Song va lu

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Bo co a Cht Mi Trng Nhm 9

SONG VA LUA . SONG:1) Khai quat ve song:* Khai niem:- Song suoi la nhng dong nc chay theo ranh hay longmang ro rang. Song th co long mang to rong va co chieudai that quan trong so vi suoi. (a chat c s)- Song la dong nc lu lng ln thng xuyen chay, conguon cung chu yeu la t cac ho nc, t cac con suoihay khe nui hay t cac con song nho hn ni co o caohn, cac nguon nc co c do nc ma (Wikipedia tiengViet).* Nguon goc hnh thanh:- Khi ma ri xuong mat at hay tuyet tan, mot phan cthc vat hap thu roi boc hi vao khong kh, mot phan bochi trc tiep t mat at , phan khac tham sau xuong atthanh nc ngam. Phan con lai chay tran tren mat at segom vao cac long mang t nhien goi chung la nc chaydong tao ra song suoi.

2) He thong song:

2.1/ Lu vc:

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- Lu vc la toan the mot vung ma ni o suoi va phu lu a tiep nhan c mot lng nc e cung cap chosong chnh. Tuy nhien, moi phu lu va suoi eu co motphu lu rieng re. Moi dong chay la mot nhanh nhonhat cua mot phu lu. Cac phu lu noi lai tao thanh

mot lu vc rong ln.- Co 5 kieu lu vc chnh:He thong song co dang hnh nhanh cay (thu trang)(dendritic pattern): thng gap nhng vung ata co khang sc ong eu.He thong song co dang hnh mang li (trellispattern): nhng vung at a xep thanh lp vab uon nep nh cat ket (sa thach) va diep thach,dong nc chay theo hng lp hay thang gocvi hng lp, tao nen mot he thong song vidang hnh mang li that ac biet.He thong song co dang hnh tia (radial pattern): cac nh nui cao he thong song phu co dang hnhtia ly tam hay hng tam.ay la kieu mang songphat trien tren sn mot nui la mi hnh thanh.He thong song co dang hnh goc (rectangularpattern): kieu lu vc nay phat trien nen a cohe thong ng nt thang goc nhau.He thong song co dang song song: trong khu vcnen a tao mot trien doc, cac song nhanh codang song song vi nhau.

2.2/ Trac dien song:- Trac dien cua mot con song gom co 3 phan: thnglu, trung lu va ha lu song.

Thng lu song: ay la ni song bat nguon, ngvi thi ky song tre. Nc chay xiet, hoat ong

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xam thc dien ra rat manh liet, ay song ngaycang c ao sau, tao ra hai b vach thangng, hp thanh hnh ch V. thng lu song corat nhieu ghenh thac.

Trung lu song: ay la oan gia cua song, ng

vi giai oan song trng thanh. giai oan nay,o doc cua long song giam i nhieu, nc chaycham lai, co t hay khong co ghenh thac. Songkhong khi sau long na ma ao hai ben b mrong thung lung song. Long song tr nen uonkhuc, doc ben b ong boi bat au hnh thanh.Ha lu song: la phan cuoi cua con song hay motoan song gia. ay nc cham lai, song khongcon sc tan pha na, ma ch lang tu cac loaivat lieu a van chuyen. Thung lung song trthanh ong bang rong ln. Long song uon khucngoan ngoeo va khi ra en bien, song lai cphan chia thanh nhieu nhanh thao nc. Ncsong trai rong, gan nh khong phan biet cvach song. ong boi thanh lap chu yeu trong khuvc nay.

- Trac dien doc theo long song c bieu dien bangmot ng cong, vi o doc thay oi t thng lu enha lu song. Ban au, ng vi khu vc thng lu, odoc ha nhanh chong va sau o giam dan cho en mcthap nhat, goi la mc goc. Mc goc cua mot con songtng ng vi mc bien hay mc nc ho ma con songo o vao.

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3) S lu chuyen cua dong nc tren song:3.1/ Cac nhan to tng tac anh hng en s

can bang cua dong chay:- Lu lng (Discharge).- Lu toc (Velocity).- Tai lng (Load).- Gradient.

- Cau truc dong chay hay o khuc khuyu cua dongchay (channel pattern).

3.2/ Chuyen ong cua dong chay:- Chay tang (laminar flow): cac oan song thang, aysong trn lang, lu toc cham, nc lu chuyen thanhlp song song. Moi mot lp di chuyen vi van tockhong oi, lp nay khac vi lp ke can. Cac lp setach ra quanh chng ngai vat va ket hp lai phacuoi dong.- Chay roi (turbulent flow): la phng thc chay chnh cua

dong chay. Chay roi xuat hien khi gia toc gia tanghoac ay song go ghe, ng i cua phan t nc bpha v khi gap phai dong xoay. Khi lu toc chay qualn hoac long song co nhieu chng ngai vat, ncse chuyen t cach chay roi yen lang thanh chay roicuon vong.

