An Investigation of How Discharge Influences the Amount and Size of the Bed Load of the Negro River

8/18/2019 An Investigation of How Discharge Influences the Amount and Size of the Bed Load of the Negro River

http://slidepdf.com/reader/full/an-investigation-of-how-discharge-influences-the-amount-and-size-of-the-bed 1/17



*t has been shown that the discharge along with the bed load of a





n Februar the #/th )$#)0 the courses of the Negro River in St.

Thomas Jamaica were visited0 from its u!!er course in Cedar 1alle to its middle course

in New 2on3 4and and finall its lower courses in 5anvers 6en and &or3. The river was

visited during the late morning and earl afternoon. At this time the river was in its low

!ea3 flow stage. *t was at these !oints where several measurements were done in order to

collect the !rimar data needed to com!lete this *.A. Such measurements included the

cross sectional area of each course along with the velocit of the course. Sam!les of the

bed load were also collected and analzed.

The velocit was calculated b choosing a s!ecific distance in the river channel

for each courses and allowing a ball to flow from on !oint of the distance chosen to the

ne(t and the time for this recorded. This was done several times in order to get an average

time for the balls 7ourne.

The cross sectional area was calculated b measuring the width and average de!th

of the river channel. The width was measured b stretching on end of the ta!e measure

from one ban3 of the river to the ne(t and the distance obtained recorded. The de!th was

calculated b using the meter rule and the ta!e measure. The ta!e measure was stretched

horizontall across the river channel and the rule !lace in the water and the de!th at

different intervals +#$cm in Cedar 1alle0 #$cm in New 2on3land0 $.%m in 5anvers 6en,

on the ta!e measure recorded.

)$ random stones were ta3en from the bed load at each course of the river and the

width and length of each measured. This was done to determine the various changes in

the size of the bed load as it goes downstream.





The Negro river is located on the south coast of Jamaica in the !arish of St. Thomas. The

source of the river is located within the 8lue 2ountains. The river has latitude of #9.;

degrees and longitude of <9/./% degrees. The stream is 9%3m east of the a!!ro(imate

centre of Jamaica and #3m east of the countr-s ca!ital =ingston. The drainage basin

size of the river is a!!ro(imatel #/$3m s>uared and has an average height of ))% meters

above sea level. The river 7oins the larger ?est Arm of the 2orant River in Seaforth

which later em!ties into the sea at 2orant 8a.

Characteristics of the River Valley at different points along its course

Cedar 1alle



This area can be considered as the u!!er course of the river valle due to several

factors. Such factors include:

#. The sizes of the bed load in the river. The materials !resent at Cedar 1alle

averaged sizes of those similar to boulders. Average sizes included the long a(is

of the material being 9.%cm and the short a(is being %.cm. These figures

re!resent the average sizes of the bed load material in the u!!er course of a river.

Figure ) shows the boulder size materials at cedar valle with the u!!er course of

the river.

Figure ) shows the boulder li3e materials !resent at cedar valle.

). The width and de!th of the river. The width of the river was found to be ver

narrow at Cedar 1alle and the de!th was found to be shallow in this area as well.

These factors are characteristics of an t!ical river ma3ing this area the u!!er

course of the river.

@. The flow of the river. At this !oint of the river turbulent flow was !resent. This

t!e of flow is mainl !resent in the u!!er course of a river channel. This t!e of

flow can be shown in figure @ below.

8oulder

size

materiasl



Figure @ shows turbulent flow of the river at Cedar 1alle.

. The gradient of the valle sides. The gradient of the valle sides in the area we

found to be ver stee!. Stee! valle sides are found in the u!!er course of a river.

Figure below show s the stee! valle sides of the river.

New Monkland

Turbulentflow

Stee! 1allesides



Newmon3 land shared similar characteristics to that of Cedar 1alle0 this ma3e the

area a !art of the rivers u!!er course. Similarl the area had:

#. The area had boulder size bed load materials !resent as well in the river channel

averaging size n the long a(is of 9cm and short a(is of /cm. figure % shows the

boulder size materials !resent in the river channel at New 2on3land.

Figure % shows the bed load materials !resent in New 2on3land.

). The width and the de!th of the river channel in this area were similar to that of

Cedar valle. The width of the river channel was narrow and the de!th shallow.

@. Turbulent flow was also !resent in this area as it was also !resent in cedar valle.

Figure / below shows turbulent flow within the river channel.

