ĐẶc ĐiỂm chẾ ĐỘ dÒng chẢy vÀ chẤt lƯỢng...

Qun l ti nguyn rng & Mi trng

49TP CH KHOA HC V CNG NGH LM NGHIP S 2-2015

C IM CH DNG CHY V CHT LNG NC CA LU VC RNG TRNG TI NI LUT, XUN MAI, H NI

Bi Xun Dng1, Ph Th Hi Ninh2, Kiu Th Dng3, L Thi Sn4 1TS. Trng i hc Lm nghip 2,3ThS. Trng i hc Lm nghip 4KS. Trng i hc Lm nghip

TM TT

Rng ng vai tr quan trng trong vic iu tit dng chy v bo v ngun nc. Tuy nhin, nhng nghin cu v c im dng chy v kh nng bo v ngun nc ca cc kiu rng trng nc ta cn hn ch. Nhm gp phn tm ra quy lut dng chy v cht lng nc ca lu vc rng trng, nhm tc gi tin hnh quan st c im dng chy v cht lng nc cho lu vc rng trng u ngun ti ni Lut, Xun Mai, H Ni trong giai on 1: t 9/2011 n 6/2012 nh gi ch dng chy v giai on 2: t 6/2014 n 9/2014 nhm nh gi ch dng chy v cht lng nc lu vc. Phng php phn chia biu thy vn c s dng nhm tm ra quy lut ng i ca dng chy, trong khi cc phng php phn tch thng k c s dng nhm tm ra c trng dng chy v cht lng nc ca lu vc. Kt qu nghin cu chnh ch ra rng: (1) Dng chy phn ng tng i nhanh so vi ma, khi lng ma ln nht th dng chy ngay sau cng t gi tr ln nht; (2) H s dng chy lu vc cho cc trn ma l tng i ln, trung bnh 74%; (3) Dng chy u th trong lu vc rng trng l dng chy t nn t (chim 55%), trong khi dng chy b mt t chim 45% tng dng chy lu vc; (4) Cht lng nc t lu vc rng trng l tng i tt. Cc ch tiu pH, SS, DO, Cl-, NO2-, SO42- u nm trong tiu chun cho php.

T kha: Cht lng nc, dng chy lu vc, dng chy mt, dng chy nn t, lu vc rng trng, phn chia biu thy vn.

I. T VN Nc l mt dng ti nguyn quan trng v

cn thit cho s tn ti v pht trin ca cc h sinh thi v con ngi c hai khu vc c rng v khng c rng (FAO, 2005). Trong khi , tr lng v cht lng nc ngt trn th gii ang ngy cng b e da bi vic khai thc ba bi, s dng qu mc v nhim (Marzocchi et al., 2009). V vy, vic bo v ngun nc ngt c t ra cp thit nhm bo tn s sng trn tri t. Rng c mi quan h cht ch vi cc ngun ti nguyn nc v rng duy tr cht lng nc thng qua s n nh ca t, gim thiu xi mn, by trm tch v cht gy nhim t cc vng t dc (FAO, 2005). Rng cng nh hng n tr lng nc c sn bng vic gi li mt lng nc ma trn tn, bc hi m t b mt thc vt, duy tr m ca t, thu nc sng m v duy tr tc thm ca t. Rng ng thi nh hng n

thi gian vn chuyn nc bng cch duy tr hoc ci thin thm v kh nng tch ly nc trong t (Bosch v Hewlett, 1982). Do , qun l ti nguyn rng c mi lin quan cht ch n qun l ti nguyn nc v bo tn t thng qua vic thay i s lng, thi gian nc chy mt v xi mn t (FAO, 2005). Trong s cc loi rng khc nhau, rng trng v rng th sinh chim a s rng trn th gii. Khong 3,2 triu ha tng ng vi 24 % din tch rng ca Vit Nam l rng trng (B Nng Nghip v Pht trin nng thn, 2012). Din tch rng trng c xu hng tng ln hng nm (B Nng Nghip v Pht trin nng thn, 2012). Rng trng ca Vit Nam c trng khng ch s dng cho mc ch thng mi m cn phc v cho chc nng phng h u ngun. Bi rng c chc nng bo v t chng xi mn, iu tit dng chy v duy tr cht lng nc. Mc d chc nng ny c


50 TP CH KHOA HC V CNG NGH LM NGHIP S 2-2015

tha nhn rng ri trn th gii cng nh Vit Nam, tuy nhin s thiu ht c s d liu phn nh mi quan h gia rng trng vi ch dng chy cng nh cht lng nc ti Vit nam l tr ngi ln trong vn xy dng cc m hnh rng trng ph hp nhm em li hiu qu mi trng tt nht.