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3.3/ Lu lng, gradient, lu toc:* Lu toc:- Lu toc tai mot v tr cua dong song la oan ngma nc chay qua trong mot thi gian nh trc (n vm/s).- Theo ly thuyet, lu toc tang dan eu nhng tren thcte, lu toc phu thuoc vao cac yeu to:

o loi lom (C) cua ay song.Ban knh (R) cua thiet dien long song.o doc (I).

- Cong thc tnh lu toc cua mot dong song: RI C V =

- Lu toc khoang t 15 cm/s la tng oi cham, Lu toctng oi cao khi nc chay t 625 en 750 cm/s, lu toccao khi len en 10 m/s (1000 cm/s).

* Gradient:- Gradient cua dong chay la khoang cach thang ngcua dong chay o xuong trong mot khoang cach conh so vi dong chay nam ngang.VD:

Thng lu song Yaba (california My) khoang 20km,gradient trung bnh 42 m/km.

Thng lu song Uncompahne (Colorado My) 6,5 km,gradient trung bnh 66 m/km.

- S giam gradient ni ha nguon cua dong song mot

phan do gii han cua mc o xam thc (limitations of base level).

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- Lu lng thay oi khong ch nhng dong chaykhac nhau ma con thay oi ngay trong mot dong chayt thi iem nay sang thi iem khac, t ni nay enni khac trong tien trnh chay cua no.- Lu lng co xu hng gia tang cuoi dong do co

nhieu phu lu cap them nc vao dong chnh. Lu muaxuan co the lam dong chay tang cao, hnh thanh dongchay xiet d doi.

3.4/ Bieu o thuy lng:- Bieu o thuy lng cua mot dong song cho thay s thay oi cua lu lng qua thi gian.- Dang bieu o thuy lng cua nhng dong chay khacnhau (ngay ca nhng iem khac nhau tren cung motdong) thay oi theo cac yeu to t nhien nh toc otham loc, a hnh, a chat va lp phu thc vat.

4) Hoat ong cua dong chay hay cac qua trnh song(river processes):

4.1/ Tac dung van chuyen:- Trong khi di chuyen, dong song se mang i cac vat lieu ay song, vat lieu do ra troi hai b, cua phu luhay cua cac khoi. Cac vat lieu nay c lang ong ch cuoi la ai dng. Lng vat lieu c dong songmang i c goi la tai trong (load). Kch thc hat toi ama song co the mang i la tieu chuan dung e anhgia nang lng van chuyen (competence).

- Co 3 phng thc van chuyen vat lieu: Hoa tan trong nc. L lng trong nc. Di chuyen sat ay song.

* Hoa tan trong nc:+ Trong thien nhien hoan toan khong co nc tinhkhiet. Ma ri va tham xuong at, nc hoa tancac hp chat co trong at. Trong khi di chuyen,nc se ngam qua cac khe nt, lo hong, machquang trong a goc va hoa tan them cac vatchat tren ng i cua no. Cuoi cung, phan lnnc nay xuat lo cac mc thap hn.+ Lng vat chat hoa tan trong nc tuy thuocvao thi gian, mua va v tr a chat. Vat chathoa tan c o bang on v mot phan trieu (ppm).

* L lng trong nc:

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+ Cac hat ran c dong xoay cuon i theo dongchay trang thai l lng. Qua trnh van chuyennay b khong che bi hai yeu to: s cuon xoaycua nc va van toc ti han.+ Chuyen ong xoay cua dong roi di chuyen theo

cac quy ao, hat ri vao dong xoay se noi lenva trang thai l lng cho en khi van toc cuanc xoay can bang hay ln hn van toc ti hancua hat.+ Van toc ti han gia tang theo kch thc cuacac hat co cung hnh dang va t trong.+ Do phng thc l lng nay, bun va set cphan bo eu tren ay, con nhng hat ln hnnh cat c dong xoay manh van chuyen vecuoi dong vi so lng ln trong i xao ongnhat.

* Di chuyen sat ay:+ Ngc vi tai trong hoa tan va l lng, loai vatlieu doc theo ay song c goi la tram tch ay(bed load). Ca loai vat lieu nay thng la cac loaicat tho, san soi nang.+ Cac phan t ay nay thng di chuyen theo 3phng thc sau:

o Nhay coc (saltation).o Lan tron (rolling).o Trt (slide).

4.2/ S xam thc:- Xam thc c hoc hay hien tng bao mon la do cacloai vat lieu cng c dong nc van chuyen va chamcha xat lam mon nhan long song hay a tang aysong.

