(a) (i) The Gross Command Area for a distributary is 15000 hectares, 80% of which can be irrigated. The intensity of irrigation…

(a)(i) Discharge at the head of the distributary

Gross command area = 15,000 ha; culturable command area = 0.8 × 15,000 = 12,000 ha.

Rabi: area irrigated = 60% of 12,000 = 7,200 ha; with a duty of 2,500 ha/cumec the discharge needed is 7,200/2,500 = 2.88 cumec.

Kharif: area irrigated = 30% of 12,000 = 3,600 ha; with a duty of 1,500 ha/cumec the discharge needed is 3,600/1,500 = 2.40 cumec.

The two seasons do not overlap, so the distributary must be designed for the larger of the two: the discharge required at its head is 2.88 cumec, governed by the Rabi crop. The annual intensity of irrigation is 90%, but it is the seasonal demand, not the annual, that fixes the channel capacity.

(a)(ii) Lacey's regime theory, and comparison with Kennedy

Lacey held that a channel in alluvium carrying a constant discharge and a constant sediment load will, if allowed to adjust its width, depth and slope, reach a stable or 'regime' condition in which it neither silts nor scours. The regime dimensions depend on the discharge Q and on a silt factor f = 1.76√mr, mr being the mean particle size in mm. His equations, for Q in cumec and lengths in metres: velocity V = (Qf²/140)^(1/6); wetted perimeter P = 4.75√Q; hydraulic radius R = 2.5V²/f; bed slope S = f^(5/3)/(3340 Q^(1/6)); and the section is taken as a semi-ellipse. Given Q and f, the section and slope follow directly without trial.

Initial regime is the state of a newly made channel that has adjusted its bed slope and depth by silting or scouring but not its width, because the banks are stiffer than the bed; it appears stable but is not in true regime. Final regime is reached when the channel has freely adjusted all three, width, depth and slope, so that the section is in equilibrium with the water and sediment it carries; Lacey's equations apply to this state. A third state, permanent regime, is a lined or rigid-boundary channel that cannot change at all.

Comparison with Kennedy. Kennedy, from observations on the Upper Bari Doab canal, gave one relation, the critical velocity V₀ = 0.55 m y^0.64 (y the depth, m the critical velocity ratio, near 1), at which the silt just stays in suspension; the section had to be found by trial with Kutter's equation, the width or B/D ratio being chosen by the designer, and the slope being assumed. Lacey provides a complete set of equations that fix width, depth and slope uniquely, so no trial and no assumed slope is needed. Kennedy related the silt-supporting eddies to the bed only and used the depth; Lacey held that eddies are generated over the whole wetted perimeter and used the hydraulic radius. Kennedy allowed for the grade of silt only through m and gave no slope equation; Lacey brought the silt grade in explicitly through f, and gave the slope. Kennedy took the trapezoidal section; Lacey the semi-ellipse. Kennedy's method allows the designer freedom in B/D, which can be useful, whereas Lacey's fixed P = 4.75√Q gives wide, shallow channels and is strictly valid only for channels in true regime carrying the same silt as the parent river. Kennedy's is a fair first approximation; Lacey's is the basis of present design.

(b) Leachate in a landfill

Leachate is the liquid that drains from a landfill: rain and moisture that has percolated through the waste, together with the water released by decomposition, carrying with it the soluble and suspended matter it has picked up. It is dark, foul-smelling, high in BOD and COD (tens of thousands of mg/l in a young landfill), ammonia, chlorides, dissolved solids, heavy metals and organic contaminants.

Left unmanaged it seeps from the base of the fill into the ground and pollutes the groundwater over a wide area for decades, making wells unusable; it runs off into streams and lakes, deoxygenating them and killing aquatic life; it accumulates in the fill, raising the water table within the waste, weakening it and making slopes unstable; it produces odour and attracts vectors; it corrodes structures; and its toxic and carcinogenic content enters the food chain. The ammonia and heavy-metal load persists long after the biodegradable fraction has gone.

In a sanitary landfill leachate is managed at four points. Prevention: the site is chosen away from aquifers, the waste is placed in cells and covered daily, and the final cover (compacted clay, geomembrane, drainage layer and topsoil, graded to shed water) keeps rain out; surface run-off from outside is diverted round the site. Containment: the base is lined with a composite liner, a compacted clay layer of low permeability (k < 10⁻⁷ cm/s) overlain by an HDPE geomembrane, often doubled with a leak-detection layer between. Collection: above the liner a drainage layer of gravel with perforated pipes laid to a slope leads the leachate to sumps, from which it is pumped out; the head of leachate over the liner is kept below 30 cm. Treatment: the collected leachate is treated on site (anaerobic followed by aerobic biological treatment, ammonia stripping, chemical precipitation of metals, membrane or activated-carbon polishing) or carried to a sewage treatment works; recirculating part of it through the fill accelerates stabilisation. Monitoring wells up-gradient and down-gradient of the site check that the system is working, and the site is managed for 20–30 years after closure.

(c) Screening, scoping and public consultation in EIA

The EIA process in India is governed by the EIA Notification of 2006 (as amended) under the Environment (Protection) Act, 1986.

Screening decides whether a project needs an EIA at all, and at what level. Purpose: to keep the effort proportionate, so that only projects likely to have significant impacts go through the full study. Procedure: the proponent submits Form 1 (and Form 1A for building projects) with a pre-feasibility report to the appraisal authority. Projects are categorised by type and size in the schedule to the notification: Category A projects (large thermal plants, major mining, big irrigation, ports, airports and so on) go to the Ministry of Environment, Forest and Climate Change and its Expert Appraisal Committee; Category B go to the State Environment Impact Assessment Authority and its State Expert Appraisal Committee, which screens them further into B1, which require an EIA, and B2, which do not. Location in a notified sensitive area can raise a project's category.

Scoping decides what the EIA must cover. Purpose: to identify, early, the impacts that matter and the alternatives to be studied, so that the study is focused and the terms of reference are known before work begins. Procedure: the EAC or SEAC, on the basis of Form 1, the pre-feasibility report and, if it wishes, a site visit, issues the Terms of Reference for the EIA within 60 days; the ToR list the baseline surveys (air, water, noise, soil, ecology, socio-economics over one season at least), the impacts to be assessed, the alternatives of site and technology to be considered, and the contents of the environment management plan. The EIA report and EMP are then prepared by an accredited consultant against those ToR.

Public consultation puts the draft EIA before the people affected. Purpose: to obtain the concerns of the local community and other stakeholders and to have them answered in the final report, so that the decision is informed and the project is accepted. Procedure: it has two parts, a public hearing at or near the site and written responses from others with an interest. The proponent submits the draft EIA to the State Pollution Control Board, which publishes a notice, makes the draft available and conducts the hearing within 45 days, chaired by the District Magistrate or a representative, with the proceedings video-recorded and the minutes signed; the SPCB forwards the proceedings to the regulatory authority. The proponent must address the material concerns raised in the final EIA and EMP, which then go to the appraisal committee. Certain projects (modernisation without increased pollution, projects within notified industrial estates, defence projects, some irrigation projects) are exempt from public consultation. Appraisal by the committee and the grant of environmental clearance with conditions, followed by post-clearance monitoring, complete the process.