Rng trng ti Ni Lut trng i hc Lm nghip c hnh thnh t nhng nm 1984 v cho n nay tr thnh mt h sinh thi rng phong ph v chng loi, c gi tr v c ngha thc tin phc v cng tc nghin cu v o to ca nh trng. Bn cnh , h sinh thi rng trng cn c vai tr quan trng trong vic iu tit dng chy v ci thin cht lng nc cho khu vc. Nhm gp phn lm sng t vn ny, chng ti tin hnh nghin cu c im ch dng chy v cht lng nc ca lu vc trong khu vc ny. Cc kt qu nghin cu c nu tm tt trong bi bo ny. Kt qu ny cung cp c s khoa hc quan trng nhm nng cao chc nng phng h ca rng trng Vit Nam.

II. PHNG PHP NGHIN CU

2.1. i tng nghin cu

c im ch dng chy v cht lng nc thng qua vic nh gi mt s ch tiu: SS, pH, DO, Cl-, SO42- v NO2- ti lu vc rng trng ti ni Lut, trng i hc Lm Nghip.

2.2. Phng php nghin cu 2.2.1. Nghin cu c im ch ma

Lng ma c thu thp ti lu kh tng thy vn rng ca trng i hc Lm Nghip. S liu thu thp gm lng ma hng gi t nm 1997 n nm 2013. Ngoi ra, s liu ma cn c iu tra b sung ti cc thi im khc nhau bng thit b o ma t ng (tipping bucket rain gauge) cho cc trn ma vi thi gian o l 5 pht mt ln cho cc trn

ma khc nhau. S liu thu thp s c phn tch nh gi nhm tm ra c im ch ma v nh gi phn ng ca dng chy theo cc trn ma khc nhau ti khu vc nghin cu. S liu ma c o theo phng php t ng l 15 trn ma khc nhau.

2.2.2. Nghin cu c im ch dng chy

Cc ch tiu dng nh gi ch dng chy ca lu vc bao gm dng chy ln nht, dng chy nh nht, phn hi ca dng chy vi cc trn ma, v cc qu trnh dng chy nh dng chy mt v dng chy di nn t.

S liu dng chy lu vc c xc nh thng qua mng o dng chy v thit b o mc nc cao mc nc t ng. Mc nc ca dng chy c lu gi t ng trong 5 pht mt ln ghi. Da vo mc nc ca dng chy chng ti xc nh c sn lng dng chy lu vc cho mi trn ma, cho thng v cho nm. Thi gian quan trc c thc hin lm 2 giai on: giai on 1: t 9/2011 n 6/2012, giai on 2: tin hnh t 6/2014 n 9/2014. Dng chy lu vc c o bng mng tn v thit b o mc nc t ng (water level logger) (Hnh 01). Theo cch ny, ton b dng chy lu vc s c chy qua mng tn. Mc nc trong mng tn s t ng c ghi li 5 pht mt ln. Da vo mc nc , chng ta c th tnh c lu lng dng chy cho lu vc thng qua phng trnh thc nghim.

S liu thu thp c sau s dng xc nh ng i dng chy thng qua vic phn chia thnh cc thnh phn dng chy nh dng chy nhanh v dng chy chm bng phng php phn chia biu thy vn ca Hewlett and Hibbert (1967). y, dng chy nhanh ch yu c ng gp bi dng chy b mt, trong khi dng chy chm c hnh thnh ch yu bi dng chy trong nn t.