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- S bao mon con tao ra ay song nhng ho sau(noi khong lo). Cac ho nay hnh thanh la do at acau tao ay song khong co khang sc ong eu,ni nao mem th b dong nc khoet trung xuongnhanh, san soi do dong nc van chuyen ri vao trong

o, khi nc chay nhanh at en lu toc 10 m/s tr len,san soi nay se b xoay tron ay trung, bao mon bvach, lan hoi tao thanh cac ho sau co dang tng t nh nhng chiec noi to.- Noi khong lo co the do cac xoay nc tren matao khoet ay song tao thanh.- Ngoai cac trung sau ay song con co cac trungsau tao thanh do nc t tren trien cao o xuong,xoay manh vao nen a tao thanh. Loai trung naythng thay chan cac ghenh thac.

4.3/ S tram tch:- Khi van toc dong chay giam, thap hn mc can thiete gi vat l lng, dong chay bat au lang ong taitrong l lng cua no. S tram tch la mot qua trnhchon loc. Trc het, cac hat tho ri xuong, sau o vvan toc giam (nang lng cung giam) cac hat mn hncung lang ong.

5) Cac canh quan do song tao ra:5.1/ Cac canh quan hnh thanh khu vc thng lu

song:

* Thac:- ay la mot trong cac canh quan thu v. Tuy hoat onghet sc manh me nh thc ra trong lch s cua dongsong, chung co mot i song het sc ngan ngui.

Thac c hnh thanh do s ha thap o cao ot ngottren tiet dien doc cua dong song. S ha thap o caonay co the bien mat theo thi gian.

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* Ghenh (rapid): - Giong nh thac, ghenh c hnh thanh khi co s giatang ot ngot ve o doc cua long song, nhng ghenh th nc khong o manh xuong nh thac. oi khighenh c phat trien trc tiep t cac thac co trco.

5.2/ Cac canh quan hnh thanh khu vc trung luva ha lu song:

* Khuc uon song (meander):- Viec hnh thanh khuc uon bao gom ca hai qua trnhxam thc va tch tu. Trc het, vai vat can a hngdong chay vong mot ben b va dong chay se omanh vao b oi dien, ni co dong chay roi manhnhat. Cac vat lieu do song xam thc b c mang vepha ha lu, sau o lang ong trong i chay roi giam gia dong song va vao pha trong cua khuc uon keo. Khi dong song chay lng t b nay sang b kia,cac khuc uon tiep tuc phat trien bang cach xam thc pha ngoai khuc uon va tram tch pha trong khucuon.- khuc uon, song xam thc ngang va xam thc saulam b di chuyen ngang va xuoi ve pha ha lu. Trongmot dong chay uon khuc nhng ni gap khuc manh,dong song se hnh thanh cac oan song bo (cutoff),dau vet khuc uon (meander scar) va ho sng trau.

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* Dong chay phan nhanh:- Tren cac bai boi, ac biet ni co so lng ln vatlieu vun c lang ong nhanh chong, dong song sehnh thanh mot he thong dong chay hoi tu va phanky phc tap gia long song. He thong nay b phancach bang cac con cat hay cac cu lao. ay la kieudong song b phan nhanh. Mo hnh nay phat trien khilu lng thay oi manh va cac b de b xam thc ecung cap tai trong ln cho dong chay. ay la ac trngcua cac vung quat boi tch, tram tch ra troi bang ha

va cua mot so dong chay rat giau phu sa.- Noi chung, o doc cua dong chay phan nhanh cao hno doc cua dong chay uon khuc co cung lu lngay dng nh la bieu th s co gang cua dong songe van chuyen c nhieu phu sa hn.

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* e thien nhien (Natural levees):- nhieu bai boi, nc song nam cao hn ay thunglung va c gi bi mot b vach bang cat va cacvat lieu dang bot goi la e thien nhien. B e docnhe t nh ve pha vach thung lung. Bai boi thap hnket hp vi e thien nhien hnh thanh am lay cu(back swamp). e c hnh thanh trong mua lu lut khinc tran b vao bai boi. Dong bun nay khong tontai lau khi van toc va s xao tron cua no giam ot

ngot, phu sa l lng c lang ong gan dong songnhng mot so ln cung c mang i xa hn va langong bai boi. Cac tram tch nay co dang mot cainem hng mui nhon ra khoi song, lau dan thanh ethien nhien co chieu cao giam dan t b song rangoai.

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- khu vc tam giac chau song Mississippi, e thiennhien cao hn am lay cu khoang t 5 6 m.- Cac e thien nhien cung co mot y ngha nhat nhtrong viec ngan hien tng lu.

