Welcome to lecture number forty of ahh ground

water hydrology course ahh today we will talk about this modeling and management of ground

water under this ahh the topic that we will cover in this particular lecture is ground

water surface water interaction in lecture thirty nine in we have talked about this conjunctive

subsurface modeling ahhh with surface water a for over length flow case and we have already

talked about this waddle zone flow so in this particular lecture we will talk about ahh

ground water surface water interaction so ahh let us consider one shallow aquifer shallow

aquifer and we have

ground surface and then we have one stream there so this is a direction

of flow for the stream so flow and let us say that this is our water table and ahh this

is the stage height in your stream and this is the water level and the nearby aquifer

which is again shallow aquifer or unconfined aquifer in this case there will be flow from

your ground water table towards the stream and the aquifer will contribute some amount

of water in stream so again we have unsaturated zone here and this is basically ahh top cover

so grass cover or any other kind of cover is there on both the sides so this is a situation

where or aquifer is contributing in the stream so we can say that this is basically gaining

stream that means stream is gaining from our aquifer now if we see the water table contour

for this particular aquifer then ahh it will be ahh some kind of interesting thing because

there will be deviation of water table contour if there is a ahh stream in between ahhh a

particular aquifer region so let us say that this is my old domain now I have contour of

different ahh hydraulic head level so let us say this is level seventy sixty this is

fifty now ahh we have this stream here which is starting from this point now if you have

that contour near to this stream there will be some deviation so this is ahh corresponding to thirty this

is corresponding to twenty then now if we draw one obituary line here so we will see

that in aquifer ahh region your ahh ground water table is not deviating this is ahh groundwater

flow line which will be perpendicular to this so this is basically ground water flow

line and these are water table contours so in this case let us say we have two points

a and b so starting from a ahh if we move towards this stream then we will find that

there is variation and this contour is pointing towards the upstream direction so ahh in line

cross section the water table is at lower elevation ahh at the interest section point

and in this case we can say that our ground water contours will point upstream

in a gaining stream similarly if we see thr thing for loosing

stream where things are similar but only difference is

the water level in our aquifer and

stream so this is our ground surface now this is the water level and water table in the

aquifer is lower than the aquifer ahh level of water in the stream so this is our water

table so there will be movement of water from stream

towards the aquifer so we can say that this is our losing stream

like gaining stream if we draw the contour levels we will see the opposite thing compared

to our ahhh gaining stream so let us say this is our stream direction then this is our contour

level so we have this hundred ninety eighty seventy

ahh water table contours so in this case if we draw straight line as

we have drawn in for gaining stream we will find that this contour will ahh point towards

the downstream direction and that is at the intersection point with the stream so we can

say that in this case our groundwater flow is like this which is away from our stream

flow direction this is groundwater flow line so in this case we can say that if the contour

point downstream the point ahh the contour point downstream so ahh this is losing stream

so difference between losing and gaining stream is that the groundwater flow line in case

of our gaining stream because towards the stream but in case of our ahh this losing

stream this is away from the stream so another special case ahh of losing stream may be there

ahh which is ahh some kind of extreme situation for the

stream aquifer interaction so in this case this is the flow direction

and we have again that shallow water aquifer and water table is below ahh the bed level

of the stream so in this case water table is below so there will be contribution of

flow from our stream and this kind of situation will be there due to excessive pumping in

ahh aquifer region so this is basically disconnected stream

so in disconnected streams we have groundwater table ahh which is below the ahh stream this

is our stream and this is our stream bed level so this is always below the stream bed level

so these are called as disconnected streams now we need to see of what kind of fluid dynamics

is there near to stream and that is in our aquifer part

so in this one if we draw one obituary ahh cross section cross section so in this one we can divide

this whole region this is near to stream this is pointing towards stream and this is towards

our land now if we divide this the whole thing into three regions that is a b c so in this

region the behavior of the ahh total head is different

let us first draw the water table for this cross section so near to this land

there will be sharp change in the contours let us say this is one twenty this is one

ten and this is near to that sixty again some seventy eighty this is ninety then hundred

so in this region there is vertical flow almost vertical flow in this part of the ahh cross