Hnh 01. Mng tn dng o dng chy v

cht lng nc lu vc

Biu 01. Biu m t phng php phn chia thnh phn dng chy

Theo phng php ca Hewlett and Hibbert (1967), ng phn chia thy vn c dng: y = a.Time + b. Trong : a l hng s. Ty theo khong thi gian s dng (pht, gi, ngy) phn chia m c hng s a tng ng. Vi trng hp s dng l 5 pht phn chia, hng s a=1.32x10-5; b l gi tr dng chy trc im phn chia u tin. Time l thi gian phn chia (trong nghin cu ny l 5 pht). Phng php nghin cu ny c m t c th ti biu 01.

2.2.3. Nghin cu c im cht lng nc ca lu vc

Cc ch tiu vt l v ch tiu ha hc c s dng nh gi c im cht lng nc lu vc bao gm pH, hm lng sulfate, hm lng Nitrite, Chlorine, cht rn l lng v lng oxy ha tan (DO). Cc mu nc c thu thp cho mt s trn ma din ra ti khu vc nghin cu. Phng php thu thp c th c trnh by nh sau:

+ Phng php o pH: pH c o bng giy qu v so vi bng mu.

+ Cht l lng (Suspend sediment -SS): mu nc c ly ti cc trn ma khc nhau c mang v phng s dng giy lc v my sy xc nh lng cht rn l lng;

+ Lng oxy ha tan trong nc (DO), nng Chloride, nitritae and sulfate: lng xy ha tan trong nc c xc nh da vo thit b o nhanh (Test kit model FF-1A) cho cc thi im khc nhau ca cc trn ma (Hnh 02);

Hnh 02. B thit b kim tra nhanh cht lng nc ti khu vc nghin cu

Tng s mu c xc nh ly v phn tch cc ch tiu nc l 50 mu cho 9 trn ma khc nhau ngoi thc a.

III. KT QU NGHIN CU V THO LUN 3.1. c im ch ma ti khu vc nghin cu

Khu vc nghin cu thuc tiu vng kh hu 3 ca min Bc Vit Nam, hng nm c 2 ma r rt: ma ma thng bt u t thng 4 n thng 10, ma kh bt u t thng 11 n thng 3 nm sau.

Dn

g ch

y l

u v

c(m

m)

Thi gian (T- pht)

Dng chy nhanh

Dng chy chm

Trn ma

ng phn chia

bTimeaY *

(Hewlett and Hibbert, 1967)



S liu quan trc ma 14 nm lin tc t nm 1995 ti nm 2008 ti trm quan trc kh tng ca Trng i hc Lm nghip c tng hp ti biu 03. Da vo b s liu cho bit, ti khu vc nghin cu lng ma bnh qun hng nm 1700 mm/nm. Nm c lng ma ln nht l 1996 vi lng ma ln ti 2300 mm/nm, trong khi nm c lng ma nh nht l nm 1995 vi ch 1300 mm/nm.

0

50

100

150

200

250

300

350

1 2 3 4 5 6 7 8 9 10 11 12

L

ng m

a

(mm

/thn

g)

Thng

Biu 02. c im lng ma hng thng trong ca ti lu vc

Thng c lng ma ln nht l thng 7, trung bnh 304 mm/thng (dao ng t 115 ti 578 mm/nm). Thng c lng ma nh nht l thng 1 vi lng ma trung bnh l 14 mm/thng (bin dao ng t 0-45

mm/thng). Cc thng ma ma t thng 4 ti thng 10 chim 89% tng lng ma hng nm ca khu vc (Biu 02). V vy vic nghin cu ch dng chy v cht lng nc c thc hin trong nhng thng ny l rt cn thit. 3.2. c im ch dng chy ti khu vc nghin cu 3.2.1. Phn ng ca dng chy i vi cc trn ma

Dng chy hng ngy ca lu vc phn ng rt nhanh vi lng ma (Biu 03). Khi lng ma hng ngy tng th dng dng chy lu vc cng tng. Khi ma kt thc dng chy cng rt nhanh chng suy gim m khng hnh thnh nh l tip theo. Thi gian tr (khong thi gian tnh t lc ma ln nht n dng chy ln nht) l tng i nh hu ht cc trn ma. Tuy nhin nh l c xu hng ln hn khi ch s ma hai ngy ma trc (API2) ln hn v ngc li (Biu 04). iu ny c th gii thch rng khi ch s ma hai ngy trc nh s lm t kh hn (lng nc trong t t), v vy khi ma xung nc s c xu hng thm nhiu xung t hn l to ra dng chy mt.