* Bai boi:- Hau het cac dong song eu co bai boi vien benngoai. Cac bai boi co the rat hep (rong chng vai m)cho en rat rong (hang tram km) nh bai boi songMississippi. Bai boi co dang rat phang, ac biet khi sovi o doc cua hai vach thung lung. Nhng trong bai

boi co nhieu a hnh chenh nhau chng vai m nh cace thien nhien, dau vet khuc uon va ho sng trau.- Bai boi c hnh thanh do vat lieu cua song mangen. Co 2 loai tram tch hnh thanh bai boi: mot latram tch bot, set va cat do lu lut tran b mang vaolang ong bai boi. Loai nay goi la tram tch tranb. Loai th hai la tram tch tho gom cuoi va cat colien quan trc tiep en long song. Cac tram tch nayla vat lieu lang ong pha trong cua khuc cong haykhuc uon cua song trong giai oan nc kiet tao thanhcac doi song cau tao bang cat va cuoi, soi.

- Chung ta co the xem bai boi la mot yeu to tram tchkhong on nh. Trong mua lu, dong song tao bai boi nhieu ni va cung ong thi pha huy nhng baiboi nhng ni khac. Nh vay, bai boi tr thanh choton tr tam thi cua vat lieu tram tch.

* Tam giac chau (Delta):

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- Khi dong chay vao mot vung nc ln yen lang, vantoc va nang lng van chuyen b giam nhanh chong.Neu co u lng phu sa va neu ieu kien cua vungnc tnh thch hp th delta dan c hnh thanh. Dongnc chay qua tam giac chau b phan thanh mot loat

cac nhanh song toa ra t nh tao thanh tam giacchau.- Vat lieu tram tch cua cac song nhanh lang ong docdong chay ay va vach cua chung c dng lentrong vung chung quanh o la luc song nhanh thoatkhoi long song cu hnh thanh long song mi. Qua trnhnay c tei61p dien lam cho tam giac chau phat trienkhong ngng.- mc cuoi, cac vat lieu tram tch cua cac songnhanh co the sap xep theo mot mo hnh nhat nh:

Vat lieu tho lang ong trc hnh thanh mot loat

cac lp xien cheo goi la tang trc (foreset bed).Vat lieu mn hn c mang i xa hn va lang ong ay bien, ho goi la tang ay (bottomset bed).Khi tam giac chau phat trien xa dan, dong chayphai phat trien ng i cua no ra ngoai ra tamgiac chau, t o hnh thanh lp phu goi la tangtren (topset bed).

- Tuy nhien, rat t tam giac chau co dang ly tng nhtren do nhieu yeu to anh hng: cac dong hai lu venb, s bien ong, o nen chat cua tram tch va s lun xuong cua vo trai at.- Tam giac chau la yeu to ac trng cua nhieu songln tren the gii nh song nile, song Mississippi, songMekong.

* Quat boi tch (Alluvial fan):- Tng t nh tam giac chau. Cac quat nay ac trng chovung kho han va ban kho han nhng chung cung cothe hnh thanh bat c kh hau nao neu ieu kiencho phep.- Quat boi tch anh dau s giam nang lng ot ngotcua nang lng van chuyen cua dong chay khi nochuyen t ni doc xuong vung bang phang hn, changhan nh khi dong song chay t sn nui doc vao ongbang.- Khi van toc c khong che, dong chay yeu dan vabat au lang ong vat lieu tram tch. Cuoi cung quatc hnh thanh co o doc gan vi o doc cua dongchay khi no chay t nui xuong.

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- Trong thi gian lu lut, dong chay o tran vao ni thaphn, di ng i va se bat au s lang ong. S riepdien cua qua trnh nay lam cho quat boi tch ln dan.

* Cac them song:- Them song la mot be mat tng oi bang phangchay doc theo thung lung song, vi b doc ngan cachno vi bai boi hay them thap hn. Them song la di tchcua bai boi cao trc ay cua dong chay.- Them xam thc va tch tu (cut & fill) c hnh thanh khidong chay ban au b tram tch lap ay lam cho songphai cat mot ng chay xuong mc thap hn.Nguyen nhan co the la do viec thay oi kh hau danen viec gia tang tai trong hoac giam lu lng dongnc hay mc ay c s cua dong chay nang len, lamgiam o doc tao tram tch.- V nhng ly do tren, dong chay b nghen lai, bai boic nang cao dan, dan en tnh trang can bang bxao tron, t o dong chay bat au xam thc. Dongchay cat sau xuong long song, cat ngang qua ca cactram tch mi va lang ong. Dong chay mi namthap hn bai boi cu va tai ay dong nc tiep tucxam thc e hnh thanh bai boi mi. Lau dan, cac ditch cua bai boi cu con lu lai nh hai them ng trenbai boi mi. Hai them nam oi dien nahu cung mot

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o cao goi la them oi (paired terraces). oi khi songxam thc doc hnh thanh them n (unpaired terraces).