section this is zone c or we can say this as zone so next part there will be almost

vertical contours so these are forty thirty and fron there let us say again there is change

in the pattern and now this region a things are not that vertical there is again curve

kind of contours which will be available so in region b there will be horizontal movement

of water and in this region there will be movement of water in upward direction now

if we install picometers in this three different regions then we will see what is the difference

in hydraulic head that will absorb so let us say that we are installing picometers heads

here then it will correspond to water level here

then if you are installing picometers here so it will exactly level ahh with the water

table and if we further go down then there will be again lowering of the picometric level

so lets say this is our region c prime so with zone c this c prime is nested monitoring

locations and in this nested monitoring locations we can see that for a monitoring will in this

region there will be ahh equivalent water surface which will correspond to this level

again for monitoring will ahh in this region there will be equivalent water surface which

will be corresponding to this level and this is at the top surface so this will correspond

to ahh our ahh original water level but interesting part is that almost ahh in two cases we have

found that for a particular region or picometric head is lower than the water table and the

location in this case if we try to draw the thing then we will see that this is almost

static even if we go down there will not be that much change in the water ahh level in

the picometers so this is almost same because vertically no variation in contours in this

region that is region a so this thing we can denote it as b prime now in c prime region

or else we can denote it when picometers with the straight thing

so in this region a let us say that we have one nested network of a prime so if we install

picometers here what will observe observation is that our water surface our picometric head

will be above water table so we can say that there will be ahh in first

case this is ahh lower than our water table this is almost similar to water table ther

is not much deviation but in this case it is higher so if we can install picometers

here so there will be spontaneous water flow from these picometers and if we have deep

viols in demographic depressions ahh particularly in river valleys then ahh the water is spontaneously

come out and that is ahh which is known as parting chambers when water is discharged

naturally to the surface and discharge point is called as springs so artesian wells if

we install wells and water comes out spontaneously then we say that these are artesian wells

if water comes out naturally ahh to the surface then we say that these are spring another

most important ahh point that is bank storage what is the effect of ahh bank storage on

groundwater surface water interaction bank storage effect so if we draw it you will see

that ahh with our shallow groundwater aquifer these are our ground surface in this case water level which is

this and interestingly this is our water table

during base flow so points a and b are there so what is this

bank storage we have flow direction and we have high stage here

bank storage occurs when the water level elevation in a surface water body increase

beyond the groundwater elevation in the adjacent banks so ahh we have flow direction then we

have high stage so there will be movement of water in this direction through banks there

will be movement of water towards the aquifer so this is called as ahh ahh bank storage

this is water table at high stage interestingly ahh there will be movement of

water from bank ahh from stream towards this bank and there will be elevation of water

table and ahh after some time when it reaches ahh when the balance equilibrium reaches in

the system there will be ahh higher water table near to stream compared to this lower

ahh groundwater table ahhh during base flow and in that equilibrium condition ahh still

beyond this point a and b there will be movement of water from ahh these ahh beyond these two

points in the this direction this is very complex in nature and water near the stream

in that case water near the stream ahh in that case water near the stream ahh moves

towards the stream but ahh it is beyond this a and b points which are intersection points

during high stage ahh levels and streams there will be movement of water towards the aquifer

so these are the direction of water flow situation so if you want to model this thing in ahh

practical situation then we need to idealize this particular system with some ahh simplified

ahh assumptions now let us say that we have some aquifer and in that one we have some

rectangular ahh stream channel so in that rectangular stream channel let us say this is groundwater level and here

is one region near to this channel that is river weight sediment on both the sides

and let us say this is or water level so with respect to out datum which is below this system

let us say this is our x coordinate system this is y coordinate system and this is in

the direction of that stream this is l and the saturated thickness

in this one is taken as m ahh h m and water table from pre defined datum is h and z zero

this is elevation of the stream bed level from ahh the datum and this is width of the

channel b and this is height of water in the channel and we have thickness del z prime

ahh is the thickness of bottom sediment allowing the weighted perimeter of the channel so with

this configuration ahh we can write our governing equation for ahh stream flow we can write

the equation as z del v by del l plus v del z by del l plus del z by del t equals to q

l and q v divided by b so here q v is the flow into the channel per unit width per unit

