As per the DEM (Sanders, 2007 and Prasad et al, 2016), the water flow direction in drainage/streams orders (Fig.6) are derived and then the watersheds are derived. These watersheds are again classified into sub-watersheds. Out of these all catchments only large catchments are selected for high rainfall runoff, the balance catchments are neglected due to less area of rainfall runoff from those areas. The area distribution of derived watershed & sub-watersheds are shown in Fig.7 & 8 and the area of the controlling catchments are tabulated in Table-1.
5.1. Rainfall Runoff:
In present study, surface runoff from all selected catchments are estimated by average of both Lacy’s (Garg, 1976) & Rational (Rahunath, 2006; Kuichling 1889). The followings empirical relationship was used for estimation of runoff. A brief description is given below:
5.1.1. Lacey’s Formula:
This formula connects rainfall(P) with the yield (Q) by the equation (Garg, 1976):
R = Daily Runoff in cm
P = Peak rainfall in cm
f = Monsoon duration factor (Table-2) &
s = Catchment factor (Table-3)
Q = Runoff in m3
R = Daily runoff in m
A = Catchment area in m2
5.1.2. Rational Method:
It is based on a simple formula that relates runoﬀ-producing potential (Rahunath, 2006; Kuichling 1889) of the watershed, the average intensity of rainfall for a particular length of time (the time of concentration), and the watershed drainage area. The formula is
Q = Runoff in m3
C = Runoff coefficient (Table-4)
P = Peak daily rainfall in m
A = Catchment area in m2
The normal rainfall for the area is 632.7 mm (IMD, 2013). The normal annual rainy days in the Udaipur district is about 96 days, it means the daily rainfall would be 6.59 mm. The lowest (58) rainy days were observed during in 2000 and the highest (145) days in 1961 (IMD, 2013). As per characteristic features of hourly rainfall in India (N.R. Deshpande et al., 2012), the peak intensity of daily rainfall event for the studied area is varies between 40-50 cm. Considering 25 % safety factor of average peak rainfall of 45 cm would be 56.25 cm. The average rainfall runoff generated from all catchments are tabulated in Table-5 at different rainfall events (Norbiato, 2009; Sepaskhan & Fard, 2010; and Zakai, 2006).
5.2. Highest Flood Level:
During rainfall event, flood point is the level at which a build of water surface has increased to a satisfactory level to cause sufficient inundation of areas that are not generally covered by water, causing an inopportuneness or a hazard to life and property. When a body of water rises to this level, it is measured a flood occurrence. The level of flood occurrence is said to be as highest flood level. Generally, in excess/peak rainfall events there is more chances of occurrence of floods. The relation between Runoff generated at peak daily rainfall water in a particular area and total area of the stream/river/pond is the highest flood level. The highest flood level of selected catchments is tabulated in Table-6.
5.3. The design criteria of Artificial Recharge System:
The design criteria of proposed artificial recharge systems are designed at peak daily rainfall event. Because at peak daily rainfall, the maximum runoff will be occurred in a single storm/intensity of rainfall, in that cause may flood will occur. Hence, the proposed system is designed at peak daily rainfall event. Here we are proposing artificial recharge system (Chiew et al, 1992; Osterkamp et al, 1995; Bredenkamp et al, 1995; Finch, 1998; Amitha, 2000; Xianfeng Sun, 2005 & Jain, 2008) like check dam/anicuts are feasible because for implementation of these systems are economically very low in cost (B.H. Ramathilagam et al., 2017). The purpose of this system is arresting the rainfall runoff and allowing to store as well as allowing the rainfall water to the ground water regime and then excess water will go through overflow provision to another artificial recharge system at a certain distance. It means the all systems are formed in step by step formation in river/stream.
The height of anicut would be as flood level develop in the catchment at peak daily rainfall but as per the Water Resources Department of the Rajasthan state has already issued directions not to allow implement of anicuts more than 2 m height (WRD, 2012). Hence, we are considering the height of the anicut is 2 m with foundation depth must be at least half of effective height. It means, the height is 2 m and as such, foundation may be kept as 1 m. The Thickness for a smaller check dams should be 1:0.3 ratio for base to spillway. The thickness of the base of check dam should be 2 times of the height. The thickness at spillway (top of check dam) will be 1/3 of the base. Therefore, the thickness of spill way would be nearly 0.7 m. Hence, Bottom thickness is 2 m & top thickness would be 0.7 m. The material used should be stone masonry/cement concrete in 1:4 mix of cement and coarse sand.