- Them song du la them n hay them oi eu co thecat vao a goc. Do vay, ngi ta thng gap aythem, tren a goc mot lp cat va cuoi mong.

6) Tac ong cua song oi vi xa hoi loai ngi:6.1/ Tac ong tch cc:- oi vi xa hoi loai ngi, cac dong song c xemla mot trong nhng nhan to hnh thanh nen nen vanminh nhan loai, la cai noi cua nen van minh nhan loai.Hau het cac nen van minh ln eu phat trien doctheo cac con song ln.VD:Nen van minh Lng Ha.Nen van minh Ai Cap: hnh thanh khu vc song Nile.Nen van minh lua nc khu vc ong Nam A: hnhthanh khu vc song Mekong.Nen van minh Trung Hoa: hnh thanh khu vc 2 song

Trng Giang va Hoang Ha.Nen van minh An o: hnh thanh khu vc 2 song Anva song Hang.- Cac song la mot trong nhng nguon cung cap ncngot (freshwater) chnh cho hoat ong song va san xuatcua con ngi. Ngoai ra, cac song con la nguon cungcap thc pham cho con ngi (cac loai thuy san).- Hoat ong boi tu cua cac dong song tao nen nhngong bang chau tho mau m phuc vu cho san xuatnong nghiep.- Cac song con la ni sinh song cua nhieu loai sinhvat, tao thanh nhieu he sinh thai a dang va ac sac.- Cac qua trnh song a tao nen cac canh quan vocung ac sac co y ngha quan trong trong hoat ong dulch va nghien cu.- Cac dong song con la cac tuyen ng giao thong,bien gii quoc gia

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- Cac dong song con gi vai tro ieu hoa thi tiet(nhiet o, o am , lng ma) trong mot pham vi giihan nhat nh.

6.2/ Tac ong tieu cc:

- Hoat ong xam thc cua song gay nen hien tngsat l ven b song, lam h hai cac cong trnh xay dng,e doa en tnh mang cua ngi dan.- Hoat ong boi tu khong ung cho cua song oi khicung gay nen tr ngai cho viec giao thong ng song.- Gay lu lut pha huy mua mang, cong trnh xay dng,gay thiet hai ve nhan mang.

B . LU :1) Khai niem ve lu:- Lu la hien tng nc song dang cao trong mot khoang

thi gian nhat nh, sau o giam dan. Trong mua ma lu,nhng tran ma tng t lien tiep tren lu vc song, lamcho nc song tng t noi tiep nhau dang cao, tao ra nhngtran lu trong song, suoi.- Vao cac thang mua ma co cac tran ma ln, cng omanh, nc ma tch luy nhanh, neu at tai cho a no ncth nc ma o ca vao dong chay, de gay ra lu. Khi luln, nc lu tran qua b song (e), chay vao nhng chotrung va gay ra ngap lut tren mot dien rong.- Lu ln va ac biet ln nhieu khi gay ra nhng thiet hai toln ve ngi va cua cai.

- Cha ong ta a xep lu, lut la mot trong nhng loai thien tainguy hiem nhat.- Mot dang khac cua lu la do hien tng v e, hay apcha nc hnh thanh lu.

2) Cac ac trng cua lu:Mc nc : la o cao cua mat nc trong song tnh tmot o cao chuan nao o ky hieu la H (cm).Lu toc dong va gradient cua dong.Lu lng nc: la lng nc chay qua mot mat catngang song trong mot n v thi gian, ky hieu Q (m3/s).Chan lu len: la lu bat au len (mc nc bat audang cao khi lu lng nc bat au tang len)

nh lu : la mc nc hay lu lng nc cao nhat trongmot tran lu.Chan lu xuong: la lu rut xuong thap nhat xap xbang luc bat au lu len.

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Thi gian lu len: la khoang thi gian t chan lu lenen nh lu.

Thi gian lu xuong: la khoang thi gian t nh luen chan lu xuong.Cng suat lu (m/h): la s bien oi cua mc nctrong mot n v thi gian.

3) Nhng yeu to anh hng en o ln (cng o)cua lu:* o tham loc cua cac loai vat lieu va at be mat: Moiloai at a eu co o xop va o tham loc khac nhau. atco o xop va o tham cao se cho phep mot lng ncln tham loc that nhanh xuong sau. Neu at a t tham thty le tham loc thap, ty le nc chay tren be mat giatang.

