CIVIL ENGINEERING, HYDROLOGY, HYDRAULICS, SCIENCE, CYCLE, please break each sect
ID: 1710739 • Letter: C
Question
CIVIL ENGINEERING, HYDROLOGY, HYDRAULICS, SCIENCE, CYCLE, please break each section down into steps on how to get the answer!!!!!! PLEASE NEED IT ASAP!!!!!
Question 1 (a) What changes do you see occurring in meteorological and collection methods over the next 20 years? meteorological and hydrological data (b) Describe briefly the principles of the Tipping Bucket an d the Current Meter approaches in hydro-meteorological data collection e terms "calibration", "validation" and "prediction "use types "used in for a (c) Define the ter hydrological modelling and list possible input and output data hydrological model (d) Illustrate (draw and name) three possible loss models that can be used in hydrological modelling e) Describe three possible methods in computing average rainfall of a ca tchment sitives and negatives of each method. Question 1-i) The bottom width of the ABC rectangular channel shown in Figure 1 is 5m. The Manning's roughness throughout the channel can be taken as 0015 slopes of the AB and BC are 1 in 1000 and 1 in 200 respectively. Flow at upstream of A is uniform while tail water level (where ABC delivers water to the crossing channel (at C) running perpendicular to ABC) is 3m. Uniform flow depth of the AB channel is also 3m. The flow depth at the vena contractor downstream of the gate is 500mm. The velocity at the upstream of the gate and energy losses at the gate can be considered as negligible. second conjugate depth of any hy The draulic jump formed in a mild slope, as well as the first conjugate depth of any hydraulic jump formed in a st betaken as the uniform fow depth of the respective channel. eep slope, canExplanation / Answer
Due to climate change, cities need to adapt to
changing rainfall and rainwater run-off dynamics. In order
to develop an corresponding process based run-off model for
pavements, we had to improve the measurement technique to
detect run-off dynamics in an appropriate high resolution.
Traditional tipping buckets (TB) have a comparable low
volume resolution, capable to quantify the highest intensities
in a range of expected flows. This results in varying temporal
resolutions for varying flow intensities, especially in
low resolutions for small flow events. Therefore, their applicability
for run-off measurements and other hydrological
process studies is limited, especially when the dynamics of
both small and big flow events shall be measured.
We improved a TB by coupling it to a balance and called it
weighable tipping bucket (WTB). This paper introduces the
device set up and the according data processing concept. The
improved volume and temporal resolution of the WTB are
demonstrated. A systematic uncertainty of TB measurements
compared to WTB measurements is calculated. The impact
of that increased resolution on our understanding of run-off
dynamics from paved urban soils are discussed, exemplary
for the run-off and the surface storage of a paved urban soil.
The study was conducted on a permeably paved lysimeter
situated in Berlin, Germany. Referring to the paved surface,
the TB has a resolution of 0.1 mm, while the WTB has a
resolution of 0.001 mm. The temporal resolution of the WTB
is 3 s, the TB detects individual tippings with 0.4 s between
them. Therefore, the data processing concept combines both
the benefits of the balance to measure small intensities with
that of the TB to measure high flow intensities.
During a five months period (July to November 2009) 154
rain events were detected. Accordingly, the TB and WTB
detected 47 and 121 run-off events. The total run-off was
Correspondence to: T. Nehls
(thomas.nehls@tu-berlin.de)
79.6 mm measured by the WTB which was 11 % higher than
detected by the TB. 95 % of that difference can be appointed
to water, which evaporated from the TB. To derive a surface
storage estimation, we analyzed the WTB and TB data for
rain events without run-off. According to WTB data, the surface
storage of the permeable pavement is 1.7 mm, while using
TB data leads to an overestimation of 47 % due to low
volume resolution of the TB.
Combining traditional TB with modern, fast, high resolution
digital balances offers the opportunity to upgrade existing
TB systems in order to improve their volume detection
limit and their temporal resolution, which is of great
advantage for the synchronization of water balance component
measurements and the investigation of hydrological
processes. Furthermore, we are able to quantify the uncertainty
of flow measurements gained with traditional tipping
buckets.
1 Introduction
The urban water balance and its dynamics is not understood
completely (Ragab et al., 2003). Measuring run-off from permeable
paved urban soils in a high temporal and quantitative
resolution is the prerequisite for the formulation of a processbased
run-off model. Such a model, based on meteorological
data and pavement characteristics would be capable to
predict changes in the urban run-off dynamics for changing
rain sum and intensity distribution due to climate change as
forecasted (Arnbjerg-Nielsen, 2006). Such models are therefore
of interest for the development of climate change adaptation
strategies for urban areas, such as drainage adjustment
(Arnbjerg-Nielsen and Fleischer, 2009; Faram et al., 2010),
use of run-off water for cooling by evapotranspiration (Gobel
et al., 2007b; Nakayama and Fujita, 2010) or risk assessment
for increased infiltration (Gobel et al., 2007a; Nehls et al.,
2008).
