Geoscience Reference
In-Depth Information
upstream from the station, from a map, if the drainage density is not known. Use Equations (10.174)
to estimate effective regional values of
k
0
and
n
e
. Test the sensitivity of this result to the assumed
value of the effective regional aquifer depth
D
. (In the United States, such data records can be
found on the web at http://waterdata.usgs.gov/usa/nwis/sw).
10.13
Multiple choice. Indicate which of the following statements are correct. The partly saturated zone
above the water table during base flow, i.e. during drainage of an unconfined aquifer in the absence
of rainfall:
(a)
has a water pressure which is lower than atmospheric;
2
h
=
0
,
when the aquifer is uniform and homogeneous;
(b)
obeys Laplace's equation
∇
(c)
is
sometimes
described
approximately
by
means
of
the
hydraulic
groundwater
theory;
(d)
is most important in shallow (instead of deep) aquifers consisting of fine textured (instead
of coarse) materials;
(e)
is thicker while flow is taking place, than after the complete cessation of base flow
(assume that throughout the outflow process the water table is well below the ground
surface);
(f)
has an attenuating effect, such that the outflow from the aquifer is initially (shortly after
the cessation of storm runoff) smaller than the value calculated by neglecting the partly
saturated zone (and keeping the saturated flow parameters the same);
(g)
is subject to the principle of continuity and Darcy's law;
(h)
necessitates the consideration of hysteresis when the unconfined aquifer is initially fully
saturated.
10.14
Multiple choice. Indicate which of the following statements are correct. Unconfined aquifers:
(a)
prevent the deep seepage of water;
(b)
containing water both at pressures larger and at pressures smaller than atmospheric, usually
have a free surface, which is a sharp interface between a fully saturated and a completely
dry region;
(c)
can be an important source of base flow into rivers and lakes;
(d)
can suffer water depletion due to evapotranspiration;
(e)
always behave as linear reservoirs, whose outflow, in the absence of rain or other recharge,
is given by an exponential decay function.
10.15
Multiple choice. Indicate which of the following statements are correct. Hydraulic groundwater
theory requires that:
(a)
Darcy's law is valid only in the partly saturated zone;
(b)
the hydraulic head
h
does not vary along the impermeable layer;
(c)
the impermeable layer is horizontal;
(d)
the flow rate is proportional to the slope of the free surface;
(e)
recharge from infiltration is to be neglected;
(f)
the magnitude of the specific flux is constant (i.e. uniform) along the coordinate that is
normal to the impermeable layer.
10.16
Multiple choice. Indicate which of the following statements are correct. The Boussinesq equation
(10.30):
(a)
requires
the
assumption
that
a
practically
saturated
capillary
fringe
cannot
be
considered in the analysis;