* a hnh: a hnh co anh hng rat ln en ty le cualng nc be mat. Khi trien co o doc cao nc chay trantren be mat gia tang va ch co mot lng nc that nhongam xuong. Do yeu to a hnh, ta thay lu khu vc thnglu va ha lu song cung co nhng ac iem khac nhau:

LU THNG LUSONG

- Ch xay ra trong mot khuvc khoang nam mikilomet doc theo mot dongsuoi hay cac song nho khu vc oi nui cao.- Thi gian xay ra rat nhanhchong.- Nguyen nhan: do cac cnma to khu vc thng lusong, hay do s v ap cuaho cha nc- Lng nc qua ln oap xuong song gay nenhien tng tran b, nhngsau o nhanh chong rutxuong ha lu.- Gradient dong chay ratcao, lu toc dong chay ln.- Hau qua: do sc chaymanh liet nen lu co thecuon troi nha ca, lam satl ng sa, h hai cac

cong trnh xay dng, gaythiet hai ve nhan mangnhieu hn lu ha lu song.

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LU HA LU SONG- Xay ra mot pham vitng oi rong: khu vcmot dong song hay khapkhu vc chau tho cua he

thong song.- Thi gian xay ra dai hn lu thng nguon.- Nguyen nhan: co the lado hau qua cua nhngtran ma to keo la nhieungay trong mot khu vcrong ln, oi khi la dotuyet tan hay do s ket hpgia ma va tuyet tan.

- Lng nc ln trai trenmot dien tch rong do cacsong b nghen ay nc.- Gradient dong chay ratthap, lu toc dong chay

thap.- Hau qua: lam chm ngapmot khu vc rong ln, gayh hai nen mong cong trnh,ngap ung cac khu vc canhtac, gay thiet hai ve nhanmang t hn lu thngnguon.

* Tham thc vat cung la mot trong cac yeu to anh hngen lu:- Cay co tao ra rao can oi vi nc chay tran lam chams di chuyen cua nc, lam giam ty le nc o vao songsuoi.- Re cay lam cho at ti xop, gia tang o tham lam ty lenc tham loc tang len, t o lam giam ty le nc bemat.- Cay co cung hap thu mot lng nc ln can cho s tangtrng. o cung la mot trong nhng yeu to lam giamlng nc ang ke o vao song suoi sau tran ma to.

* Viec khai pha ong lu va qua trnh o th hoa.

* Cac yeu to can bang khac: lu lut to mot so khu vctuy theo mua hay la hau qua cua s thay oi thi tiet.

3) Anh hng cua ca hoat ong nhan sinh oi vi lu:3.1/ Viec khai thac ong lu:* Nguyen nhan lam bien oi ong lu:- cac nc ang phat trien, dan so tang nhanh nencan co nhieu at e trong trot, ap ng nhu caulng thc cho ngi dan. at ong lu lai rat ph nhieuv hang nam lu lut em phu sa ve boi ap. Hn na ong lu co be mat rong ln nen cac cong trnh xaydng nha , kho tang, ng xa thuan li va rat retien. Chnh v the nen chang may choc nhieu thanhpho, trang trai moc len khap ni khu vc ong lu,lam cho no mat i vai tro ieu hoa lng nc d thatrong mua ma. Nhat la nhng nam co ma nhieu se

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tao ra lu lut nghiem trong, lam mat i tai san va sinhmang cua nhieu ngi.

* Hiem hoa do s phat trien ong lu:- S phat trien ong lu se dan en hai hau qua nguy

hiem sau: Tang lng nc va t le nc chay tran be mat.

Lam giam o tham va o xop cua dientch mat at.

2 yeu to nay a dan en s tang mc o nguyhiem cua cac cn lu.- Ngoai ra, viec xay dng nhieu cong trnh khu vcong lu cung lam gia tang chieu cao cua lu. V xaydng chiem mot the tch tng ng vi lng nctrc ay no chay vao nen lam chieu cao mc ncgia tang tng ng.

3.2/ Qua trnh o th hoa:- Viec xay dng thanh pho keo theo s hnh thanh cacvung phu can co anh hng ln en dong chay vamc o nguy hiem cua lu.- He thong ng trai nha, cac khoi be tong se gaycac anh hng sau:

Nc ngam xuong tang nc ngam giam trong khuvc co be mat b cong trnh xay dng che phu.Lu toc dong va lng nc tren mat tang.Mc nc di at ha v s tham loc giam.

- Anh hng tren dong chay c the hien cac yeuto:

Thi gian tre gia lng ma va nh lu rut nganv nc chay nhanh va nc ngam xuong at t.nh lu cao hn v dong chay mang nhieu nc hntrong khoang thi gian ngan v long song sach vathang.Lu lng c ban cua dong chay thap hn v nguoncung cap cho nc di at giam.

Hau qua chung cua s thay oi nay la dong chayot ngot co lu lng c ban thap va nh lu cao, thigian ngan.

