Kai Tak River – The Pulse of Kowloon EarthCache

Introduction

Welcome to the Kai Tak River (啟德河), formerly known as the Kai Tak Nullah (啟德明渠).

Originally a natural stream flowing from the hills of Lion Rock, Kowloon Peak, and Tsz Wan Shan, this waterway was straightened and encased in concrete during the mid-20th century to accommodate the expansion of Kai Tak Airport and surrounding urban development.

As a major storm drain for the East Kowloon area, the Nullah was notorious for its poor water quality and foul odor throughout the years as it often received untreated industrial waste from San Po Kong and household refuse from the squatter huts that lined its banks.

Following extensive rehabilitation efforts starting in the 1990s, the river has seen a dramatic recovery. Today, it stands as a prime example of urban river revitalization.

This EarthCache explores the river's transformation from a "dead" concrete box into a living ecosystem with the introduction of modern eco-hydrology through careful and strategic engineering.

Eco-Hydrology & Flow Engineering

In traditional urban engineering, a "nullah" is designed as a smooth, concrete box. The primary objective is to move stormwater from inland to the sea as quickly as possible to prevent flooding. However, this creates a "biological desert." The resulting high-velocity laminar flow (water moving in smooth, parallel layers) lacks the turbulence and physical diversity presented in lower-velocity turbulent flow that is required for organisms to survive.

To revitalize the Kai Tak River, the Drainage Services Department (DSD) utilized eco-hydraulics. By introducing specific physical obstacles and biological elements, they transformed a uniform drainage channel into a complex river system with high hydraulic diversity:

1. Flow Deflectors 
   
   

   To mimic the morphology of natural rivers, large boulders were strategically placed along the riverbed, and artificial "bends" were integrated into the banks. These structures act as deflectors. As water strikes these obstacles, it creates low-pressure zones immediately downstream called eddies. These eddies break up the uniform flow, oxygenate the water through turbulence, and provide varied velocities that allow fish and insects to feed, rest, and thrive.

2. Fish Shelters
   
   

   Hollowed-out stone structures and recessed "pockets" were installed along the riverbed and lower bank walls. These serve as refugia—safe havens for aquatic life. During Hong Kong’s intense summer rainstorms, water levels and velocities rise dramatically; without these shelters, most aquatic life would be swept away by the force of the current.

3. Riparian & Aquatic Vegetation
   
   

   Vegetation was introduced to the riverbanks and the riverbed to serve both ecological and structural functions. Submerged plants increase hydraulic roughness (friction), which naturally slows the water flow and helps prevent erosion. Additionally, these plants act as a biological filter, trapping suspended sediments and improving overall water quality.

Logging Tasks

To log this EarthCache, please observe the river at the posted coordinates and send your answers to the following questions via the Message Center or email.

1. Flow Deflector Observation

Locate a cluster of large rocks within the river channel.

• A. Compare the water surface immediately upstream (in front) of the rocks to the surface immediately downstream (behind). Describe the differences in movement and texture.
• B. Can you identify an eddy (water circling back or remaining still) behind the rocks?
• C. Do you see any birds or fish near these rocks? Are they hanging out in the fast-moving water or the calm spots? Explain how the deflector makes this spot a better habitat for them.

2. Fish Shelter & Biodiversity Search

Examine the base of the river walls or the sides of the artificial islands.

• A. Locate the hollowed-out Fish Shelters. Describe their shape and orientation (e.g., are the openings facing into the current or away from it?).
• B. Look closely at the openings or the rough stone surface of the shelters. Do you see any fish hiding inside? Are there any smaller organisms (like algae or snails) clinging to the stones?
• C. Why do you think fish prefer these "rough" stone walls over a smooth, flat concrete wall?

3. The Engineered Riverbank

Observe the green planters sitting on the ledge between the walkway and the water. This is a "flood buffer zone" designed by engineers.

• A. Estimate the height from the surface of the water to the top of that planters edge. Why do you think the engineers chose this specific height?
• B. The plants here are specifically picked because they can survive being submerged occasionally. In your own word, how do you think these plants will help slow down the water in case of flooding?

Optional Photo

Post a photo of yourself, your GPS, or a personal item along the Kai Tak River Trail to document your visit. Please ensure your photo does not reveal the answers to the tasks above.

Sources:

• Kai Tak River – Profile of Kai Tak Nullah. (2011, March). Kai Tak River (ktd.gov.hk). The Government of the Hong Kong Special Administrative Region, Drainage Services Department. Retrieved December 2025, from https://www.ktd.gov.hk/kaitakriver/eng/existingkaitaknullah.html

• DSD ECO – River Channels/Overview. (2022, February). DSD ECO – River Channels/Overview. Drainage Services Department (Hong Kong). Retrieved December 2025, from https://www.dsd.gov.hk/EcoDMS/EN/River_Channels/Kai_Tak_River/Overview.html

• Kai Tak River Improvement Works. (2021, December). Drainage Services Department. Retrieved December 2025, from https://www.dsd.gov.hk/EN/HTML/20534.html

• Drainage Services Department – Newsletter No. 7 (Kai Tak River – Wong Tai Sin Section). (2017, August). Drainage Services Department. Retrieved December 2025, from https://www.dsd.gov.hk/others/KTR/en/issue7.html

• Drainage Services Department – Newsletter No. 9 (Kai Tak River – Wong Tai Sin Section). (2018, May). Drainage Services Department. Retrieved December 2025, from https://www.dsd.gov.hk/others/KTR/en/issue9.html