JP3963430B2

JP3963430B2 - Marine wetland breeding method and coastal wetland

Info

Publication number: JP3963430B2
Application number: JP2002037347A
Authority: JP
Inventors: 毅池谷; 昌宏田中; 成三上野; 百合子高山
Original assignee: Taisei Corp; Kajima Corp
Current assignee: Taisei Corp; Kajima Corp
Priority date: 2002-02-14
Filing date: 2002-02-14
Publication date: 2007-08-22
Anticipated expiration: 2022-02-14
Also published as: JP2003239241A

Description

【０００１】
【発明の属する技術分野】
本発明は臨海湿地の育成方法及び臨海湿地に関し、とくに多様な生物が生息できる臨海湿地を育成する方法及び臨海湿地に関する。
【０００２】
【従来の技術】
多くの臨海域において、図８（Ａ）に示すように、海水11による浸食から岸10を保護するため、コンクリート擁壁等の直立護岸８が建設されている。しかし、直立護岸８による生態系破壊の問題点が指摘され、最近では直立護岸８により直線化された海岸線を勾配のある自然な海岸線に再生し、衰弱しつつある自然の生態系を健全なものに蘇らせることが提案されている（例えば、２１世紀『環の国』づくり会議報告書）。具体的には、同図に示すように、自然の生態系を蘇らせるために必要な干潟33や藻場35等の生物生息環境の保全又は再生が積極的に推進されている。また、特定の生物（例えばアサリ、カニ類、ゴカイ類、アマモ等）の生息に適する干潟33や藻場35の材料（底質土）や構造の研究・開発も進められている。
【０００３】
【発明が解決しようとする課題】
しかし、従来の保全又は再生した干潟33や藻場35では、特定の生物をある程度生息させ得ることは確認されているが、自然の海岸線に見られる種類・量が豊富な生態系を蘇らせることが難しい問題点がある。この理由の１つは、自然の海岸線には単に物理的な勾配が存在するだけでなく、図８（Ｂ）にようにヨシ等の湿生植物３の生息環境２（以下、ヨシ原２ということがある。）・干潟生物５の生息環境である干潟４・藻類７の生息環境である藻場６等の複数の生物生息環境が空間的に連接ないし隣接して存在しているのに対し、保全又は再生した干潟33や藻場35では自然の一部の構成要素が単独で存在するに過ぎないことにある。例えば、自然の海岸線で生息する生物のなかには、ライフスタイル（餌場、産卵場、休息場等）や生活史（浮遊幼生期、稚児期、成体期等）に応じて複数の生息環境を必要とするものがある。このような生物を含む多様な生物が生息できる海岸線を保全又は再生するためには、ヨシ原２・干潟４・藻場６等の複数の生物生息環境を空間的に連ねて一体的に保全又は再生する必要がある。
【０００４】
そこで本発明の目的は、ヨシ原と干潟とを空間的に連ねて保全又は再生できる臨海湿地の育成方法及び臨海湿地を提供することにある。
【０００５】
【課題を解決するための手段】
本発明者は、自然の臨海湿地では後背地から淡水が地下水として供給されていることに注目した。臨海湿地で淡水と海水とが交じり合うことにより汽水域が形成され、その汽水域がヨシ原２となっている。汽水域のヨシ原２は、カニ類やそれ等を餌とする生態系上位の鳥類の生息場所となっており、有機物・窒素・リン等の水質浄化能力も高いことが報告されている。ヨシ原２を育成するためには汽水域を形成することが必要である。
【０００６】
更に本発明者は、ヨシ原２に隣接して干潟４を有する自然の臨海湿地の調査に基づき、ヨシ原２の地下水位及び地下水中の塩分（以下、単に塩分ということがある。）が干潟に近づくに応じて連続的に変化していることを見出した。図７は自然の臨海湿地における地下水位及び塩分等の調査結果を示し、同図の各グラフの横軸は水際線（汀線）から調査地点までの距離（即ち、干潟と調査地点との間の距離）を示す。同図（Ａ）はヨシ原２の代表生物であるヨシのバイオマス（生物体量）の変化、同図（Ｂ）はヨシ原２の地盤レベル及び地下水レベルの変化、同図（Ｃ）はヨシ原２の塩分（実用塩分）の変化を表わす。
【０００７】
図７（Ａ）のグラフから、ヨシ原２におけるヨシのバイオマスは、汀線近傍を除き、汀線からの距離に応じて減少していることが分かる。同図（Ｂ）に示すように汀線からの距離に応じて地下水面の深さ（地盤レベルと地下水レベルとの差）が増大しているので、ヨシのバイオマスの減少要因は地下水面深さの増大であることが分かる。また、同図（Ｃ）に示すように汀線近傍で塩分が非常に高いので、汀線近傍におけるヨシのバイオマスの減少要因は塩分の上昇であることが分かる。即ち、ヨシ原２の海側境界は塩分により、陸側境界は土壌の水分量を示す地下水面深さにより規定されている。
【０００８】
自然のヨシ原２と干潟４との境界では、ヨシ原２の湿生植物３が徐々に減少すると共に塩分を必要とする干潟生物５が徐々に増加しており、境界線が必ずしも明確ではない。このようなヨシ原２と干潟４という２つの生物生息環境の空間的な連接ないし隣接を可能にする要因は、図７（Ｃ）のような塩分の連続的な変化にあると考えられる。このような塩分の連続的な変化は、同図（Ｂ）のような地下水位の連続的な変化により形成されたものである。臨海湿地を育成する際に、前記塩分の連続的な変化が生じるように地下水位を形成すれば、ヨシ原２と干潟４とを空間的に連ねて育成することが期待できる。本発明はこの知見に基づく研究開発の結果、完成に至ったものである。
【０００９】
図１の実施例を参照するに、本発明の臨海湿地の育成方法は、岸10から海底へ緩やかに下降傾斜する沿岸土13の汀線から距離Ｌ（同図（Ｂ）参照）を隔てた岸側に沿って透水壁 22 を介して汀線以上の水位高さΔＨ（同図（Ｂ参照）の淡水流路 21 を設け、その淡水流路 21 に沿岸土 13 の吸い込みを防ぐフィルター材 28 を設置し、透水壁 22 により、沿岸土 13 の透水係数ｋに応じて淡水流路 21 の水位高さΔＨから汀線近傍に連なる動水勾配（ΔＨ／Ｌ）の地下水位15が形成される流速ｕ（＝ｋ・ΔＨ／Ｌ）又は流量Ｑで淡水 12 を沿岸土 13 中に供給してなるものである。淡水流路 21 の水位高さΔＨを地下水位15が湿生植物３の生息に適する深さとなる高さとし、沿岸土13を湿生植物３に適する粒度の砂質土とすることが望ましい。
【００１０】
また図１及び図４の実施例を参照するに、本発明の臨海湿地は、岸10から海底まで緩やかに下降傾斜させて客土した所定透水係数ｋの沿岸土13、沿岸土13の汀線から所定距離Ｌ（図１（Ｂ）参照）隔てた岸側に沿って透水壁 22 を介して設けた汀線以上の所定水位高さΔＨ（同図（Ｂ参照）の淡水流路 21 、及び淡水流路 21 に設置された沿岸土 13 の吸い込みを防ぐフィルター材 28を備え、透水壁 22 により、沿岸土 13 の透水係数ｋに応じて淡水流路 21 の水位高さΔＨから汀線近傍に連なる動水勾配（ΔＨ／Ｌ）の地下水位15が形成される流速ｕ（＝ｋ・ΔＨ／Ｌ）又は流量Ｑで淡水 12 を沿岸土 13 中に供給してなるものである。
【００１１】
好ましくは、図１（Ａ）に示すように、沿岸土13上の満潮時汀線と干潮時汀線との間の部位に干潟底質土18を客土する。干潟底質土18は、スナガニ類、貝類及び／又は多毛類の生息に適する粒度のものとすることができる。更に好ましくは、沿岸土13上の干潮時汀線より低い部位に藻類７の生息に適する藻場底質土19を客土する。ここに満潮時汀線とは平均満潮線HWLと沿岸土13との交線、干潮時汀線とは平均干潮線LWLと沿岸土13との交線である。
【００１２】
【発明の実施の形態】
図１及び図４は、岸10から沖へ向かう方向に緩やかに下降傾斜する臨海湿地を育成する本発明の実施例を示す。本発明による臨海湿地の育成対象の一例は、図４に示すように潜堤32上に人工的に客土した沿岸土13である。但し、本発明は人工的に造成した沿岸土13への適用に限定されず、例えば図１に示すように生態系が衰弱した天然又は人工の沿岸土13に本発明を適用して臨海湿地の保全・再生に用いることができる。
【００１３】
臨海湿地を育成するため、沿岸土13に汀線以上の高さで淡水12を供給する淡水供給設備20を設ける。図示例の淡水供給設備20は、沿岸土13の岸10側に沿って透水壁22を介して設けた淡水流路21を有し、淡水流路21から透水壁22経由で淡水12を沿岸土13に供給する。例えば河川水や地下水、雨水等の淡水12をポンプ等の淡水導入手段30によって淡水流路21へ導き、淡水流路21の水位を汀線以上の所要水位に保ち、汀線以上の高さから淡水12を供給する（図４参照）。透水壁22は後述するように所要流速又は流量で淡水12を通すものであれば足り、例えば透水コンクリート壁、適当な孔を設けた壁体、石積壁等とすることができる。また、淡水流路21を有孔管により構成し、その有孔管の周壁を透水壁22としてもよい。
【００１４】
沿岸土13が砂質土、シルト、粘土等の細粒径の土で構成されている場合は、透水壁22を介して沿岸土13が淡水流路21中に漏れ出ないように、淡水流路21に沿岸土13の吸い込みを防ぐフィルター材28を設置することが望ましい（図４参照）。フィルター材28としては、粒度を調整した砂礫材、防砂シート、フィルターユニット（砕石詰網袋工）等を用いることができる。例えば、フィルター材28の内部に有孔管を敷設して淡水流路21とする。また、フィルター材28の上部から淡水12を供給して淡水流路21とすることができる。
【００１５】
淡水流路21に導入された淡水12の一部分は透水壁22を通って沿岸土13中に供給される。沿岸土13の汀線以下の部分には海水11が滞留しているが、淡水12は海水11よりも比重が小さいので、供給された淡水12は海水11上に浮いて汀線以上の地下水位15を形成する。但し、本発明における淡水供給設備20は図示例に限定されず、汀線以上の高さから淡水12を供給できるものであれば足り、例えば沿岸土13の表面への散水により淡水12を供給するものとしてもよい。
【００１６】
淡水流路21の淡水12を所要水位に保つため、図４では淡水流路21に越流堰26付き排水ピット25を設け、淡水流路21に導入された淡水12のうち余剰水を越流堰26により排水ピット25内へ導き、排水路27を通じて海域に排出している。但し、淡水位の保持方法は図示例に限定されず、例えば淡水導入量の調整により所要の淡水位を保持してもよい。
【００１７】
淡水流路21の底部が汀線以下である場合は、淡水12よりも比重が大きい海水11が淡水流路21に流れ込むおそれがあるので、図４（Ｂ）及び（Ｃ）に示すように透水壁22の汀線以上の部位のみを透水部23とし、汀線以下の部位を非透水部24とすることが好ましい。また、図１のように淡水流路21の底部を満潮時汀線より高くして淡水流路21への海水11の流入を防ぐことも可能である。
【００１８】
沿岸土13にヨシやナガミノオニシバ、クサヨシ、アイアシ、ギシギシ、フクド、ウラギク、シオクグ（カヤツリグサ科）、ホウキギク等の湿生植物３を生息させるため、好ましくは沿岸土13を湿生植物３に適する粒度の砂質土とするか又は沿岸土13上の汀線以上の部位に湿生植物３に適する粒度の砂質土を客土する。例えばヨシの生息には粒径0.2mm程度の土壌が好ましく、粒径が大き過ぎる礫や岩石、粒径が小さ過ぎるシルトや粘土質では不適切であるとの報告がある。このため、沿岸土13上にヨシを生息させる場合は、沿岸土13上の汀線以上の部位に粒径0.02〜0.3mm程度の砂質土を客土する。また、ヨシの生育には50〜60cmの土壌厚さが必要であるとの報告があるので、例えば沿岸土13上に中央粒径（通過質量百分率50％の粒径）0.02〜0.3mm程度の砂質土を50〜60cmの厚さで客土することが望ましい。
【００１９】
また、沿岸土13中の地下水位15を湿生植物３の生息に適する深さとすることが望ましい。本発明者は、前述した自然の臨海湿地における調査から、地下水面深さ（地盤レベルと地下水レベルとの差）ｄが15cm以上になるとヨシのバイオマスが減少し、35cm以上になると著しく減少することを見出した。このため、ヨシを生息させる場合は、沿岸土13中に地下水面深さｄを35cm以下、好ましくは15cm以下とする。このような地下水位15を形成するためには、例えば図１（Ｂ）のように、潮線よりH₁だけ高い部位に淡水流路21を設け、淡水流路21内の淡水位、即ち淡水11の水頭を潮線よりΔＨ（＝H₁−ｄ）だけ高く保つ。
【００２０】
更に、沿岸土13に湿生植物３を生息させるため、前記適切な地下水位15が広い範囲で確保できるように沿岸土13の汀線以上の勾配を定めることができる。図１では淡水流路21を汀線から距離Ｌだけ離して設け、沿岸土13の緩やかな勾配に応じて、地下水位15を淡水流路21から汀線近傍まで緩やかに下降させている。この場合、満潮時における地下水14の動水勾配ｉは図１（Ｂ）に示すようにΔＨ／Ｌとなる。他方、前述した沿岸土13の粒度から沿岸土13の透水係数ｋを定めることができる。土中の地下水14の動きは下記(1)式又は(2)式で示すダルシーの法則に従うことが知られており、透水係数ｋの沿岸土13中に動水勾配ｉの地下水位15を形成するためには、沿岸土13に対して(1)式の流速ｕ又は(2)式の流量Ｑで淡水12を供給するように透水壁22を設計すればよい。なお、透水の流量Ｑは透水の流速ｕと透水壁22の透水孔の断面積Ａとの積で表わされる。
【００２１】
【数１】
ｕ＝ｋｉ＝ｋ・（ΔＨ／Ｌ） …………………………………………………(1)
Ｑ＝Ａｕ＝Ａ・ｋｉ＝Ａ・ｋ・（ΔＨ／Ｌ） ………………………………(2)
【００２２】