4) Cac bien phap phong chong lu nguy hiem:4.1/ Cong tac d bao va quy hoach:- Bang phng phap thong ke n gian, chung ta cothe d oan c quy mo cua mot tran lut. Phng

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phap nay bao gom cac so lieu ve lu lng dong chaythu thap c t nhat trong 10 nam. Trc het, ta lendanh sach lu lng cc ai moi nam, ke o tien hanhsap xep lu lng cc ai t ln nhat en nho nhatva anh so lu lng ln nhat la so 1. ke o tnh

toan chu ky lut bang cong thc:

M

N R

)1( +=

(Vi R: chu ky lu; N la so nam cua so lieu; M la cng o.)

- Trong qua trnh quy hoach va thiet ke cau ng, caccong trnh xay dng, ngi thiet ke can xem xet khanang xay ra lu trong qua trnh thiet ke.- Khi thiet ke hay quy hoach, khong c v tiet kiem chi

ph xay dng ban au ma ch xem xet anh hng cualu en cong trnh mot cach ly tng.

4.2/ Thc hien cac bien phap nham tranh khonglam thay oi kha nang ieu tiet nc cua onglu:

- Tien hanh di di cac cong trnh, nha ra khoi khu vcnay.- Len ke hoach hng dong lu theo mot hng khac tthiet hai hn, to chc phong chong khu vc can cbao ve.

4.3/ Lam ho gi nc:- e tranh lu nguy hiem xay ra cac khu vc nam doctheo dong song, ngi ta xay dng ho cha nc. Honay la mot bon rong gi mot lng nc to khi coma lam giam lng nc chay vao song.- Ho thng c xay dng vung ma trc o akhai thac khoang san b bo hoang. Thong thng bangcach ap ap at ngan nc ni at t co gia trs dung. Hn na khu vc xay ho khong lam bien oimoi trng can bang cua dong song.

4.4/ Khi dong:- La cach lam thay oi dong song ve lu toc hoac lulng hoac ca hai, ket qua la nc nhanh chong thoati.- M rong va vet sau long song, ac biet la nhngni at yeu de b xam thc, b song se b sat l,ay song nhanh chong b can i.

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- Can gia co b song vng chac.- ao nhng oan song mi cat qua khuc uon e lamsong chay thang tr lai cac khuc quanh co, giupthoat nc nhanh hn.

4.5/ He thong e ieu:- e tranh nc lu len cao tran ngap mot so khu vc,ngi ta ap e hai b song e ngan chan.- Tan dung he thong e t nhien.- e gi nc long song khong cho tran vao onglu, tuy nhien hau qua la nc se don ve pha ha lunhanh chong. Khi lu lng nc song qua ln se danen tnh trang lu lut nguy hiem ha lu.

4.6/ Bien phap khac:- Bien phap trong rng, cai tao rng.

Khoanh nuoi phuc hoi rng ni co the tai sinh. Trong rng ni at trong oi troc.- Chung song vi lu.

5) Lu lut Viet nam:5.1/ Phan loai:- Nc ta nam vung kh hau nhiet i am, gio muanen lu do ma sinh ra bao gom cac loai sau:

Lu tren cac song, suoi va va nho: xay ratrong thi gian ngan va thng la lu quet.

Lu tren cac song ln: xay ra trong thi giandai, toc o lu cham.

Lu tieu man, lu sm, lu chnh vu, lu cuoivu.

- Ngoai ra can c vao mc nc nh lu, ngi ta chia racac loai lu sau:

Lu nho, lu va.Lu ln.Lu ac biet ln.Lu lch s.

5.2/ Mua lu:- Vung Bac bo : mua lu t thang 5,6 en thang 9,10. Tay Bac va ong Bac thng xay ra vao thang 5 ketthuc thang 9.Song Hong va cac nhanh song ln: song a, Thao, Loxay ra vao thang 6 ket thuc vao thang 10, cao nhat vaothang 7,8.- Bac Trung Bo : t thang 6,7 en thang 10,11.

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- Nam Trung Bo : keo dai t thang 10-12.- Tay Nguyen : thang 6, 7 en 11 xay ra bac TayNguyen

Thang 8,9 en 12 trung Tay Nguyen. Thang 7-11 Nam Tay Nguyen.

- ong va Tay Nam Bo : xay ra vao thang 7-11.5.3/ Nguyen nhan:- Cc hnh th gy ma l:* Trn lu vc sng Hng : nhng hnh th thi tit ch yu gy ra mal thng l: di hi t nhit i, cao p Thi Bnh Dng, xoy thun nhiti (bo, p thp nhit i), khng kh lnh,* Cc lu vc sng Min Trung: gm 3 loi chnh

Bo, p thp nhit i hoc bo, p thp nhit i kt hp vi khngkh lnh:khng kh lnh kt hp vi p thp nhit i, bo, p thp di hi t

nhit i,Di hi t nhit i kt hp vi khng kh lnh hoc cc hnh thkhc.

