OPTIMIZATION OF RAINWATER HARVESTING STORAGE STRUCTURE BASED ON HYDROLOGICAL MODELING
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Date
2012
Authors
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Publisher
Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra.
Abstract
"The practice of rainwater harvesting is quite common in the Sub·
montane zone of Maharashtra, but not much work has been reported on its
optimal design. At present the rainwater harvesting structure or ponds are
designed on thumb rule or some empirical relationships: resulting in either
large or small pond size than required. Present study therefore deals with
developing step-by-step methodology for optimizing the size of rainwater
,;
harvesting storage (RWHS) structure and formulating optimal cropping plan
for small agricultural watershed under Sub-montane zone of Maharashtra.
The purpose was to make effective utilization of limited rainwater harvested in
the pond, manage both land , water resources optimally on watershed basis,
and maximize the net benefit thereof. The small agricultural watershed (12.1
ha) at Zonal Agricultural Research Station, Kolhapur (M.S.) was the
experimental site for the present study. The water harvesting potential of
study watershed was estimated through event based and continuous
modeling using HEC-HMS model Event based simulation was carried out on
shorter time step of 5-min, whereas continuous modeling on 1-hr time step.
Two model parameters viz. initial abstraction (la:=22. 70 mm) and recession
constant (k=0.766) for event based HEC-HMS model were calibrated and
validated using 48 observed rainfall-runoff events during year 1991-2008. for
event modeling, Six parameters viz. canopy capacity (1.02 mm): surface
capacity (0.69 mm); percolation rates of soil and upper GW layers (1 .09
mm/hr for both) and storage capacity (20 .18 mm) and storage coefficient
(0.46 hr) of upper GW layer for continuous modeling were calibrated and
validated using observed rainfall-runoff data (1991-2008 except year 1997
and 2002). The active storage capacity of RWHS structure was optimized
using linear programming (LP) model in deterministic mode i.e. for known
values of daily inflow from hourly-simulated runoff and daily crop-water
demand. The optimal size RWHS was decided based on Implicit Stochastic
Optimization (ISO) concept in view of uncertainty involved in daily inflow and
climatic parameters of other years. Based on optimal storage capacity and
available rainwater storage, the optimal cropping plan was formulated using
LP model for efficient utilization of lim1ted rainwater harvested and
maximization of net benefit.
Results of the study revealed that the event based and continuous
HEC-HMS model has better applicability for study watershed. The model has
given better predictive performance for event and continuous modeling for
hydrologic response of small watershed under study. lt was verified from
minimum percent errors for runoff volume and runoff peaks (PEV= -1 .38 & -
1.06 percents and PEP= -1 .71 & +4.23 percents) coupled with lower values of
root mean square errors (RMSE =0.023 and 0.040) and normalized objective
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function (NQF;0.465 and 2.13) and higher values of Nash-Sutcliffe Efficiency
(NSE ;0.825 and 0.849) during verification. The reasonably closer match of
simulated flood and streamflow hydrographs with observed ones in terms of
shape, magnitude and symmetry confirmed the better predictive performance
of model. Short computational time step of 5-min for event based model and
1-hr continuous model were found useful for simulation of reliable
flood/streamflow hydrographs and their time related parameters. The closely
spaced flood peaks to centre mass rain hyetographs in the flood /streamflow
hydrographs indicated very rapid response of study watershed to individual
rainstorms. The active storage capacity of 6030.0 cum is found optimal for the
proposed RWHS based on minimum surplus and minimum deficit. The
optimal cropping plan formulated under rainfed situation for individual year
varies with available rainwater in the RWHS and number of supplementary
irrigation (S I) requirement to the kharif crops. The crops with minimum
number of Sl got maximum land allocation under limited water availability,
whereas the crops with maximum number of Sl get minimum land allocation.
The overall optimal cropping plan for the study watershed shows maximum
land allocation (0.96 ha) to soybean crop, followed by other crops such as
groundnut (0.85 ha), paddy (0.68 ha), finger millet (0.47 ha) and maize (0.46
ha), whereas kharif vegetable crops got minimum land allocation (0.24 ha).
The net benefit accrued from the optimal cropping plan varies with available
water yield and total number of Sl requirement. It increases with increase of
available water yield , but decreases with increase of number of Sl
requirement. The optimal size of proposed RWHS bring maximum cropped
area (3.66 ha out of 7.56 ha) under supplementary irrigation, manages both
land, water resources optimally on watershed basis and results in to
maximum net benefit thereof."
Description
"Rainfed agriculture is a complex, diverse and risk prone eco-system
subject to vagaries of monsoon, water scarcity, land degradation and poor
infrastructure. It is practiced on about 70 percent of total cultivated land (180.5
million ha). spreading over 177 districts in the country. It contributes 45
percent of total food grain production and plays a key role 1n economic
development (World Bank, 2005) and poverty reduction (lrz and Roe, 2000)."
Keywords
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Citation
CHUNALE GAJANAN LAXMAN(2012) OPTIMIZATION OF RAINWATER HARVESTING STORAGE STRUCTURE BASED ON HYDROLOGICAL MODELING, DEPARTMENT OF SOIL AND WATER CONSERVATION ENGINEERING, POST GRADUATE INSTITUTE, AKOLA, Dr. PANJABRAO DESHMUKH KRISHI VIDYAPEETH, KRISHI NAGAR PO, AKOLA, 2012, 315p