上述した流速ｕ又は流量Ｑで淡水12を透水係数ｋの沿岸土13中に供給すれば、図１（Ｂ）に示すように淡水供給部位から汀線近傍に連なる地下水位15を形成できる。即ち、図７を参照して説明したように、干潟に近づくに応じて地下水面深さが徐々に減少する自然の臨海湿地と同様な地下水位15を沿岸土13中に形成できる。また、このように地下水面深さが連続的に変化する地下水位15を形成すれば、沿岸土13中に淡水から海水に至る塩分の連続的な変化を作り出すことができる。例えば、ヨシは塩分10PSU以上で発芽率が低下し、生息可能限界値は塩分20PSU以上であるとの報告がある。このため、塩分が20PSU以下、好ましくは10PSU以下となる広い範囲が確保できるように地下水位15を形成することにより、汀線近傍域までヨシを生息させることが可能となる。
【００２３】
好ましくは、沿岸土13上の満潮時汀線と干潮時汀線との間の部位に干潟底質土18を客土することにより、アサリ、カニ類、ゴカイ類等の干潟生物５の生息を図ることができる。本発明者の調査によれば、例えばスナガニ類の生息可能な塩分は0.2PSU以上であり、稚ガニの生息には５PSU以上が望ましい。本発明は、沿岸土13に供給した淡水12をそのまま干潟底質土18に流入させるのではなく、汀線への接近に応じて塩分を高めた上で流入させるので、干潟底質土18の全域をスナガニ類等の干潟生物５の生息環境とすることができる。また、干潮時には図１（Ｃ）に示すように干潟底質土18の表面近傍に地下水位15が形成されるが、この場合も地下水14の塩分が海水と同程度であるため、干潟生物５の生息環境に対する地下水14の流入の影響を最小限に抑えることができる。
【００２４】
本発明は、沿岸土13中に汀線への接近に応じて塩分が徐々に増加する地下水位15を形成するので、汽水域の湿生植物３と海水域の干潟生物５とが共に生息する境界域を作り出すことができ、ヨシ原２と干潟４という２つの生物生息環境を空間的に連ねて育成できる。また、干潮時においても地下水位15が地表近傍に維持されるので、満潮時汀線と干潮時汀線との間の部位を干潟生物５の生息に適する湿潤状態に保つことができる。なお、本発明によればヨシ原２と干潟４とを連接ないし隣接させて育成可能であるが、必要に応じて両者の間に緩衝帯や段差等を設けてもよい。
【００２５】
こうして本発明の目的である「ヨシ原と干潟とを空間的に連ねて保全又は再生できる臨海湿地の育成方法及び臨海湿地」の提供を達成できる。
【００２６】
好ましくは、図１（Ａ）に示すように、沿岸土13上の干潮時汀線より低い部位に適当な水深で藻類７の生息に適する藻場底質土19を客土する。藻場底質土19を客土することにより、沿岸土13上にヨシ原２・干潟４・藻場６という３つの生物生息環境を空間的に連ねて一体的に育成することが可能となり、自然に極めて近い健全な海岸線の育成が期待できる。
【００２７】
なお、極度に有機汚染された土壌ではヨシ原２や干潟４を育成できないが、ヨシ原２や干潟４の育成にはある程度の有機物が必要である。例えばヨシの場合は、土壌中の有機物が減少するにつれてヨシが衰退し水コケ類に遷移するといわれている。このため、例えば適当な有機物濃度の淡水12（例えば中水、排水処理後の放流水等）を沿岸土13に供給し、沿岸土13、底質土18、19を湿生植物３や干潟生物５の生息に適する強熱減量に調整することが好ましい。更に好ましくは、淡水12中に湿生植物３、干潟生物５及び／又は藻類７の栄養物質を溶存させ、それら栄養物質を沿岸土13、底質土18、19に供給する。なお、栄養物質として微量要素も挙げられる。
【００２８】
【実施例】
図２は、図１（Ｂ）よりも高い地下水位15を形成した本発明の他の実施例を示す。本発明は、地下水位15により沿岸土13中に汀線からの距離に応じて変化する図７（Ｃ）のような塩分濃度勾配を形成するが、その塩分勾配は供給する淡水12の水量等に応じて変化し得る。沿岸土13上に湿生植物３の広い生息範囲を確保するためには、汀線近傍域まで湿生植物３が生息可能な低い塩分であることが望ましい。しかし、例えば淡水量が少ない場合は、汀線近傍域の塩分が湿生植物３の生息可能範囲より高くなる場合も起こり得る。
【００２９】
図２では、地下水位15の調節により、沿岸土13中の淡水から塩水に至る塩分勾配を湿生植物３の生息に適する範囲としている。すなわち、淡水供給部位から汀線よりδだけ高い部位に連なる地下水位15を形成することにより、汀線近傍域における塩分を図１（Ｂ）の場合に比して低く維持し、淡水量が少ない場合でも汀線近傍域の塩分を湿生植物３が生息可能な範囲内とすることができる。
【００３０】
また図３は、沿岸土13中に地下水位15を所要深さとするための不透水層17a、17b、17cを設けた本発明の実施例を示す。上述したように沿岸土13の透水係数ｋは粒度等から定まるが、沿岸土13の粒度によっては湿生植物３の生息に適する深さの地下水位15とすることが難しい場合も起こり得る。このような場合は、沿岸土13中に適当な不透水層17を設けて地下水位15を調整することができる。なお、図示例では沿岸土13中に３層の不透水層17a、17b、17cをそれぞれ鉛直方向に設けているが、不透水層17の数や配置は図示例に限定されない。例えば水平又は所要勾配の不透水層17を設けて沿岸土13中の地下水位15を調整することができる。
【００３１】
本発明は、図５に示すような直立護岸８により直線化された海岸線の保全・再生に効果的に利用できる。図５の実施例では、沿岸土13を岸10から沖へ向かう方向に緩やかに下降傾斜させて客土し、沿岸土13上の満潮時汀線と干潮時汀線との間の部位、及び干潮時汀線より低い部位にそれぞれ干潟底質土18、及び藻場底質土19を客土することにより、岸10から沖へ向かう方向に沿って湿生植物３、干潟生物５、藻類７の生息環境を空間的に連ねて育成している。ヨシ原２・干潟４・藻場６を一体的に育成することにより、自然に近い種類・量が共に豊富な生態系の蘇生が期待できる。また同図では、護岸８に淡水導入孔34を穿ち（即ち、護岸８を透水壁構造とし）、導入孔34を介して護岸８の岸側の淡水流路21から海側の沿岸土13へ淡水12を供給している。但し、淡水12の供給方法は図示例に限定されない。
【００３２】
但し、図５のようにヨシ原２・干潟４・藻場６を一体的に育成する場合は、岸沖方向の距離が問題となる場合がある。干潟底質土18は泥質やシルトを含むので、干潟底質土18の流出を避けるために干潟４を緩やかな勾配とする必要がある。また、ヨシ原２も適正な地下水位15を広い範囲で確保するために緩やかな勾配が必要である。更に、沖の海底に藻場６を育成するためには、更に長い岸沖方向の距離が必要となる。護岸８の海側前面の水域が狭い場合は、図５の方法では臨海湿地の育成が難しい場合がある。また、臨海湿地全体の規模が非常に大きくなるので、人工構造物としての実現性が困難となる場合もある。
【００３３】
図６の実施例は、緩やかな勾配の広い臨海湿地を造成するため、岸10から沖へ向かう方向に代えて、ヨシ原２・干潟４・藻場６を岸10に沿って連ねて一体的に育成する実施例を示す。同図（Ａ）及び（Ｂ）では、護岸８に沿って海側に不連続の消波壁36を設け、護岸８と消波壁36と間に沿岸土13を、護岸８と平行に且つ消波壁36の不連続部37が干潮時汀線より低くなるように緩やかに下降傾斜させて客土し、消波壁36の不連続部37から沿岸土13上に海水11を浸入させ、湿生植物３と干潟生物５と藻類７とを護岸８に沿って生育させている。このように岸10に沿ってヨシ原２・干潟４・藻場６を再生すれば、既存の護岸前面の水域が狭い場合でも、護岸８の前面に適当な勾配の広い臨海湿地を比較的小規模な人工構造物として造成することできる。
【００３４】
また、図６（Ｃ）に示すように、護岸８の前面ではなく、護岸８の一部分を開削した裏側（岸10側）に沿岸土13を護岸８と平行に且つ開削部39が干潮時汀線より低くなるように緩やかに下降傾斜させて客土し、開削部39から沿岸土13上に海水11を浸入させることにより、ヨシ原２・干潟４・藻場６を護岸８に沿って一体的に育成することもできる。
【００３５】
【発明の効果】
以上説明したように、本発明による臨海湿地の育成方法及び臨海湿地は、岸から海底へ緩やかに下降傾斜する沿岸土に汀線以上の高さから淡水を供給し、淡水供給部位から汀線近傍に連なる地下水位を形成するので、次の顕著な効果を奏する。
【００３６】
（イ）沿岸土中に淡水から塩水に至る所要塩分勾配を形成することができ、ヨシ原と干潟とを空間的に連ねて一体的に育成できる。
（ロ）沿岸土に形成した地下水の塩分を高めつつ汀線近傍に流入させるので、干潟生物に対する影響を最小限に抑えつつ、干潟を湿潤状態に保つことができる。
（ハ）ヨシ原と干潟という複数の生物生息環境を空間的に連ねて育成できるので、種類・量が豊富な自然の生態系を作ることが期待できる。
（ニ）満潮時汀線と干潮時汀線との間の部位に干潟底質土を客土することにより、自然の干潟に一層近い臨海湿地が育成できる。
（ホ）更に干潮時汀線より低い部位に藻場底質土を客土することにより、ヨシ原・干潟・藻場を空間的に連ねて一体的に再生し、自然に極めて近い海岸線の育成が期待できる。
（ヘ）直立護岸により直線化された既存の水際線を勾配のある自然な海岸線に育成する自然再生型の海岸造成事業への寄与が期待できる。
（ト）岸に沿ってヨシ原・干潟・藻場を育成することにより、狭い水域でも緩やかな勾配の広い臨海湿地を育成できる。
【図面の簡単な説明】
【図１】は、本発明の一実施例の説明図である。
【図２】は、本発明の他の実施例の説明図である。
【図３】は、不透水層を設けた本発明の更に他の実施例の説明図である。
【図４】は、本発明で用いる淡水供給設備の一実施例の説明図であり、（Ａ）は平面図、（Ｂ）、（Ｃ）及び（Ｄ）はそれぞれ平面図（Ａ）のＢ−Ｂ、Ｃ−Ｃ及びＤ−Ｄにおける断面図である。
【図５】は、ヨシ原・干潟・藻場を岸から沖へ向かう方向に沿って連ねて育成した本発明の実施例の説明図である。
【図６】は、ヨシ原・干潟・藻場を岸に沿って連ねて育成した本発明の他の実施例の説明図であり、（Ｂ）及び（Ｃ）はそれぞれ平面図の一例、（Ａ）は平面図（Ｂ）又は（Ｃ）のＡ−Ａにおける断面図である。
【図７】は、ヨシ原におけるバイオマス、地下水レベル、塩分濃度の変化を示すグラフである。
【図８】は、従来の直立護岸を設けた海岸線（Ａ）と自然の海岸線（Ｂ）との相異を表わす説明図である。
【符号の説明】
１…臨海湿地２…ヨシ原
３…湿生植物４…干潟
５…干潟生物６…藻場
７…藻類８…直立護岸
９…埋立地 10…岸
11…海水 12…淡水
13…沿岸土 14…地下水
15…地下水位
17…不透水層 18…干潟底質土
19…藻場底質土 20…淡水供給設備
21…淡水流路 22…透水壁
23…透水部 24…不透水部
25…排水ピット 26…越流堰
27…排水路 28…フィルター材
30…淡水導入手段 32…潜堤
33…干潟 34…淡水導入孔
35…藻場 36…消波壁
37…不連続部 39…開削部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a coastal wetland breeding method and a coastal wetland, and more particularly to a method and a coastal wetland for breeding a coastal wetland where various organisms can live.
[0002]
[Prior art]
In many coastal areas, as shown in FIG. 8 (A), an upright revetment 8 such as a concrete retaining wall is constructed to protect the shore 10 from erosion by seawater 11. However, the problem of ecosystem destruction by the upright revetment 8 has been pointed out, and recently, the coastline straightened by the upright revetment 8 has been restored to a natural slopeline, and the natural ecosystem that has been deteriorating is healthy. (For example, the report of the 21st century “Nationwide” conference). Specifically, as shown in the figure, the conservation or regeneration of biological habitat environments such as tidal flats 33 and seaweed beds 35 necessary for reviving natural ecosystems is being actively promoted. In addition, research and development of materials (bottom soil) and structure of the tidal flat 33 and seaweed bed 35 suitable for the habitat of specific organisms (for example, clams, crabs, sandworms, sea bream, etc.) are also underway.
[0003]
[Problems to be solved by the invention]