length through its weighted perimeter and q l is the lateral in flow per unit length

over the channel banks ahh and from tributaries and again ahh we need to have the momentum

equation so this s not is the bed slope and sf is the

friction slope so this is for stream flow no we need to write the equation for groundwater

flow so groundwater in unconfined aquifer ahh will have different thing in that one

dot t del h equals to s del h by del t plus qv b plus two z which is weighted perimeter

ahh of the channel now ahh this is ahh valid for the lower part of the channel and governing

equation for the other part that will be k which is hydrolic conductivity this is h m

this is saturated thickness of the aquifer h m then del h this is s y or specific ail

in this case this is ahh storage coefficient and this is specific ail for the aquifer and

there will be coupling between this ahh equation this equation this one and this one that is

continuing momentum for ahh saturated ahh confining portion and unconfined portion ahh

that will be coupled by darreys law and this is qv b two z this is torsion flex

q vis the flow into the ahh channel per unit length through its weighted perimeter so we

can say that this is the torsion flex and torsion flex ahh left hand side ahh torsion

flex right hand side we should have hydraulic conductivity and ahh this is hydraulic radiant

what is hydraulic radiant here z plus z not this is the total ahh head for stream and

we have head here that is age for any arbitrary location then we have this del z prime that

is the ahh difference between these two so we can say that this is our hydraulic radiant

and it is a coupling our all the equation then to solve it we need certain boundary

condition for open channel flow or river flow or stream flow we can either specify stage

or discharge at upstream location and we need to specify stage discharge relationship for

downstream location so this is for stream ahh thing and for aquifers

we will consider the whole region as impermeable so we have stream here which is flowing like

this and this parts this is our x and this is our y axis so this is basically del h by

del y this is zero and this case this is del h by del x is zero here also we have del h

by del x equals to zero so we can choose ahh a very large region and we can put that ahh

hydraulic head change to zero that way we can manage the ahh boundary conditions the

initial condition for stream flow ahh are depth and velocities so depth and velocity

that should be ahh known for initial condition and ahh with this configuration we can get

the variation so variation will be like this where this is our upstream direction

and this is our downstream portion so for any flood wave ahh there will be change

in the ahh hydraulic head in the aquifer with the change in the ahh fix ahh of flood wave

so if we draw one ahh simple figure maybe for some intermediate point here then we will

see that if this is our hydraulic head then for flood hydrograph with no leakage

this is positive direction this is negative and this is change in stream discharge

from steady state flow condition so this is flood hydrograph ahh this is without or no

leakage so there will be change in the ahh change in this lets consider this is with

no leakage so it will merge here and with leakage

there will be reduction this green line nd if we consider the effect of leakage then

we will see this difference ahh will plotted in this

so this will be the same so this is basically the effect of leakage

so the net effect of ahh leakage or net effect of bank storage this is bank storage or we

can say that effect of leakage leakage is or bank storage now we can have

ahh other situations where our pumping ahh will influence pumping will influence the whole thing so

let us say that we have region now this is our ground surface

and this is our water table ahhh which is matching here this is ahh confined bed water table so there

will be flow from this direction towards the stream this is actually our stream and this

is ground surface or land surface so there will be movement towards this stream now if

place some well here interestingly with small amount of pumping

there will water divivde and again there will be movement this side also this side but it

will be in normal direction but if we have some amount of heavy pumping

then it will be directly connected with the it will be directly connected with the stream

ahh stage and we will see a different ahh water ahh drow down in the pumping well this

is pumping so these are the effects ahh of aquifer on the stream and there is reverse

effect of stream on aquifer so amount of pumping also dictates the water divides so in ahh

the second case where we can have some amount of water divide for low pumping valve but

for high pumping valve this will be directly connected with the stream level so this aspect

is important because our aquifers can directly influence the stream water level so there

is always interaction between ahh streams and aquifers most importantly if we have two

reservoirs let us say that one reservoir is leaving water at certain rate another reservoir

is leaving ahhh at at different rate so in between if there is too much extraction so

in stream there will not be much water available so this is a total effect of stream water

ahh aquifer interaction ahh this ends ahh this lecture number forty