8oulder size bed load



Figure / shows turbulent flow in the New 2on3land area of the river channel.

. The gradient of the valle sides. At this location the valle sides were found to be

relativel stee!. Stee! valle sides are found in the u!!er course of a river.

Danvers Pen

This area can be considered the middle course of the river due to several factors. Such

factors include:

#. The sizes of the bed load materials. The bed load had decreased in size and was

now averaging sizes of stones and gravel. Theses sizes are normall found in the

middle course of a t!ical river valle. Figure 9 below shows the stone and gravel

size materials !resent in the river channel.

Turbulent

flow



Figure 9 shows the materials !resent at 5anvers 6en.

). The width and de!th of the river valle. The width of the river valle had become

widen becoming almost broad. The de!th had changed as well0 becoming less shallow

to near dee!. Figure ; below shows the widen width of the river channel in 5anvers

6enn.

Figure ; shows the widen river channel in 5anvers 6en.

Bravel and stone

size materials

?iden riverchannel.



@. The flow of the river at. At this !oint the flow of the river had less turbulence in its

flow where it almost became gentle.

. The gradient of the river valle had decreased as well. The valle sides had

become more o!ened where it almost had a gentle a!!earance.

York

This area can be considered the lower course of the river due to several factors. These

factors include:

#. The size of the materials of the bed load. The size of the bed load materials had

decreased and averaged the smallest of the three locations. These sizes are the

general size of materials in the lower course of a t!ical river.

). The width and de!th of the river channel. The width of the river channel had

become broad and the de!th had become dee!.

@. The flow of the river. The flow the river at this !oint had become gentle and little

or no turbulent flow was !resent. The flow can be considered to be calm.

. The gradient of the river sides. The valle sides had o!en u! ma3ing the land

become flat. The valle sides of a t!ical river become flat in the lower course of

the river0



Cross sectional area

The cross sectional area of a river is the !roduct of the average de!th and width of the

river channel. The table below shows the changes in the de!th and width of the river

channel.

Location Average depthc!" Average widthc!" Cross sectional

areac!#"

Cedar valle #$ #@.) )$@.)

Newmon3 land 9; #;. #0@%)

5anvers !en ;$ )$.) #/0

&or3 #)$$ );.9 @0$



Velocity

The velocit of a river can be considered to be the flow of water over a s!ecific distance

!er unit average time. The table below shows the changes in velocit of the river along its

course.

Location Velocity c!s$%"

Cedar 1alle %@

New 2on3land 9#

5anvers 6en #)$

&or3 #@

D&'C(AR)*

The discharge of a river is the flow of water as it !asses a !articular !oint within the river

channel along its course. This can be calculated b multi!ling the cross sectional area of

that !oint in the river with its average velocit. The table below shows the change in

discharge of the river as it travels downstream.



Location Discharge c!+,s"

Cedar 1alle #$9.9

New 2on3land #$0 #;.

5anvers 6en )$0 @).;

&or3 0 ).)

-*DL.AD

The bed load of a river is the !articles or materials that are trans!orted along the bed of

the river. The river below shows the change in the sizes of bed load materials within the

river channel as it travels down stream.



From the data !resentation is was noticeable that several changes were evident

along the course of the river. Several factors can be held accountable for these changes in

the cross sectional area0 velocit0 discharge0 and bed load materials. These factors will be

discussed below. The table below gives a general summar of the changes within the

river channel.

4ocation Cross sectional

area +cm),

1elocit +ms<#, 5ischarge

+cm@s,

8ed load size

Cedar 1alle )$@.)

New 2on3land #0@%)

5anvers 6en #/0

&or3 @0$

Cross 'ectional Area



Several factors can be held accountable for the change in the cross sectional area of

the river channel. The main factor has been erosion from the flowing water. From the

data it was seen where the velocit had increase down stream. This increase in velocit

led to an increase the rate of erosion. 'rosion is what causes both the width and the de!th

of the river valle to increase b cutting awa the sides of the ban3s of the river along

with its bed causing an increase in the size of both thus increasing the cross sectional area

of the river channel. ther factors can be held accountable for this increase. Such factors

include the material that are trans!orted also causes some amount of erosion. 8 this the

materials bounce along the bed and ban3 of the river channel when been trans!orted0

overtime this causes these surface areas to ware awa increasing the width and the de!th.

Documents

An Investigation of How Discharge Influences the Amount and Size of the Bed Load of the Negro River