However, it has been confirmed that some of the existing organisms can be inhabited to some extent in the traditionally preserved and reclaimed tidal flats 33 and seaweed beds 35, but it is necessary to revive the ecosystems rich in types and quantities found in natural coastlines. There are difficult problems. One reason for this is not only that there is a physical gradient on the natural coastline, but also the habitat 2 of the wet plants 3 such as reed as shown in FIG. 8B (hereinafter referred to as reed field 2).・ Multiple living habitats such as the tidal flat 4 that is the habitat of the tidal flat 5 and the algae ground 6 that is the habitat of the algae 7 are spatially connected or adjacent to each other. In the preserved and reclaimed tidal flat 33 and the seaweed bed 35, there are only some components of nature alone. For example, some organisms that inhabit the natural coastline require multiple habitats depending on their lifestyle (feeding ground, spawning ground, resting area, etc.) and life history (floating larvae, infants, adults, etc.) There is something to do. In order to conserve or regenerate the coastline where various creatures including such creatures can live, multiple biological habitats such as Yoshihara 2, Tidal Flat 4, Seaweed Place 6, etc. are spatially linked or integrated. Need to play.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide a coastal wetland breeding method and a coastal wetland that can preserve or regenerate Yoshihara and tidal flats in a spatial connection.
[0005]
[Means for Solving the Problems]
The present inventor has noted that fresh water is supplied as groundwater from the hinterland in natural coastal wetlands. A brackish water area is formed by mixing fresh water and seawater in the coastal wetland, and the brackish water area is the Yoshihara 2 area. Yoshihara 2 in the brackish water area is a habitat for crabs and other bird species that feed on them, and it has been reported that it has a high ability to purify water such as organic matter, nitrogen, and phosphorus. In order to cultivate Yoshihara 2, it is necessary to form a brackish water area.
[0006]
Furthermore, based on the investigation of a natural coastal wetland having a tidal flat 4 adjacent to the Yoshihara 2, the present inventor found that the groundwater level of the Yoshihara 2 and the salinity in the groundwater (hereinafter sometimes simply referred to as salinity) are tidal flats. It has been found that it changes continuously as it approaches. Figure 7 shows the survey results of groundwater level and salinity in natural coastal wetlands. The horizontal axis of each graph in the figure is the distance from the coastline (shoreline) to the survey point (that is, between the tidal flat and the survey point) Distance). Fig. (A) shows the change in the biomass (the amount of organisms) of Yoshi, which is the representative organism of Yoshihara 2, Fig. (B) shows the changes in the ground level and groundwater level of Yoshihara 2, and (C) shows the Yoshi This represents the change in the salinity (practical salinity) of Raw 2.
[0007]
From the graph of FIG. 7A, it can be seen that the biomass of reed in the reed field 2 decreases according to the distance from the shoreline, except in the vicinity of the shoreline. As shown in the figure (B), the depth of the groundwater surface (the difference between the ground level and the groundwater level) increases according to the distance from the shoreline. It turns out that it is an increase. Moreover, since salinity is very high in the vicinity of a shoreline as shown to the same figure (C), it turns out that the decrease factor of the biomass of reed in the vicinity of a shoreline is the increase in salinity. That is, the sea-side boundary of the Yoshihara 2 is defined by salinity, and the land-side boundary is defined by the depth of the groundwater surface indicating the moisture content of the soil.
[0008]
At the boundary between the natural Yoshihara 2 and the tidal flat 4, the wetland 3 of the Yoshihara 2 gradually decreases and the tidal flat 5 that requires salt gradually increases, so the boundary line is not always clear. . It is considered that the factor that enables the spatial connection or adjoining of the two living habitats such as Yoshihara 2 and Tidal Flat 4 is the continuous change in salinity as shown in FIG. Such a continuous change in salinity is formed by a continuous change in the groundwater level as shown in FIG. If the groundwater level is formed so as to cause a continuous change in the salinity when the coastal wetland is cultivated, it can be expected that the Yoshihara 2 and the tidal flat 4 are connected spatially. The present invention has been completed as a result of research and development based on this finding.
[0009]
Referring to the embodiment of FIG. 1, the coastal wetland breeding method of the present invention is a shore separated by a distance L (see FIG. 1B) from the shoreline of the coastal soil 13 that gently descends from the shore 10 to the seabed . A fresh water passage 21 having a water level height ΔH (see Fig. B) is installed along the side with a permeable wall 22 and a filter material 28 is installed in the fresh water passage 21 to prevent inhalation of coastal soil 13 Then, the flow velocity u ( ) is formed by the permeable wall 22 so as to form a groundwater level 15 having a hydrodynamic gradient (ΔH / L) that extends from the water level height ΔH of the freshwater channel 21 to the vicinity of the shoreline according to the permeability coefficient k of the coastal soil 13. = K · ΔH / L) or by supplying fresh water 12 into the coastal soil 13 at a flow rate Q. The water level height ΔH of the fresh water channel 21 is the depth at which the groundwater level 15 is suitable for the inhabiting of the wet plants 3 and height made Sato, it is desirable that the sandy soil particle size suitable coastal soil 13 to Shisseshokubutsu 3.
[0010]
