Posts

Showing posts with the label Land Subsidence

Hydraulic Structures: Siphon Spillway Mechanics and Priming Dynamics

 A Siphon Spillway is a closed conduit bent over a dam crest that uses atmospheric pressure differentials to discharge high flows under low operating heads. Flow transitions through three distinct operational phases: ​Weir Flow: Initial rising water level overflows the lower lip as a simple weir. ​Priming Phase: Flow seals the downstream leg outlet, entraining and evacuating internal air to form a partial vacuum within the siphon crown. ​Full Siphonic Flow: Continuous liquid column flow established under total differential head (H). ​The ultimate siphonic discharge (Q) is evaluated using pipe flow hydraulics: $Q = C_d \cdot A \cdot \sqrt{2 \cdot g \cdot H}$ ​Where $C_d$ is discharge coefficient $(\approx 0.6\text{ to }0.8)$ and $A$ is throat cross-sectional area. The maximum operating suction head at the crown is limited by water vapor pressure to prevent air pocket formation and cavitation. ​Siphon spillways installed on medium storage dams across India provide rapid automatic dis...
Post a Comment
Read more

Hydrogeology: Land Subsidence and Aquifer Compaction Mechanics

 Uncontrolled groundwater extraction reduces pore-water pressure, transferring hydraulic head loss into increased effective stress within fine-grained aquitard layers. According to Terzaghi’s Effective Stress Principle: $\sigma' = \sigma - u$ ​Where $\sigma'$ is effective stress, $\sigma$ is total overburden stress, and $u$ is pore-water pressure. The primary consolidation settlement $(\Delta b)$ of an aquitard layer of initial thickness $b_0$ due to head drop $(\Delta h)$ is expressed as: $\Delta b = b_0 \cdot S_{sk} \cdot \Delta h$ ​Where $S_{sk}$ is the specific skeletal storage coefficient of the aquitard matrix $(S_{sk} = \alpha \cdot \gamma_w,$ with $\alpha$ representing skeletal compressibility). When pore pressure drops below historical minimums (pre-consolidation stress), non-recoverable inelastic compaction occurs. ​Intensive groundwater extraction in urbanizing agricultural zones across Northern and Western India has raised concerns over land subsidence and damage to...
Post a Comment
Read more