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IS 11521:1985 is the Indian Standard (BIS) for criteria for hydraulic design of check dams. This standard provides guidelines for the hydraulic design of small check dams used for soil conservation, gully control, and groundwater recharge. It covers the estimation of design flood, hydraulic design of the spillway and body wall, requirements for downstream energy dissipation, and determination of freeboard.
Lays down criteria for the hydraulic design of check dams for soil conservation and erosion control.
! This standard focuses on hydraulic design. Structural stability (overturning, sliding) and foundation analysis (seepage, piping) must be checked separately.
! Selection of the site is crucial for effectiveness and should be based on gully characteristics, catchment area, and foundation suitability.
! Inadequate spillway capacity and lack of proper energy dissipation are the most common causes of check dam failure; pay close attention to Clauses 4 and 6.
NRCS Code 410Natural Resources Conservation Service (NRCS), USDA, USA
HighCurrent
Conservation Practice Standard: Grade Stabilization Structure
Directly covers the design of structures, including check dams, to control gully erosion and stabilize channel grades.
USBR Design of Small DamsUnited States Bureau of Reclamation (USBR), USA
MediumCurrent
Design of Small Dams
Comprehensive manual for dams, with applicable hydraulic design principles for spillways and outlet works relevant to larger check dams.
FAO I&D Paper 66Food and Agriculture Organization of the United Nations (FAO)
HighCurrent
Small hydraulic structures
Provides design guidance for various small structures including weirs and checks used for water control and conservation.
NEH, Part 650, Ch. 11Natural Resources Conservation Service (NRCS), USDA, USA
MediumCurrent
National Engineering Handbook, Part 650, Engineering Field Handbook: Ponds and Reservoirs
Details design of spillways and embankments for small ponds, with principles directly transferable to check dam design.
Key Differences
≠IS 11521 specifies design flood return periods (e.g., 25-50 years) based on catchment area, whereas NRCS standards use a more rigorous risk-based approach tied to a downstream hazard classification (Low, Significant, High).
≠The Indian standard focuses primarily on masonry or concrete gravity structures with simple notch spillways. International manuals like those from NRCS or USBR provide a wider array of options, including earth embankments, pipe spillways, and complex engineered stilling basins.
≠IS 11521 may refer to local or dated empirical formulae for runoff estimation. Modern international practice, like the NRCS methods (e.g., TR-55), relies on more widely-validated, physically-based models for rainfall-runoff analysis.
≠International standards often provide more detailed guidance on geotechnical investigations and foundation treatment compared to the more generalized recommendations in IS 11521.
Key Similarities
≈Both IS 11521 and international standards utilize fundamental weir equations (e.g., Q = C * L * H^(3/2)) for calculating the discharge capacity of the spillway.
≈Core stability analyses, including checking factors of safety against overturning, sliding, and foundation bearing pressure, are fundamental requirements in both Indian and international design practices.
≈All standards recognize the necessity for energy dissipation structures (e.g., stilling basins, riprap aprons) downstream of the spillway to prevent scour and undermining of the foundation.
≈The basic criteria for site selection, focusing on narrow gorges, stable banks, and suitable foundation conditions, are common across all standards.
Parameter Comparison
Parameter
IS Value
International
Source
Design Flood Return Period (Permanent Structure)
25 to 50 years, depending on catchment size and importance.
Varies by hazard class; typically 25-year to 100-year storm event.
NRCS Code 410
Spillway Discharge Formula
Recommends Francis or Bazin formula for sharp-crested weirs; Q = 1.71 * L * H^(3/2) for broad-crested weirs.
Standard weir equation Q = C * L * H^(3/2) with C derived from experimental charts based on weir geometry.
USBR Design of Small Dams
Minimum Freeboard (above max water level)
0.3 m for small catchments (< 250 ha), 0.6 m for larger catchments.
Minimum of 1.0 ft (0.3 m) above design high water; often increased to 2.0 ft (0.6 m) for settlement and frost considerations.
NRCS Engineering Field Handbook, Ch. 11
Factor of Safety (Sliding)
≥ 1.5
≥ 1.5 for static loads; may be higher depending on load case and hazard classification.
USBR Design of Small Dams
Factor of Safety (Overturning)
≥ 1.5
≥ 1.5 to 2.0, with resultant force required to be within the middle third of the base.
USBR Design of Small Dams
Energy Dissipation Type
Recommends hydraulic jump stilling basins (e.g., IS 4997) or stone/boulder aprons.
Selection based on Froude Number; includes riprap aprons, impact blocks, and formal stilling basins (e.g., USBR Type II, III, IV).
USBR Design of Small Dams
⚠ Verify details from original standards before use
Key Values4
Quick Reference Values
Typical Design Flood Return Period10 to 25 years
Minimum Freeboard over Max Water Level0.3 m
Discharge Coefficient (Cd) for Masonry/Concrete Weir (Metric)1.7
Maximum Height generally considered< 3.0 m
Key Formulas
Q = C * L * H^(3/2) — Discharge over a broad-crested weir (spillway)