Also in reference to the embodiment of FIGS. 1 and 4, coastal wetlands present invention, a predetermined hydraulic conductivity k coastal soil 13 which soil dressing by gently inclined downward from the shore 10 to bottom, from the shoreline coastal soil 13 predetermined distance L (FIG. 1 (B) refer) separated the shore predetermined water level height above the shoreline provided via the permeable wall 22 along the side [Delta] H (FIG. (freshwater flow path 21 of the B reference), and fresh water flow A filter material 28 that prevents the suction of the coastal soil 13 installed in the road 21 is provided, and the permeable water 22 connects the water level height ΔH of the freshwater channel 21 to the vicinity of the shoreline according to the permeability coefficient k of the coastal soil 13. Fresh water 12 is supplied into the coastal soil 13 at a flow velocity u (= k · ΔH / L) or a flow rate Q at which a groundwater level 15 having a gradient (ΔH / L) is formed .
[0011]
Preferably, as shown in FIG. 1 (A), a tidal flat sediment 18 is provided on the coastal soil 13 between the high tide shoreline and the low tide shoreline. The tidal flat sediment 18 may be of a particle size suitable for the inhabiting of crab, shellfish and / or polychaete. More preferably, the bottom soil 19 of the algae ground suitable for the inhabiting of the algae 7 is provided at a site lower than the low tide shoreline on the coastal soil 13. Here, the high tide line is the intersection of the average high tide line HWL and the coastal soil 13, and the low tide line is the intersection of the average low tide line LWL and the coastal soil 13.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
1 and 4 show an embodiment of the present invention for nurturing a coastal wetland that gently descends in a direction from the shore 10 toward the offshore. An example of a marine wetland breeding target according to the present invention is coastal soil 13 artificially soiled on a submerged dike 32 as shown in FIG. However, the present invention is not limited to the application to the artificially constructed coastal soil 13; for example, as shown in FIG. 1, the present invention is applied to a natural or artificial coastal soil 13 with a weak ecosystem to It can be used for maintenance and regeneration.
[0013]
In order to cultivate the coastal wetland, a fresh water supply facility 20 for supplying fresh water 12 to the coastal soil 13 at a height higher than the shoreline is provided. The fresh water supply facility 20 in the illustrated example has a fresh water channel 21 provided along the shore 10 side of the coastal soil 13 via a permeable wall 22, and the fresh water 12 is supplied from the fresh water channel 21 through the permeable wall 22 to the coastal soil. Supply to 13. For example, fresh water 12 such as river water, ground water, rainwater, etc. is guided to the fresh water flow path 21 by a fresh water introduction means 30 such as a pump, and the fresh water flow path 21 is kept at a required water level above the shoreline. (See FIG. 4). As will be described later, the water-permeable wall 22 is sufficient if it passes the fresh water 12 at a required flow rate or flow rate. For example, a water-permeable concrete wall, a wall provided with appropriate holes, or a masonry wall can be used. Alternatively, the fresh water channel 21 may be formed of a perforated pipe, and the peripheral wall of the perforated pipe may be the water permeable wall 22.
[0014]
If the coastal soil 13 is composed of sandy soil, silt, clay, or other fine-grained soil, the freshwater flow is prevented so that the coastal soil 13 does not leak into the freshwater flow path 21 through the permeable wall 22. It is desirable to install a filter material 28 to prevent the suction of the coastal soil 13 in the road 21 (see FIG. 4). As the filter material 28, a gravel material with an adjusted particle size, a sandproof sheet, a filter unit (crushed stone bag), or the like can be used. For example, a perforated tube is laid inside the filter material 28 to form the fresh water channel 21. Further, the fresh water 12 can be supplied from the upper part of the filter material 28 to form the fresh water channel 21.
[0015]
A part of the fresh water 12 introduced into the fresh water channel 21 is supplied into the coastal soil 13 through the permeable wall 22. Seawater 11 stays below the shoreline of coastal soil 13, but freshwater 12 has a lower specific gravity than seawater 11, so the supplied freshwater 12 floats on the seawater 11 and has a groundwater level 15 above the shoreline. Form. However, the fresh water supply facility 20 in the present invention is not limited to the example shown in the figure, and it is sufficient if it can supply the fresh water 12 from a height higher than the shoreline. For example, the fresh water 12 is supplied by watering the surface of the coastal soil 13. It is good.
[0016]
In order to keep the fresh water 12 in the fresh water passage 21 at the required water level, a drain pit 25 with an overflow weir 26 is provided in the fresh water passage 21 in FIG. 4 and excess water out of the fresh water 12 introduced into the fresh water passage 21 is overflowed. It is led into the drainage pit 25 by the weir 26 and discharged to the sea area through the drainage channel 27. However, the method for maintaining the fresh water level is not limited to the illustrated example, and for example, the required fresh water level may be maintained by adjusting the amount of fresh water introduced.
[0017]
When the bottom of the fresh water passage 21 is below the shoreline, seawater 11 having a specific gravity greater than that of the fresh water 12 may flow into the fresh water passage 21, so that a permeable wall as shown in FIGS. 4B and 4C It is preferable that only a portion of 22 or more shorelines is the water permeable portion 23 and a portion of the shoreline or less is the non-permeable portion 24. Further, as shown in FIG. 1, it is possible to prevent the inflow of the seawater 11 into the freshwater flow channel 21 by making the bottom of the freshwater flow channel 21 higher than the high tide shoreline.
[0018]
