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Study on Using Hydraulic and Meandering Characteristics of River Corridor Evaluating Aquatic Habitat Restoration Suitability
River channel pattern
River corridor is rich in wildlife resources and forms diversity in aquatic habitats. Because of the rapid expansion of economic activities, a tremendous amount of behaviors of aquatic wildlife including resting, breeding and feeding have followed. A fine aquatic habitat environment is necessary in order to maintain a sustainable river ecosystem. However, efforts of restoration are complicated by factors such as “water quality”, “river morphology”,“food chain of ecosystem”,“human activities”, and so on, which impact the aquatic habitat environment. The proper habitat is so scarce that it is necessary to return the original environmental condition by means of artificial methods to preserve the vitality of species.
Because the most suitable hydraulic factors of aquatic are not similar in the river,we can't use a function to set a standardization. If we think about other factors such as water quality and water temperature…etc., it must be even more difficult to distinguish the levels of habitat quality. While we proceed to conduct overall investigation on suitability of aquatic habitat, it may require great amount of budget, manpower, and time. In order to achieve the concrete goal of river restoration planning, it is necessary to reduce wrong attempts through a reasonable estimation to sift out proper locations.
This study bases on the fundamental characteristics in different river types (meandering, straight and braided) to select a suitable field for habitat restoration, and utilize the original hydrology and topographic data to estimate the “hydraulic radius”, “mean velocity”, “water surface width”, “submerge velocity and area”, “river ecological base-flow”, “habitat area”, “slope and sinuosity”…and so on. By assessing the present condition of river environment, we can get a suitable region for restoration. It can be regarded as a rapid and easy way to save budget. The suitable region for restoration still needs the assistance of ecological investigation, water quality investigation, and landscape planning…etc., to estimate more objective effects. Below is the consequence of the analyses.
In meandering river
According to the relationship between “sinuosity”, “slope”,“fish community” and “shear stress”, we can adopt a suitable reach for restoration.
Taking the example of Maolo stream and its tributaries of Pinlin stream and Chainpin stream, I valuated the sinuosity and slope in each reach and assessed their restoration potential with the aid of “hydraulic routing”.
Below is regarded as the suitable reach to initiate habitat restoration.
1. Pinlin stream (a) between section 30~34 (b) between section 37.2~40 (c) between section 42.2~43.2 (d) between section 45.1~47
2. Chainpin stream (e) between section 7~9 (f) between section 16~17 (g) between section 16.2~17.2 (h) between section 22.1~25.2
In straight river
When the sensitivity of sinuosity is no longer obvious, the task needs to depend on other factors such as “velocity”; “depth”; “water surface width”, and so on, and with progress analyzing done by statistical manner.
First, we divide the “mean depth”, “mean velocity”, and “water surface width” into several levels separately by their quantity. The purpose is to quantify the suitability of habitat so that we can statistically analyze them give a weighted value to apparent the importance of some factors, and analyze by different weighted value. The finally goal is to estimate the most suitable habitat, so it is better to base on our demands when deciding a manner and weight value in dividing levels.
Taking the example of Fatze stream. The consequence in whole reach as section 4,11,15,32 are the best regions of restoration, and sections 0,6,17,25 are second best.
In braided river
When the river becomes braided, the variation of “velocity”; “depth”; “water surface width” becomes slow, too. We must adopt another set of index factors such as “drowned time”, “drowned depth”, and “drowned area” to obtain more representative consequence, and consult sediment transport ability and make sure of the gap condition of braided river with aerial photo map (scale=1/5000), which benefit determining the suitability of habitat.