The stream density network map is shown in Fig.9 & the proposed locations of anicuts are given in Fig.10. As per the density of stream and stream orders the location of RWH structures are propose. Considering average width of the each anicut is 15 m and having average water column of 1 m and water spread area is around 40 m. Therefore, the average water holding capacity of each anicut is around 600 m3. The stored water in anicuts are very useful for irrigation, thus the pressure of ground water regime will be free during monsoon & post-monsoon period.
Based on the rainfall runoff generated at average rainfall, there would be a balance runoff after full fill of existing water bodies and storage capacity of proposed anicuts in the studied area. The data has been tabulated in Table.7. As per CGWA guidelines, the recharge potential through bed is three time of the half of the storage capacity (Table-8).
For fast recharge/to develop ground water level/ground water quality of ground water regime, we need to implement/install a couple number of percolation pits/recharge shafts. Before going to propose these systems, we need to understand the hydrogeological properties of the area. Such as, geological, geomorphological formation, depth to bed rock, type of aquifer as well as intake capacity of the water by the aquifer as determined by recharge test (CGWB, 2000).
In Udaipur district, the most of central part is occupied by the formation of Aravalli super group of Proterozoic age. Little portion of central part and western portion is also occupied by Delhi and remining portion i.e eastern is covered by Bhilwara super group of Archean age (CGWB, 2017). The formation of Geology types and sub types are given in Fig.11 & 12. The geomorphology of the area is mostly by hills (structural/linear/denudational), eastern & southern as well as in central portion in the form of pockets the Denudational origins and very small pockets of Fluvial origins are occupied (CGWB, 2017). The distribution of types and sub types of geomorphological formations are shown in Fig.13 & 14.
In the studied area, the availability of ground water is mainly controlled by the topographic and structureal features present in the geological formations. Mainly ground water occures in under unconfined to semi-confined condition in the saturated portion of the rock formation (CGWB, 2017). BGC (Banded Gneissic Complex), Granite, Phyllite, Quartizite and Schist are main aquifers in the studied area (Fig.14). The estern part is covered by BGC, central portion having Phullite and western portion is occupied by Schist, Quartzite and Granite (CGWB, 2017). The avaerage yield from BGC, Quartzite & Phyllite is 40 m3/day and Granite & Schist is 50 m3/day, taping depth is 30 m below the ground level. The depth to bed rock is shown in Fig.15. It represents that, the depth of alluvium zone from the surface level.
5.4. Recharge Test
In this test, the known volume of water was injected under gravity (slug) into the selected tube wells of different aquifers and water level measurements were carried out at the start of the test and at short intervals immediately after the known volume of water was injected into the well (CGWB, 2007). It has been found that, the recharge capacities of each aquifers are tabulated in Table-8 and the plot between time v/s drawn down cure for all aquifer are shown in Fig.16. The total recharge potential through injection system is tabulated in Table-9.
In the above proposed RWH structure (Ravi Shankar and Mohan, 2005; De Winnaar et al, 2007; Mbilinyi et al, 2007; Ghayoumian et al, 2007), the dimensional parameter of percolation pit is kept as 1 m (length) x 1 m (width) x 2 m (depth) with 8” dia. injection well of 30 m depth having 8” plain pipe up to 6 m depth Thereafter, 7” dia. necked borehole in rock may be made up to 10 m depth by DTH drilling machine. Each structure capable of recharging 42.4 m3/day by each pit. The inlet of the structure may be kept 1 m above anicut bed leaving, 1 m water column for settlement of silt/dust etc. The annual cleaning/ removal of silt/ dust from the pond bed is suggested before monsoon for efficient working of system. The schematic design of percolation pit in the RWH pond is shown in Fig.17 and the relation to the anicuts and depth to bed rock is given in Fig.18.
5.5. Impact on Ground Water Regime:
It doesn’t allow adverse impact on ground water regime of the area. It helps in controlling declining trends of water level and it helps in maintaining existing water quality of ground water and prevent from deterioration.