Biu 03. Phn ng ca dng chy lu vc vi lng ma

16.2mm

53.6mm54.8mm

18mm

29.6mm

39mm

0

0.05

0.1

0.15

0.2

0 5 10 15 20

Pe

ak fl

ow

(mm

5m

in-1

)

API2 (mm) Biu 04. Xu hng quan h gia nh l v

ch s ma trc 2 ngy (API2)

0

20

40

60

80

100

Daily

rain

fall (

mm

)

0

10

20

30

40

50

Daily

runo

ff (m

m)

Ln

g m

a h

ng

ngy

(mm

)D

ng ch

y h

ng

ngy

(mm

)

2011 2012

nh l

(mm/5

pht)



3.2.2. c im v thnh phn dng chy Kt qu phn tch 15 trn ma (Biu 05)

cho thy, vi nhng trn ma ln tng ng c c dng chy ln. C th trn ma ln nht ln n 400 mm, trong khi trn ma nh nht l 14 mm (Biu 05a). Dng chy ca lu vc tng ng l 346 mm v 0,02 mm (Biu 05b). H s dng chy lu vc (dng chy lu vc chia cho lng ma) dao ng t 0.1 n 97% (Biu 05c). iu ny ch ra rng

nhng lu vc quy m nh, dng chy theo ma th hu ht lng ma u chuyn thnh dng chy lu vc.

Dng chy lu vc c quan h rt cht so vi lng ma (Biu 06) theo hm tuyn tnh. Khi lng ma tng th dng chy lu vc ng thi tng theo. Phng trnh quan h ca chng c th hin qua dng: y= 0,9319x 6,174. H s xc nh ca phng trnh:

R2= 0,9904 (Biu 05). 0

100

200

300

400L

ng

m

a (m

m/tr

n)

0

100

200

300

400

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Dn

g ch

y l

u v

c(m

m)

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

H

s d

ng

chy

(%)

Trn ma

(a)

(b)

(c)

Biu 05. c im ma (a), dng chy lu vc (b) v h s dng chy lu vc (c) theo trn ma

Da vo phng php phn tch v phn chia biu thy vn (Hewlett and Hibbert, 1967) cho 13 trn ma khc nhau, kt qu phn nh thnh phn dng chy chnh gp phn hnh thnh dng chy lu vc l dng chy chm (Biu 07). Dng chy chm chim t 16 n 100%, trung bnh l 55% dng chy lu vc, trong khi dng chy nhanh dao ng t 0 n 84%, trung bnh 45% dng chy ca lu vc. Kt qu ny ch ra rng

thnh phn dng chy ti lu vc rng a s l dng chy nn t. iu ny m bo cho vai tr iu tit dng chy v hn ch xi mn t cc h sinh thi rng. Tuy nhin, dng chy nhanh, thnh phn ng gp t dng chy b mt t, cng chim t l tng i ln, n 45%. iu ny cng phn nh nguy c xi mn c th xy ra di h sinh thi rng trng nghin cu.



Biu 06. Quan h gia lng ma

v dng chy lu vc

0

20

40

60

80

100

120

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Thn

h ph

n d

ng

chy

(%

)

Trn ma

Dng chy nhanh Dng chy chm

TB

Biu 07. Thnh phn dng chy ng gp vo dng chy lu vc

3.3. c im cht lng nc ca dng chy lu vc 3.3.1. Cht l lng (SS)

3.28

9.893.78 5.88

78.24

96.86

23.75

63.34

36.05

0

20

40

60

80

100

120

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9

Ma

Cht l lng

Trn ma

Lng ma (mm) Cht l lng

(mg/L)

Biu 08. c im cht l lng v ma ti

lu vc nghin cu

11.73

35.3313.49 21.01

279.53

346.07

84.87

226.30

128.78

0

20

40

60

80

100

120

0

50

100

150

200

250

300

350

400

1 2 3 4 5 6 7 8 9

Dng ch y

Cht l lng

Trn ma

Lu lng dng chy (mm)