Here downstream reach of Wu River is taken as an example. The result in sections 15 and 31 are the best regions of restoration, and section 16 and 17 are second best. In general, between sections 17~25 is the reach where the braiding is obvious, in riparian zone; water surfaces, land and bars are mixed and alternating.Therefore, we can stretch the best reach of restoration toward upstream to section 25, to include section 15~25.|
摘 要 河川廊道(river corridor)蘊育著各式各樣的生物而形成多樣化的河川生態系。由於人類經濟快速發展導致水生生物無論在棲息、繁衍暨覓食等行為習性均隨之產生重大變化。為維繫河川生態之綿延不絕，良好的棲地環境實為必要條件，然其影響因素相當複雜，如水質、河川形態、生態體系之食物鏈、人類活動…等，因此適宜之棲地不可多得，須藉由人為方式回歸其原本之需求環境，以延續河川生物種源之生命力。 緣以河川中各種水生生物之最適宜水理因子均不相同，吾人無法以一數學函數定出標準值，倘再將其他影響因子如水質、水溫等併入考量，更難以釐清棲地之優劣等級，而欲進行詳盡之棲地適宜性及生態調查等必須耗費大量經費、人力及時間。因此，為使河川復育計畫達具體成效，應減少錯誤的嘗試並透過合理之研判以篩選出適宜復育地點。 本研究藉由探討不同河川型態(蜿蜒；直線；辮狀)之基本特性，做為選定棲地復育場所之考量依據。利用初始之水文、地形資料推算出水力半徑、平均流速、水面寬、坡度、淹水速度與面積、生態基流量、棲地面積，坡度及蜿蜒度等，再針對河川環境現況評估而得出適宜復育區域，不失為一種快速便捷且節省經費之方法。但分析出之適宜復育區域尚需再輔之以生態調查、水質調查、景觀布置…等諸工作事項，以求得更客觀之結果。各種型態之河川分析原則及結果分別如下: 一、蜿蜒河川(meandering river) 蜿蜒河川中乃依據各河段之蜿蜒度、坡度、魚類群聚度等之相關性及河道剪力，比較其優劣得失並藉以選定可供復育河段。 本研究以烏溪水系之貓羅溪及其支流平林溪、樟平溪為例，逐一求取各河段之蜿蜒度(sinuosity)及坡度，再輔之以水理演算評估之。分析結果以如下(a)~(g)各河段可視為適合進行棲地復育工作之河段。 1.平林溪(a)斷面30~34間(b)斷面37.2~40間(c)斷面42.2~43.2間(d)斷面45.1~47間 2.樟平溪(e)斷面7~9間(f)斷面16~17間(g)斷面16.2~17.2間(h)斷面22.1~25.2間 二、直線河川(straight river) 在直線河道中「蜿蜒度」之敏感性不再明顯，因此需另尋求一敏感度較高之水理與地形因子如「流速」、「水深」、「水面寬」等，再輔之以統計方式配賦權值進行分析。 首先分別將平均水深、平均流速及水面寬等依大小不同分級計分，其目的乃在於將棲地之適宜度予以量化，便於統計分析，再賦予加權值以突顯某項因子之重要性，俾分別以不同權值分析之。因最終目標乃在於評估取得最適宜之棲地，故儘量以需求性為導向，訂出滿足自己要求之分級計分方式及權值進行棲地適宜性之推估。 本研究以烏溪支流筏子溪為例進行分析。分析結果在全河中段以斷面4, 11, 15, 32等為最適合復育區，斷面0, 6, 17, 25等次之。 三、辮狀河川(braided river) 當河道呈辮狀分岐，流速、水深、水面寬等因子之變化開始顯現遲緩，必需另擇指標因子如「淹水時間」、「淹水深度」及「淹水面積」以求得更具代表性之結果。並參考輸砂能力，再以航照圖(1/5000)查對河段內之辮狀分岐情況，俾輔助判斷棲地之適宜性。 本研究以烏溪本流下游段為例進行分析，分析結果以斷面15及斷面31附近皆為較佳。斷面16及斷面17為次佳地點。倘若以整體而言，因斷面17~25間為辮狀河段較顯著區，其水域、砂洲、陸域間交互依存，可將復育河段向上游延伸至斷面25，即斷面15~25間區域。
|Appears in Collections:||水土保持學系|
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