In order to inhabit the marine plants 3 such as reeds, nagamino-onishiba, kusayoshi, iashi, sei-gishi, fukudo, uragiku, shiakugu (Cyperaceae), hornbill, etc. Either sandy soil or sandy soil having a grain size suitable for the wet marine plant 3 is provided in a region above the shoreline on the coastal soil 13. For example, soil with a particle size of about 0.2 mm is preferred for reeds, and it has been reported that it is inappropriate for gravel and rocks that are too large, silt and clay that are too small. For this reason, when reeds inhabit on the coastal soil 13, sandy soil having a particle size of about 0.02 to 0.3 mm is provided in the region above the shoreline on the coastal soil 13. In addition, there is a report that a soil thickness of 50-60 cm is necessary for the growth of reeds. For example, the median particle size (particle size with a passing mass percentage of 50%) on the coastal soil 13 is about 0.02-0.3 mm. It is desirable to make sandy soil with a thickness of 50-60cm.
[0019]
In addition, it is desirable that the groundwater level 15 in the coastal soil 13 has a depth suitable for the inhabiting of the wet plants 3. The present inventor has found that the biomass of reed decreases when the depth of groundwater surface (difference between ground level and groundwater level) d is 15 cm or more, and significantly decreases when the depth is 35 cm or more. I found. For this reason, when reeds are inhabited, the depth d of the groundwater surface in the coastal soil 13 is 35 cm or less, preferably 15 cm or less. In order to form such a groundwater level 15, for example, as shown in FIG. 1 (B), a fresh water channel 21 is provided at a position higher by H ₁ than the tide, and the fresh water level in the fresh water channel 21, that is, fresh water Keep 11 heads higher than the tide by ΔH (= H ₁ -d).
[0020]
Furthermore, in order to inhabit the marine plants 3 in the coastal soil 13, a gradient higher than the shoreline of the coastal soil 13 can be determined so that the appropriate groundwater level 15 can be secured in a wide range. In FIG. 1, the freshwater channel 21 is provided at a distance L from the shoreline, and the groundwater level 15 is gradually lowered from the freshwater channel 21 to the vicinity of the shoreline according to the gentle slope of the coastal soil 13. In this case, the dynamic gradient i of the groundwater 14 at the time of high tide is ΔH / L as shown in FIG. On the other hand, the hydraulic conductivity k of the coastal soil 13 can be determined from the grain size of the coastal soil 13 described above. The movement of groundwater 14 in the soil is known to follow Darcy's law expressed by the following formula (1) or (2), and forms a groundwater level 15 with a hydrodynamic gradient i in the coastal soil 13 with a permeability coefficient k. In order to do this, the permeable wall 22 may be designed so that the fresh water 12 is supplied to the coastal soil 13 at the flow velocity u of the formula (1) or the flow rate Q of the formula (2). The water flow rate Q is represented by the product of the water flow velocity u and the cross-sectional area A of the water permeable holes 22.
[0021]
[Expression 1]
u = ki = k · (ΔH / L) …………………………………………… (1)
Q = Au = A · ki = A · k · (ΔH / L) ……………………………… (2)
[0022]
If the fresh water 12 is supplied into the coastal soil 13 having the permeability coefficient k at the flow velocity u or the flow rate Q as described above, a groundwater level 15 connected from the fresh water supply site to the vicinity of the shoreline can be formed as shown in FIG. That is, as described with reference to FIG. 7, a groundwater level 15 similar to that of a natural coastal wetland in which the depth of the groundwater surface gradually decreases as it approaches the tidal flat can be formed in the coastal soil 13. Further, if the groundwater level 15 in which the depth of the groundwater surface continuously changes is formed in this way, a continuous change in salinity from fresh water to seawater can be created in the coastal soil 13. For example, there is a report that reeds have a germination rate that drops when salinity is 10 PSU or higher, and the limit of habitability is 20 PSU or higher. For this reason, by forming the groundwater level 15 so as to ensure a wide range in which the salinity is 20 PSU or less, preferably 10 PSU or less, reeds can be inhabited to the vicinity of the shoreline.
[0023]
Preferably, tidal flat organisms such as clams, crabs, coral species, etc. should be inhabited by placing the tidal flat bottom soil 18 on the coastal soil 13 between the high tide shoreline and the low tide shoreline. Can do. According to the inventor's investigation, for example, the salt content that can be infested by crabs is 0.2 PSU or more, and 5 PSU or more is desirable for the inhabiting juvenile crabs. In the present invention, the fresh water 12 supplied to the coastal soil 13 is not directly allowed to flow into the tidal flat bottom soil 18, but is flowed in after increasing the salinity according to the approach to the shoreline. Can be used as a habitat for tidal flats such as crab. At low tide, a groundwater level 15 is formed near the surface of the tidal flat sediment 18 as shown in FIG. 1C. In this case, the salinity of the groundwater 14 is about the same as that of seawater. The influence of the inflow of groundwater 14 on the habitat of can be minimized.
[0024]
The present invention forms a groundwater level 15 in the coastal soil 13 where the salinity gradually increases with the approach to the shoreline, so that the boundary between the brackish plants 3 in the brackish water area and the tidal flat organisms 5 in the sea area coexists. The area can be created, and the two living habitats of Yoshihara 2 and Tidal Flat 4 can be brought together spatially. In addition, since the groundwater level 15 is maintained near the ground surface even at low tide, the portion between the high tide shoreline and the low tide shoreline can be kept in a wet state suitable for the inhabiting of the tidal flat organisms 5. In addition, according to the present invention, the Yoshihara 2 and the tidal flat 4 can be connected or adjacent to each other, but if necessary, a buffer zone, a step or the like may be provided between them.