Cht l lng (mg/L)

Biu 09. c im dng chy

v cht l lng

Kt qu quan st trn 9 trn ma v dng dng chy khc nhau cho thy, lng rn l lng dao ng t 3,27 mg/l ti 96,86 mg/l, trung bnh t 35,67 mg/l. Hm lng cht rn l lng c xu hng gia tng khi lng ma gia tng (Biu 08) v dng chy lu vc gia tng (Biu 09). Khi lng ma gia tng, cht l lng cng gia tng. C th trn ma c lng ma ln nht l 399 mm th tng cht l lng cng ln nht t 97 mg/l (Biu 08). Tuy nhin, tng lng cht l lng ca tt c cc trn ma quan st u nm di ngng cho php so vi tiu chun nc nui trng thy sn (100 mg/l).

Hm lng cht rn l lng c quan h rt cht vi lng ma, iu ny c th hin qua phng trnh: y = 0,2526x + 0,8228 vi h s xc nh R2 = 0,9948 (Biu 10). Trong khi quan h gia cht rn l lng v dng chy lu vc c th hin qua phng trnh: y = 0,2799x - 10-14. H s xc nh l R2 = 1 (Biu 10). Kt qu ny phn nh s ph thuc rt cht ch ca cht l lng vo lng ma v dng chy lu vc. M hnh tm kim c s l cng c tt d bo lng cht rn l lng da vo lng ma v dng chy lu vc t lu vc rng trng.

y = 0.9319x - 6.174R = 0.9904

0

50

100

150

200

250

300

350

400

0 100 200 300 400 500

Dn

g ch

y l

u v

c (m

m/tr

n m

a)

Lng ma (mm/trn)



y = 0.2799x - 1E-14R = 1

0

20

40

60

80

100

120

0 100 200 300 400 500

Tn

g ch

t l

lng

(mg/

l)

Dng chy lu vc (mm/trn ma)

y = 0.2526x + 0.8228R = 0.9948

0

20

40

60

80

100

120

0 100 200 300 400 500

Tn

g ch

t l

lng

(m

g/l)

Lng ma (mm/trn ma) Biu 10. Quan h gia cht l lng vi lng ma v dng chy lu vc

3.3.2. Lng oxy ha tan (DO-mg/l) Nng oxy ha tan trong dng chy lu

vc xc nh 9 trn ma quan st dao ng t 7,1 ti 7,9 mg/L, trung bnh t 7,4 mg/L, m

bo tiu chun cht lng nc cho nui trng thy sn (DO yu cu 4 mg/L). Ngoi ra, hm lng oxy ha tan trong nc c xu hng ln hn khi lng ma ln (Biu 11).

6.6

6.8

7

7.2

7.4

7.6

7.8

8

0

50

100

150

200

250

300

350

400

450

1 2 3 4 5 6 7 8 9

Lng ma

DO(mg/L)

DO

(mg/L

)L

ng m

a

(m

m)

Trn ma

Biu 11. c im lng oxy ha tan ca dng chy lu vc v lng ma

3.3.3. pH

0

1

2

3

4

5

6

7

8

9

1 2 3 4 5 6 7 8 9

pH

QCVN 01:2009/BHYT

QCVN 01:2009/BHYT

Storm event

0

50

100

150

200

250

300

350

400

450

Rainfall

Rainfall

mm/storm

Trn ma

L

ngm

a

(mm

)

pH

Trn ma Biu 12. pH v lng ma theo thi gian



Kt qu phn tch pH ca 9 trn ma khc nhau cho thy, gi tr pH ln nht l 7.5 v gi tr thp nht l 7 (Biu 12). Tt c cc gi tr pH ca cc trn ma u nm trong ngng cho php ca nc dng cho n ung (pH=6.5-8.5), trong tiu chun mi trng Vit nam. Nu da vo pH nh gi th cht lng nc trong lu vc rng nghin cu m bo v c th p ng c cho nhiu mc ch khc nhau ca con ngi. 3.3.4. Chloride (Cl-), sulfate (SO42-) v nitrite (NO2)

Tt c cc gi tr ca Chloride u l 37.5 mg/l v nh hn rt nhiu ln so vi tiu chun cho php (Bng 01 v 02). Khng c s khc bit Chloride khi c s thay i ca lng ma. Ngoi ra, cc ch tiu sulfate and nitrite tt c cc ln o cho 9 trn ma khc nhau u nm trong ngng cho php ca tiu chun nc cho nui trng thy sn v khng c bin ng theo trn ma. iu ny ch ra rng nc t lu vc rng l tt v c th s dng cho nhiu mc ch khc nhau nh n ung, nui trng thy sn.

