Water Resource model

1. Ground Water : Mod Flow Model

2. Introduction: Mod Flow Model
Today, depletion of water from aquifers that are the second largest source of
freshwater in the world, has created a serious challenge for most countries. On the
other hand, technology development has caused rapid increase in water use, with a
decline in the water table level. This requires serious, scientific management of
groundwater resources
Management of groundwater resources requires accurate understanding of aquifer
performance under current conditions, and predicting the impacts of recharge and
discharge
One of the mathematical models that simulate aquifer behavior is the MODFLOW
model. MODFLOW is a three-dimensional model that simulates flow in non -
homogeneous, non – isotropic saturated and unsteady porous environments

3. The U.S. Geological Survey (USGS) develops and supports the MODFLOW computer
program for simulation of three-dimensional, steady-state and transient groundwater flow
The standard MODFLOW releases are all based on a rectangular finite-difference grid.
There are two notable restrictions with a standard finite-difference grid.
The first is that irregularly shaped domain boundaries cannot be easily fitted with a
rectangular grid. Although there are options for inactivating parts of the grid outside the
domain of interest, the domain is still bounded by rectangular grid cells that may not
follow irregular boundaries; as a result, information about the entire grid, including
inactive cells, is read and processed
The second limitation of a rectangular finite-difference grid is that it is difficult to refine
the grid resolution in areas of interest. Column and row widths can be variably spaced in
order to focus grid resolution, but the added resolution must be carried out to the edges of
the grid.

4. Simulations of groundwater flow and transport often need highly refined
grids in local areas of interest to improve simulation accuracy. For example,
refined grids
may be needed in
•regions where hydraulic gradients change substantially over short
distances, as would be common near pumping or injecting wells, rivers,
drains, and focused recharge;
•regions of site-scale contamination within a regional aquifer where
simulations of plume movement are of interest; and,
•regions requiring detailed representation of heterogeneity, as may be
required to simulate faults, lithologic displacements caused by faulting,
fractures, thin lenses, pinch outs of geologic units, and so on.

6. 1 increase flexibility in grid design
- Add resolution where needed
- Handle pinched layers and fault offsets
2 Better solution of tightly coupled
hydrologic processes
3 Retain MODFLOW concepts and general
finite-difference approach
Why MODFLOW

7. 1.MODFLOW with Un- Structured Grids
- Three-dimensional confined/unconfined subsurface flow
- Variety of boundary conditions representing surface features
- Flow through conduit and fracture networks
- Fully implicit coupling; Raphson linearization
- Framework for implementing other domains and processes
2.Control Volume Finite Difference formulation
What is Modflow

9. Control Volume Finite Difference formulation
m1
m2
m3
m4
m5
m6
n
- Is a generalization of the finite-difference approach

11. Structured or Unstructured Grid Options

13. One of the main benefits of
MODFLOW-USG is that it is
capable of achieving a high
level of accuracy, with much
fewer grid cells than what
would be needed with
MODFLOW
Watershed boundary and boundary conditions in the conceptual model

14. Visual MODFLOW Flex
property zones in the
conceptual model
cross-sectional slice through
the unstructured grid, colored
by property zone ID

15. Twonumericalmodelswerecreatedfrom
theconceptualmodel.Bothnumerical
modelshadthesamelevelofgrid
refinementaroundthewellsandrivers
The first was a uniform finite difference grid for MODFLOW-2005,
consisiting of 50 meter cell spacing and 6 deformed vertical layers.
The result was a grid with 290 rows and 306 columns,
approximately 346,000 active cells. Since the model structure
included two layers that pinchout, a minimum thickness of 0.01 m
was enforced.
The second numerical model was an unstructured grid for
MODFLOW-USG. The Voronoi Cells honored a 50 meter cell
refinement around the rivers and pumping wells. The cells in the
discontinuous regions have zero thickness and are assigned as
inactive. The result was a grid with approximately 31,000 active
cells.