[0025]
In this way, it is possible to provide “a marine wetland breeding method and a marine wetland capable of preserving or regenerating Yoshihara and tidal flats in a spatial connection”, which is an object of the present invention.
[0026]
Preferably, as shown in FIG. 1 (A), an algal bed bottom sediment 19 suitable for inhabiting algae 7 is provided at a suitable depth at a site lower than the low tide shoreline on the coastal soil 13. It is possible to cultivate the three biological habitats of Yoshihara 2, Tidal Flats 4, and Algae 6 on the coastal soil 13 by uniting the bottom soil 19 of the seaweed ground. The development of a healthy coastline very close to nature can be expected.
[0027]
In addition, although Yoshihara 2 and tidal flats 4 cannot be grown in extremely organically contaminated soil, some organic matter is required for growing Yoshihara 2 and tidal flats 4. For example, in the case of reeds, it is said that as organic matter in the soil decreases, reeds will decline and transition to water moss. For this reason, for example, fresh water 12 (for example, middle water, discharged water after drainage treatment, etc.) having an appropriate organic substance concentration is supplied to the coastal soil 13, and the coastal soil 13 and the bottom sediments 18 and 19 are supplied to the wet plants 3 and tidal flat organisms. It is preferable to adjust to an ignition loss suitable for 5 habitats. More preferably, the nutrient substances of the wet plants 3, the tidal flat organisms 5 and / or the algae 7 are dissolved in the fresh water 12, and these nutrient substances are supplied to the coastal soil 13 and the sediments 18 and 19. In addition, a trace element is also mentioned as a nutrient substance.
[0028]
【Example】
FIG. 2 shows another embodiment of the present invention in which a groundwater level 15 higher than that in FIG. 1 (B) is formed. The present invention forms a salinity concentration gradient as shown in FIG. 7 (C), which changes according to the distance from the shoreline in the coastal soil 13 due to the groundwater level 15. The salinity gradient depends on the amount of fresh water 12 supplied, etc. It can change accordingly. In order to ensure a wide habitat range of the wet plants 3 on the coastal soil 13, it is desirable that the salinity is low enough that the wet plants 3 can live up to the vicinity of the shoreline. However, for example, when the amount of fresh water is small, the salinity in the vicinity of the shoreline may be higher than the inhabitable range of the wet plants 3.
[0029]
In FIG. 2, by adjusting the groundwater level 15, the salinity gradient from the fresh water to the salt water in the coastal soil 13 is set to a range suitable for the inhabiting of the wet plants 3. That is, by forming a groundwater level 15 that continues from the freshwater supply site to a site that is higher than the shoreline by δ, the salinity in the vicinity of the shoreline is kept lower than in the case of FIG. The salinity in the vicinity of the shoreline can be within a range in which the wet plants 3 can live.
[0030]
FIG. 3 shows an embodiment of the present invention in which impermeable layers 17a, 17b, and 17c for setting the groundwater level 15 to the required depth in the coastal soil 13 are provided. As described above, the permeability coefficient k of the coastal soil 13 is determined from the particle size and the like. However, depending on the particle size of the coastal soil 13, it may be difficult to set the groundwater level 15 at a depth suitable for the inhabiting of the wet plants 3. In such a case, it is possible to adjust the groundwater level 15 by providing an appropriate impermeable layer 17 in the coastal soil 13. In the illustrated example, the three impermeable layers 17a, 17b, and 17c are provided in the vertical direction in the coastal soil 13, but the number and arrangement of the impermeable layers 17 are not limited to the illustrated example. For example, it is possible to adjust the groundwater level 15 in the coastal soil 13 by providing an impermeable layer 17 having a horizontal or required gradient.
[0031]
The present invention can be effectively used for the maintenance and regeneration of a coastline straightened by an upright revetment 8 as shown in FIG. In the embodiment of FIG. 5, the coastal soil 13 is gently lowered and inclined in the direction from the shore 10 toward the offshore, and the area between the high tide shoreline and the low tide shoreline on the coastal soil 13 and at the time of low tide. Inhabiting environment of wet plants 3, tidal flat organisms 5, and algae 7 along the direction from the shore 10 to the offshore by depositing the tidal flat bottom soil 18 and the seaweed bottom sediment 19 respectively below the shoreline Are fostered by connecting them spatially. By nurturing Yoshihara 2, Tidal Flats 4, and Algae 6 in an integrated manner, it is possible to revive ecosystems that are rich in both types and quantities close to nature. Further, in the figure, a freshwater introduction hole 34 is drilled in the revetment 8 (that is, the revetment 8 has a permeable wall structure), and the freshwater flow path 21 on the shore side of the revetment 8 passes through the introduction hole 34 to the coastal soil 13 on the sea side. Fresh water 12 is supplied. However, the supply method of the fresh water 12 is not limited to the illustrated example.
[0032]
