Hjulstorm Curve By Qamra's Group

The contents: •Meaning •Interpretation of the graph. •Explanations.

The Hj ul sto rm cur ve is a graph use d b y h ydrolo gists to de te rmin e whe th er a rive r wi ll e rode , tr anspor t, or de posi t se di men t. The graph wi ll tak e sedi me nt siz e an d chann el v eloc ity into acc oun t.

The in ter pretati on of the hj ul str om’ s c ur ve /graph

 The

x-axis shows the size of the particles in millimeter (mm).  The y-axis shows the velocity of the river in cm/s.  Hjulstrom’s graph shows relationships between stream velocity and ability to transport materials of varying sizes.  There are two curves lines drawn in a Hjulstorm curve: critical erosion velocity and settling or fall velocity.

THERE A RE THREE IMPORT ANT FEA TURES OF HJU LST ROM’ S C URV E. The

smallest and largest particles requires high velocities to lift them. High velocities are required to entrainment than for transport. When velocity falls below at certain level, deposition of particles occurs.

Mean or critical erosion velocity: it is approximate velocity needed to pick up and transport, in suspension, particles of various sizes. (minimum velocity for load to be moved).

Mean fall or settling velocity: it is Velocity at which particles of a given size become too heavy to be transported and so will fall out of suspension and be deposited. (minimum velocity, needed to continue transporting load).

FROM TH E GRAPH :

sand

Sma ller parti cles of sand r eq ui re rel ati vel y low ve lo ci ti es to pi ck them

gravels

La rg er gra ve ls an d bo ulder s re qu ire hig h ve lo cit ies to sta rt mo vi ng .

boulders

cl ay

The sm all es t par ti cl es su ch a s cl ay an d sil t requi re a hi ghe r ve lo ci ty to pick t he m up . Thi s i s be caus e t he y ten d to sti ck toge th er (coh esi on) an d re si st

si lt

 Ab ov e

th e c rit ic al e rosion ve locity curve , th e zone on t he g raph is lab elle d ‘e rosion ’. This in dic ate s th e v eloc itie s at w hic h mate ria l is ac ti ve ly b ein g re mov ed b y th e ri ve r’s flow.  Th e graph also shows the th re sh old v eloc ity below w hic h d if fere nt siz ed p artic les are de posite d (shown on the gr ap h as the ‘f all ve loc ity’ curve ). A s th e ve loc ity de cre ase s, sm al le r a nd smalle r par tic le s are de posite d on th e c hannel be d.  Th e zon e be tw een the c ritic al e rosion v eloc ity curve an d th e f al l v eloc ity c urv e is lab elle d ‘ tran sport ’. This i ndic ate s th at p artic les contin ue to move ( ei th er i n susp ension or b y trac tion ) at v eloc it ie s th at are low er than th ose r equ ir ed to star t th em m ov in g.

Don e b y: Alee q Kha lizah Saufi Qa mr a

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