16. Advanced versions of MODFLOW that use new
formulations include:
•MODFLOW-NWT: a standalone program for
solving problems involving drying and
rewetting nonlinearities of the unconfined
groundwater-flow equation
•MODFLOW-USG: an unstructured grid
version of MODFLOW for simulating
groundwater flow and tightly coupled processes
using a control volume finite-difference
formulation
•MODFLOW-LGR: a 3D finite-difference
groundwater model with local grid refinement
The following is a list of specialized
MODFLOW variants:
•GSFLOW: a coupled groundwater and
surface-water flow model based on the
USGS Precipitation-Runoff Modeling
System (PRMS) and MODFLOW-2005
•GWM: a 3D groundwater-flow simulator
with Groundwater Management capability
using optimization
•SEAWAT: a computer program for
simulation of 3D variable-density
groundwater-flow and transport
•CFP: a model for simulating turbulent
groundwater-flow conditions
•FMP: a program for simulating dynamically
integrated supply-and-demand components

17. Cass study

18. Introduction
Groundwater is one of the most important sources of the needed fresh water for human beings
that form the largest supply of the Earth’s fresh water after the glaciers and ice caps.
Unfortunately, the groundwater resources have not been managed scientifically. As a result,
decrease of groundwater level throughout Iran due to much extraction of water and digging
wells without license is a hurdle that the public agrees on.
In order to investigate the effect of land use on the discharge and recharge of groundwater in
East China, Paul (2006) combined MODFLOW and WETPASS models with each other. The
results of the research indicated that the main reason for recharge reduction in the studied
area was urban development and agricultural lands in general. However, the lands with forests
can be effective in maintaining and preserving aquifer and its dependent ecosystems

19. Study Area

20. Materials and Methods
In order to evaluate artificial recharge through the numerical model, first of all a
conceptual model using hydrologic and hydrogeologic data, such as hydraulic
conductivity, water level in observed wells, rate of recharge resulting from
rainfall and returned water of agricultural wells, wells discharge, boundary
conditions, distribution of geological formations, surface topography of land and
the aquifer bottom elevation was generated.
The MODFLOW 2000 code in GMS software was used for modeling the
groundwater flow in the study area After preparing the conceptual model, the
study area was discretized into 42 columns and 52 rows of central block with the
width and length of 500 m

23. Results and Discussion
Following the processes of designing and calibrating the model and
then verifying the consistency of mathematical model with natural
conditions of the aquifer, the model can be used for the aquifer
management. In this study, the constructed model was used to evaluate
the effect of artificial recharge of Abbid Sarbishe on the water level of
the aquifer.
Therefore, designing an accurate model and its calibration was the
essential step to achieve the goals of the study. Using the model, the
effect of artificial recharge will be investigated from different
viewpoints

24. The Project Effective Domain According to Piezometric
Fluctuation
A (with artificial recharge) and approach B (without artificial recharge).Approach
A: This approach belongs to dry year of 2008-2009. No artificial recharge was
implemented in the plan during this year because of drought. Approach B: This
approach is considered for implementation of artificial recharge of the project and
further, is divided to subcase approach of R1, R2, R3, R4, R5, and R6 according
to hypothetical recharge of 0.00001,
0.0001,
0.001,
0.0005,
0.001,
0.005 and 0.01 mm

25. To look into the effect of recharging floodwater at north of
Gotvand, the piezometers G3, G17, and G19 in the northerly
part of Gotvand Plain were selected and their water levels at
different recharge conditions were compared. Recharge was
applied to the model as the default at the first stress period
(September) to specify the time of maximum effect on
mentioned piezometers

26. shows the equipotential lines of water level around the artificial site and the maximum
effected (groundwater mounding) area resulting from the maximum hypothetical
recharge. By magnifying the affected area of recharge, the figure has shown how the
contour lines change as a result of maximum recharge. The results of artificial recharge
also indicate that the highest effect of the plan is on piezometer G17, and G19,
respectively

27. The rise of water level in piezometer
G17 ranges from 2 mm to 2.25 m. The
rise of water level in G19 piezometer
which is the closest piezometer to
upstream ranges from 1 mm to 1.6 m.
The maximum rise of water level in this
piezometer is observed in 60 to 90 days
after water flood spreading

29. Western parts of Abbid Sarbishe floodwater spreading
had more effect on the aquifer due to less thickness of
the unsaturated part of the aquifer. It is observed,
although piezometer G19 are located upstream of the
site, its effect on aquifer is better than other piezometers
surrounding the site
Conclusions