However, when the Yoshihara 2, the tidal flat 4 and the seaweed basin 6 are integrally grown as shown in FIG. 5, the distance in the offshore direction may be a problem. Since the tidal flat sediment 18 includes mud and silt, it is necessary to make the tidal flat 4 have a gentle slope in order to avoid the outflow of the tidal bottom sediment 18. In addition, Yoshihara 2 also needs a gentle slope in order to secure a proper groundwater level 15 in a wide range. Furthermore, in order to grow the seaweed bed 6 on the offshore seabed, a longer distance in the offshore direction is required. When the water area of the seaside front of the revetment 8 is narrow, it may be difficult to cultivate a coastal wetland by the method of FIG. Moreover, since the scale of the entire coastal wetland becomes very large, the feasibility as an artificial structure may be difficult.
[0033]
In the embodiment of FIG. 6, in order to create a coastal wetland with a gentle slope, instead of the direction from the shore 10 toward the offshore, the Yoshihara 2, the tidal flat 4 and the seaweed basin 6 are connected together along the shore 10 to be integrated. Examples of training are shown below. In the same figure (A) and (B), a discontinuous wave-dissipating wall 36 is provided on the sea side along the revetment 8, and the coastal soil 13 is placed between the revetment 8 and the wave-dissipating wall 36 in parallel with the revetment 8 and The discontinuous part 37 of the wave-dissipating wall 36 is gently lowered and inclined so that it becomes lower than the tideline at low tide, and the seawater 11 enters the coastal soil 13 from the discontinuous part 37 of the wave-dissipating wall 36 and is wet. Living plants 3, tidal flats 5 and algae 7 are grown along the bank 8. In this way, regenerating Yoshihara 2, Tidal Flat 4, and Algae 6 along the shore 10 will make a relatively small coastal wetland with a suitable slope in front of the revetment 8, even if the water area in front of the existing revetment is narrow. Can be constructed as a scale man-made structure.
[0034]
In addition, as shown in FIG. 6 (C), the coastal soil 13 is parallel to the revetment 8 on the back side (shore 10 side) where a part of the revetment 8 is excavated, not the front surface of the revetment 8, and the excavation part 39 is a low tide coastline. Gently descend the slope so that it becomes lower, and the soil is infiltrated into the coastal soil 13 from the excavation section 39, so that the Yoshihara 2, the tidal flat 4, and the seaweed bed 6 are integrated along the revetment 8. It can also be nurtured.
[0035]
【The invention's effect】
As described above, the coastal wetland breeding method and the coastal wetland according to the present invention supply fresh water from a height higher than the shoreline to the coastal soil gently descending from the shore to the seabed, and continue from the freshwater supply site to the vicinity of the shoreline. Since the groundwater level is formed, the following remarkable effects are produced.
[0036]
(B) The required salinity gradient from fresh water to salt water can be formed in the coastal soil, and the Yoshihara and tidal flats can be linked together and grown together.
(B) Since the groundwater formed in the coastal soil is increased in salinity and flows into the vicinity of the shoreline, it is possible to keep the tidal flat moist while minimizing the impact on the tidal flat organisms.
(C) Since multiple biological habitats such as Yoshihara and Tidal Flats can be brought together spatially, it can be expected to create a natural ecosystem rich in variety and quantity.
(D) A coastal wetland that is closer to the natural tidal flat can be nurtured by subsidizing the tidal flat bottom soil between the high tide shoreline and the low tide shoreline.
(E) Furthermore, by cultivating a coastline that is extremely close to nature by reclaiming the Yoshihara, Tidal Flats, and algae basin in a unified manner by placing the soil in the bottom of the algae basin below the low tide shoreline. I can expect.
(F) It can be expected to contribute to a coastal rehabilitation project that regenerates the existing coastline straightened by upright revetments into a natural coastline with a slope.
(G) By growing reed fields, tidal flats, and seaweed beds along the shore, it is possible to cultivate coastal wetlands with gentle slopes even in narrow waters.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of the present invention.
FIG. 2 is an explanatory diagram of another embodiment of the present invention.
FIG. 3 is an explanatory view of still another embodiment of the present invention in which an impermeable layer is provided.
FIG. 4 is an explanatory view of an embodiment of the fresh water supply equipment used in the present invention, (A) is a plan view, and (B), (C) and (D) are B in the plan view (A), respectively. It is sectional drawing in -B, CC, and DD.
FIG. 5 is an explanatory view of an embodiment of the present invention in which Yoshihara, Tidal Flats, and Seaweed beds are grown in a direction from the shore to the offing.
FIG. 6 is an explanatory diagram of another embodiment of the present invention in which Yoshihara, Tidal Flats, and algae beds are grown along the shore, and (B) and (C) are examples of plan views, A) is a cross-sectional view taken along the line AA of the plan view (B) or (C).
FIG. 7 is a graph showing changes in biomass, groundwater level, and salinity concentration in Yoshihara.
FIG. 8 is an explanatory diagram showing a difference between a coastline (A) provided with a conventional upright revetment and a natural coastline (B).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Rinkai marsh 2 ... Yoshihara 3 ... Moisture plant 4 ... Tidal flat 5 ... Tidal flat organism 6 ... Algae 7 ... Algae 8 ... Upright revetment 9 ... Landfill 10 ... Shore
11 ... Seawater 12 ... Fresh water
13 ... Coastal soil 14 ... Groundwater
15 ... Groundwater level
17 ... Impervious layer 18 ... Tidal flat sediment
19 ... bottom soil of seaweed bed 20 ... fresh water supply equipment
21 ... Fresh water channel 22 ... Permeable wall
23 ... Water-permeable part 24 ... Water-impermeable part
25 ... Drainage pit 26 ... Overflow weir
27… Drainage channel 28… Filter material
30 ... Freshwater introduction means 32 ... Submarine
33 ... Tidal flat 34 ... Fresh water introduction hole
35 ... Algae 36 ... Disappearing wall
37 ... Discontinuous part 39 ... Cut-off part