Published by Copernicus Publications on behalf of the European Geosciences Union.
1380 T. Nehls et al.: Weighable tipping bucket
1.1 Studying run-off from paved urban soils
In our study, the water balance of pavements is measured
using 1 m2 weighable lysimeters (for details see Rim et al.,
2009). On those lysimeters, small rain events lead to small
absolute run-off flows. However, these have to be detected.
For understanding the processes which influence run-off generation
from paved soil surfaces, small rain events are of the
same or even higher importance than storm events for two
reasons:
(i) Figure 1 demonstrates the long term precipitation event
sum distribution. It highlights the contribution of small
precipitation events to the cumulative sum of precipitation.
Similar, precipitation events with small intensities contribute
substantially to the total sum of precipitation. At the Station
Marienfelde 5 %, 50 % and 95 % of the cumulative rainfall
are generated by rain fall events with intensities smaller than
0.0076, 0.0263 and 0.1886 mm min1
respectively.
(ii) The run-off (RO) is a non-linear function of precipitation
sum (P) and intensity (Sen and Altunkaynak, 2006).
That means different run-off generation processes might be
of differing effectiveness for different rainfall sums and intensities.
Therefore, one needs to study run-off for small and
heavy rainfall events.
The processes to study include infiltration of rain water
into the soil through cracks and pavement joints, surface storage
due to depletions in the relief and due to porosity of pavement
materials, evaporation of rain water from the surface
and run-off concentration, e.g. surface flow dynamics. The
surface storage VS [mm] also named initial loss or rain loss
(Hino et al., 1988; Arnbjerg-Nielsen and Harremoes, 1996)
may have a great influence on run-off especially for small
rain events. A certain amount of the rain water can be stored
at the surface of the pavement and in the seam soil material
between the pavers (Nehls et al., 2006). As water can
evaporate from VS, it is important to quantify it (Mansell and
Rollet, 2009). The surface storage of pave stones can be easily
measured for different rain intensities in the laboratory.
It should additionally be estimated for whole pavements, including
the storage capacities of the surface relief and the
seam soil material. It can be estimated from the mass increase
of a paved weighable lysimeter during a rain event
until run-off starts. However, this requires a mass detection
system for the lysimeter, which has a high mass and temporal
resolution. Wind, which accompanies rain events frequently
can disturb such measurements.
Alternatively, the surface storage can be gained from runoff
measurements for rain events with differing intensities
and rain sums. Because of the great importance of small
rain events and low intensity events, the measuring device
must be capable to quantify run-off events with very differing
intensities, each with the appropriate temporal and volume
resolution. For the detection of small flow rates down
to 0.007 mm min1
a bucket on a balance with a high resolution
would be capable. However, the logger system and
0
25
50
75
100
0 5 10 15 20 25 30
precipitation event sum [mm]
cumulative precipitation [%]
long term period 1961-1994
measuring period July to November 2009
1.8
4.47
28.64
Fig. 1. Contribution of individual precipitation event sums (separated
by a 10 min dry period) to the cumulative sum of precipitation
at the station Berlin-Marienfelde, 1961–1990 (solid line,
N = 11363) and of the rain events during the observation period of
this study, 8 July to 30 November 2009 (dashed line, N = 154). The
5 %, 50 % and 95 % quantiles are marked for the period 1961–1990.
the balance must have a high mass and temporal resolution
and good shock absorption. The higher the resolution of a
balance, the smaller is its weighing range. In our case the
available balance has a range of 4000 g. An according 4 l
bucket would be filled after less than one average rain event,
assuming a run-off coefficient of 1 and the rain distribution
from Fig. 1. So the use of a bucket would lead to high maintenance
efforts, while a tipping bucket is self-emptying and
enables a continuously, low maintenance monitoring of runoff
events. Alternative flow measurement techniques such as
venturi canals, rotameters or rotary piston meters work only
with completely filled tubes or filled flow cross sections of
gutters thus would complicate the setup.
1.2 Tipping buckets in hydro-meteorological
instrumentation
The functional principle of tipping buckets (TB) is to count
how often the two buckets with known volume are filled and
self-emptied. It is known since the 1950ies and since then
often used in hydro-meteorological instrumentation such as
rain-gauges (W.M.O, 1961) or stem flow meters (White and
Rhodes, 1970). Tipping buckets have also been regularly employed
for run-off measurements since the early 1960s (Pillbury
et al., 1962; Edwards et al., 1974; Khan et al., 1997).
They are also used in wick samplers and lysimeters for the
measurement and sampling of seepage water and for multicompartment
sampling