Bng 01. Nng cc cht chloride, sulfate v nitrite trong dng chy

Parameters 1 2 3 4 5 6 7 8 9

SO4(mg/L)



ma ma nn cc s liu v cht lng nc phn nh thi k cht lng nc km nht ca lu vc. iu ny cng khng nh cht lng nc t lu vc nghin cu.

Mc d c gng thc hin nghin cu, s liu thu thp c cha lin tc cho thi gian di v vy cha khi qut ha c quy lut dng chy v cht lng nc cho chu k hng nm. khc phc c nhng tn ti nu trn, cc ti tip theo cn tp trung nghin cu vi s liu thu thp di (t nht l hn 1 nm s liu). TI LIU THAM KHO

1. Bosch JM, Hewlett JD. 1982. A review of catchment experiments to determine the effects of vegetation changes on water yield and evapotranspiration. Journal of Hydrology 55: 323.

2. B Nng nghip v pht trin nng thn. 2012. Quyt nh s: 2089/Q-BNN-TCLN v vic cng b din tch rng ton quc nm 2011.

3. Hewlett JD, Hibbert AR. 1967. Factors affecting the response of small watersheds to precipitation in humid areas, in: Sopper, W.E., Lull, H.W. (Eds.), Intl. Symp. For. Hydrol. Pergamon, New York, pp. 275-290.

4. FAO (The Food and Agriculture Organization of the United Nations). 2005. Forest and floods: Drowning in fiction or thriving on facts. ISPN 979-3361-64-6.

5. Marzocchi W, Mastellone ML, Di Ruocco A, Novelli P, Romeo E, Gasparini P. 2009. Principle of multi-risk assessment: Interaction amongst natural and man-induced risks. European Commission, Directorate-General for Research Communication Unit. B-1049 Brussels.

CHARACTERISTICS OF FLOW REGIME AND WATER QUALITY FROM

FORESTED CATCHMENT AT LUOT MOUNTAIN, XUAN MAI, HANOI Bui Xuan Dung, Phi Thi Hai Ninh, Kieu Thi Duong, Le Thai Son

SUMMARY Forests play an important role in regulating the flow and protection of water resources. However, the research on flow characteristics and the ability to protect water resources of the plantation forest in Vietnam is limited. To evaluate the flow regime and water quality in the plantation catchment, we have observed the characteristics of flow and water quality in forested headwater catchment at Luot mountain, Xuan Mai, Hanoi during two periods: from September 2011 to June 2012 to analyze the flow regime; and from June to September, 2014 to clarify the flow regime and water quality. Hydrograph separation analysis methods was used to find out flow pathway, while the statistical analysis method is used to find out the characteristics of flow and water quality in the catchment. Results of the study indicate that: (1) Catchment runoff response quickly to precipitation input.. Higher precipitation get higher catchment runoff immediately; (2) Runoff coefficient of storm events is relatively high, averaging 74%; (3) Dorminant runoff pathway is subsurface flow, occuppied to 55% of catchment runoff, while surface runoff accounts for 45%; (4) The quality of water from the catchment is relatively good. The target pH, SS, DO, Cl-, NO2-, SO42- are within permissible standards.

Keywords: Catchment runoff, forested catchment, hydrograph separation analysis, overland flow, subsurface flow, water quality.

Ngi phn bin : PGS.TS. Phng Vn Khoa Ngy nhn bi : 25/02/2015 Ngy phn bin : 14/4/2015 Ngy quyt nh ng : 09/6/2015

ĐẶc ĐiỂm chẾ ĐỘ dÒng chẢy vÀ chẤt lƯỢng...

Documents