Claims

A freshwater channel with a water level higher than the shoreline is provided along the shoreline that is separated from the shoreline of the coastal soil that gently descends from the shore to the seabed via a permeable wall, and sucks coastal soil into the freshwater channel. A filter material is installed to prevent the fresh water from flowing into the coastal soil at a flow velocity or flow rate at which a hydrodynamic gradient groundwater level is formed from the water level height of the freshwater flow path to the shoreline according to the permeability coefficient of the coastal soil. A method for nurturing coastal wetlands that are supplied inside .

In growing method according to claim 1, coastal wetland method of growing a water level height of the fresh water flow path the groundwater level formed by the height a depth suitable for the habitat of Shisseshokubutsu.

The cultivation method of Claim 1 or 2 WHEREIN: The cultivation method of the coastal wetland which uses the said coastal soil as sandy soil of the particle size suitable for a marine plant.

4. The method for cultivating a marine wetland according to claim 1, wherein an impermeable layer is provided in the coastal soil to make a groundwater level a required depth.

The method for growing a marine wetland according to any one of claims 1 to 4, wherein a salinity gradient from fresh water to salt water in the ground water is adapted to inhabit the marine plants by adjusting the ground water level.

6. The method for cultivating a marine wetland according to any one of claims 1 to 5, wherein a tidal flat bottom soil is provided at a site between the high tide shoreline and a low tide shoreline on the coastal soil.

7. The method for cultivating a marine wetland according to claim 6, wherein the tidal flat sediment is of a particle size suitable for the inhabiting of crab, shellfish and / or polychaete.

The breeding method according to any one of claims 1 to 7, wherein a marine wetland soil suitable for algae inhabiting is placed at a site lower than the low tide shoreline on the coastal soil.

The growing method according to claim 1, wherein a marine wetland, a tidal flat, and / or algae nutrients are dissolved in the fresh water.

10. The method for cultivating a marine wetland according to any one of claims 1 to 9, wherein the fresh water is used as river water, ground water, rain water, middle water or discharged water after drainage treatment with an appropriate organic substance concentration.

The breeding method according to any one of claims 8 to 10, wherein the coastal soil is gently inclined downward in a direction from the shore to the offshore, and the marine plants, tidal flats, A method for nurturing coastal wetlands by cultivating the algae habitat.

The growing method according to any one of claims 8 to 10, wherein a discontinuous wave-dissipating wall is provided in parallel with the shore, and the coastal soil is gently inclined downward along the shore between the shore and the wave-dissipating wall, and The habitat of wet plants, tidal flats, and algae that continue along the shore by intruding the seawater into the coastal soil from the discontinuity by disposing the discontinuity of the wave-dissipating wall below the tideline at low tide A method for nurturing coastal wetlands by nurturing the environment.

Coastal soil predetermined permeability that soil dressing by gently slopes downward to the sea floor from the shore, the predetermined water level height above the shoreline provided via the permeable wall from the shoreline along a predetermined distance between each shore side of the coastal soil comprising a filter material to prevent fresh water flow path, and a suction coastal soil which is installed in the fresh water channel, leading to shoreline vicinity from the water level height of fresh water flow path according to the permeability of the coastal soil by the water permeable wall Dosui gradient formed by supplying fresh water to coastal soil at a flow rate or flow groundwater level is formed of coastal wetlands.

In wetland of claim 13, coastal wetlands water level height of the fresh water flow path the groundwater level formed by the height a depth suitable for the habitat of Shisseshokubutsu.

The wetland according to claim 13 or 14 , wherein the coastal soil is a sandy soil having a particle size suitable for marine plants.

The wetland according to any one of claims 13 to 15 , wherein an impermeable layer is provided in the coastal soil to make a groundwater level a required depth.

The wetland according to any one of claims 13 to 16 , wherein the coastal soil includes a tidal flat bottom soil at a site between a high tide shoreline and a low tide shoreline.

The wetland according to claim 17 , wherein the tidal flat sediment is of a particle size suitable for the inhabiting of crab, shellfish and / or polychaete.

19. The marine wetland according to any one of claims 13 to 18 , wherein the bottom soil on the coastal soil is lower than the low tide shoreline and the bottom soil of algae ground suitable for algae habitat is visited.

The wetland according to any one of claims 13 to 19 , wherein a marine wetland, a tidal flat and / or algae nutrients are dissolved in the fresh water.

21. The coastal wetland according to claim 20 , wherein the fresh water is used as river water, groundwater, rainwater, middle water or discharged water after drainage treatment with an appropriate organic substance concentration.

The marine wetland according to any one of claims 19 to 21 , wherein the coastal soil is gently landed and inclined in a direction from the shore toward the offshore.

A wetland according to any one of claims 19 to 21 , wherein a discontinuous wave-dissipating wall is provided in parallel with the shore, and the coastal soil is gently lowered and inclined along the shore between the shore and the wave-dissipating wall, and A coastal wetland where the discontinuous part of the wave-dissipating wall is a land that is lower than the low tide shoreline.