grass Lake
(1) Collection domestic and foreign or China related sediment bypassing method
Collected domestic and foreign or China related sediment bypassing method.
(2) Analysis the impact of erosion and flood safety of each sediment reduction and emission scheme (including sediment bypassing) of Green Grass Lake for each return period discharging on Ke-ya River upstream and downstream
Sediment reduction and emission schemes (including sediment bypassing) of Green Grass Lake and simulate possible solutions (sand dredging area) were planned in this plan, and analyzed impact of erosion and flood safety for each return period discharging on Ke-ya River upstream and downstream .
(3) Collection the cadastral map information nearby Green Grass Lake
This plan collected the cadastral map information nearby Green Grass Lake to provide land acquisition cost estimation for sediment reduction and emission schemes (including sediment bypassing) of Green Grass Lake.
(4) Preliminary engineering layout planning and cost estimation for each sediment reduction and emission scheme (including sediment bypassing) of Green Grass Lake
Preliminary engineering layout and estimate cost for each sediment reduction and emission scheme (including sediment bypassing) of Green Grass Lake were planned in this plan.
(5) Sediment reduction and emission schemes (including sediment bypassing) benefit analysis of Green Grass Lake
Engineering and dredging cost, economic benefits, advantages and disadvantages, the feasibility of setting to explore the different scheme priorities for each sediment reduction and emission scheme (including sediment bypassing) were considered in this plan