* Trn lu vc sng MKng: hng nm t thng 5 lu vc sngMkng chu nh hng ngy cng tng ca gi ma ty nam, mang m tbin n, mnh nht vo cc thng 8, 9,10. do cc hot ng nhiu ngca thi tit nh di hi t nhit i c bit l bo bin ng gy maln pha Ty Trng Sn dn n l sng Mkng.

5.4/ Dien bien:* Mien Bac:

L, lt ng bng Bc B l hu qu ca cc t ma trn luvc ca 2 h thng sng Hng v sng Thi Bnh.L ln nht ca sng Hng xut hin sm nht vo ngy 09/07/1964v xut hin mun nht vo ngy 13/09/1979, nhng c trn 50% lxut hin vo thng 8.Ngoi ra ngp lt ng bng Bc B cn nh hng n h thng.

* Mien Trung:Do dc ln sng min Trung ngn, ng bng thp,

ca tiu thot hp hoc khng thun.Cc tuyn ng st, ng b ct ngang qua hng chy

to nn nhng ng ngn l kt hp vi ma ln tng t nn ltp trung nhanh, c ma l c l.

L ln nhanh nhng rt chm do nh hng thu triu vcc ng ngn l nn ngp lt rt su cc vng ng bng hpng dn c.

* Mien Nam:

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- BSCL l mt vng bng phng, c th phn thnh 4 vng.Di t cao ven bin ng (Bn Tre, Tr Vinh, Sc Trng, Bc Liu): cao trung bnh 2-3m c nhiu sng chy qua nhng khng bngp lt do l sng.Vng trng ng Thp Mi (Pha t sng Tin t Bc Tin Giang

n bin gii Vit Nam-Campuchia): cao mt t trn 2m ni thp0.5m xung quanh c bao bc bi b bin G Cng, b sng Tinv thm t c ng nam b nn thng xuyn b ngp lt.Vng T Gic Long Xuyn (nm pha hu sng Hu pha trn rchCi Sn): c cao mt t thp v dc nghing t b sng Husang vnh Kin Giang nn thng xuyn ngp lt.Vng t thp v chua mn U Minh C Mau : c cao thp xongdo st mt bin nn bi ngp lt bi nc sng v ch b ngp mn.

5) Lu quet:- Lu quet la mot hien tng thien tai co tnh chat va aciem khac biet la lu dien bien nhanh, mang tnh bat thanva khoc liet, moi tran xay ra tren mot dien hep va phamvi tac ong cung hep hn lu song.- Neu ma ln, nc ma lai b tch luy bi cac trng ngaivat nh at a, cay coi cho en khi lng nc vt quasc chu ng cua vat chan, pha v vat chan, ao xuongcap tap (rat nhanh), cuon theo at a, cay coi va quet imoi vat co the quet theo dong chay th c goi la lu quet(hay lu ong), thng dien ra rat nhanh, khoang 3-6 gi.- Lu quet xay ra bat ng, nhanh, co sc tan pha ln cac lu vc nho. Tieng Anh lu la flood, lu quet la flash flood(flash la vut hien roi tat), tieng Trung Quoc lu la "hongthuy", ngha la "nc ln".- Trong mot so trng hp no co sc tan pha khung khiepva tr thanh tham hoa t nhien, nh tran lu quet nam 1998 th xa Lai chau (cu) a xoa so ca ban Mng Lay va khuvc th xa. Lu thng xay ra vung nui, ni co a hnh oinui cao xen ke vi thung lung va song suoi thap.- Lu quet tam thi co the phan chia lam 3 loai:+ Lu gay ra do ma a phng, tap trung ln cac lu vc t nhien (hau nh cha co tac ong cua con ngi);+ Lu gay ra do ma ln tren cac lu vc a chu tac ongmanh cua cac hoat ong kinh te cua con ngi lam mat onnh hay pha v can bang sinh thai lu vc (thay oi lpphu, che o dong chay, lng tr hay cac ac tnh luvc);+ Lu gay ra do thao, v thnh lnh mot lng nc tch do vap chan hay cac ap gi nc, cac ap bang...- Lu quet thng gay hoa cho cac song nho va va nhng toi vi song ln. cac lu vc song suoi nho mien nui,

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ni co ieu kien thuan li e hnh thanh lu quet nh: ahnh chia cat, o doc lu vc va o doc long song/suoi ln,o on nh cua lp at tren be mat lu vc yeu do quatrnh phong hoa manh, lp phu thc vat b tan pha nhng ni nay, khi ma ln, tap trung trong mot thi gian

ngan th xay ra lu quet.

Song va lu

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