Grading part 1 on Contours, Grading, and Landforms

Introduction to Water Villas

  • Features of Water Villas:

    • Include a pool.

    • Offer decks for lazy afternoons.

    • Provide spaces for social diners and banquets.

    • Feature a private marina.

    • Are designed to be private and reclusive.

    • Give the sensation of floating on water.

    • Allow for swimming on the lake.

  • Conceptual Imagery: "This is our villa on the lake… I often sail to the confluence on a beautiful afternoon."

Contour Line Basics

  • Definition: A contour line connects points of the same elevation.

  • Fundamental Rules for Contour Lines:

    • Contours always close (form a loop).

    • Contours (almost) never cross each other.

    • Contours never (really never) split.

    • A contour line doesn't 'stop' arbitrarily in the middle of a map.

    • Intervals: The vertical distance between adjacent contour lines is set and consistent.

    • Water Flow: Water always runs at a right angle (90^ ext{o}) to the contour lines, flowing from higher to lower elevations.

Contour Drawing Conventions and Slope Types

  • Drawing Conventions:

    • Dashed vs. Solid Lines: Used to distinguish between existing, proposed, or specific types of contours.

    • Index Line: A thicker, often labeled, contour line that appears at regular intervals (e.g., every fifth contour) to make reading easier.

    • Valley vs. Ridge: Specific contour patterns indicate valleys or ridges.

    • Spot Heights: Individual points labeled with their exact elevation.

    • Position of Values: Elevation values are typically placed on the uphill side of the contour line or within the contour itself.

  • Basic Slope Types:

    • Convex Slope: Gradual at the top, becoming steeper further down. In plan view, contours are closer together downhill.

    • Concave Slope: Steep at the top, becoming more gradual further down. In plan view, contours are further apart downhill.

    • Uniform Slope: Contours are evenly spaced, indicating a consistent gradient.

General Landforms

  • Concave Slope:

    • Side View (Section D): Appears steep at the crest and gradually flattens downwards.

    • Plan View: Contours spread out as elevation decreases, looking "concave down."

  • Convex Slope:

    • Side View (Section E): Appears gradual at the crest and rapidly steepens downwards.

    • Plan View: Contours converge or come closer together as elevation decreases, looking "convex down."

  • Uniform Steep Slope: Characterized by closely and evenly spaced contour lines.

  • Cliff / Steep Rock Face: Formed by converging or very tightly packed contour lines, indicating a sudden and significant change in elevation.

  • Terraced Slope: Resembles a series of steps, with relatively flat areas interspersed with steep drops.

  • Hill: A landform that extends above the surrounding terrain and often has a distinct summit. Represented by concentric closed contours where values increase towards the center.

  • Camelback or Saddle: A landform consisting of two knolls (small hills) of near-equal size situated on a ridge line, with a low-lying area or depression in between them.

  • Ridge: A chain of mountains or hills that forms a continuous elevated crest for some distance. Contour lines typically form V-shapes that point downhill, with higher elevations towards the point of the V.

  • Valley: A low-lying area, often with a river or stream running through it. Contour lines typically form V-shapes that point uphill, with lower elevations towards the point of the V.

  • 'Poort' / Gateway: An opening or pass in a ridge.

  • Neck: A low point positioned between two domes or knolls along a ridge line.

  • Mountain Spur: A projecting ridge that extends outwards from a larger mountain mass.

  • Ravine / Canyon: A deep valley bounded by steep slopes, typically with little flat land at its base. Characterized by tightly spaced and converging contours along its sides.

  • Waterfall: Indicated by contours that are stacked very closely together or coincide along a line, signifying a sharp, vertical drop in elevation.

  • Dam: A man-made structure designed to hold back water, often creating a reservoir. Its presence will significantly alter original contour patterns.

  • Watershed: An area of land where all surface water from rain, melting snow, or ice converges to a single outlet point, such as a river, lake, or ocean.

Interpolation

  • Purpose: Interpolation is used for:

    • Determining new contour lines or heights between existing, known lines or spot heights.

    • Calculating the precise spot height at a certain point located between two known contour lines.

Grading and Drainage Principles

  • Grading for Circulation (Roads):

    • Cross-sections often include cut slopes, fill slopes, paved roads, concrete walls, shoulders, and grass swales.

    • Example Dimensions/Slopes: 100 ext{mm} crown, 120 ext{mm} high curb, 200 ext{mm} deep swale.

    • Typical Slopes: 3\% along the road (1:33 or 0.0303), 2\% cross slope on a walk (1:50 or 0.02).

  • Road Cross-Section Types:

    • Horizontal: No crossfall or crown.

    • Constant Gradient to One Side: Slopes uniformly in one direction.

    • Crown: Slopes downwards symmetrically from a raised center point.

    • Center Drain (Valley Cross-section): Slopes inwards from both sides towards a central drainage channel.

    • Kerb: A raised edge, typically concrete, bordering a road or path.

  • Road Crown Grading Calculation Example:

    • Given a road width of 3.0 ext{m}, a 3\% slope, and a curb height of 0.09 ext{m}.

    • Crown height: A = (0.003) imes (3.0 ext{m}) = 0.09 ext{m} or 9 ext{cm}.

  • Drawing Proposed Contours: The process involves drawing new contours to reflect desired changes in elevation and blending them seamlessly with the existing landscape.

  • Grading for Drainage on Platforms:

    • Problem: Surface water running from the foot of a cut slope directly onto a platform.

    • Solution: Grade a drainage channel between the foot of the cut and the platform's edge.

    • Function: This channel diverts surface water to flow around the topside of the platform and out onto the natural slope, preventing pooling on the platform.

    • Drainage Channel Relationships to Platform Edge:

      • (a) Constant Length: If the horizontal distance between the channel center and the platform edge is constant, the channel's side gradient will steepen as its length increases.

      • (b) Constant Side Gradient: If the side gradient between the channel center and the platform edge is constant, the channel's centerline will progressively move further from the platform edge as its length increases.

    • Key Planning Step: The horizontal forms (plan views) of all drainage channels must be determined and plotted before calculating and drafting amended contours.

Cut and Fill Operations

  • Cut: The process of removing earth material from a site.

    • Advantages: Creates a stable base, suitable for areas too steep for filling, generally experiences less erosion.

    • Disadvantage: Requires material to be exported from the site, which can be expensive.

  • Fill: The process of adding earth material to a site.

    • Advantages: Can transform a low-lying area into a usable space.

    • Disadvantages: Requires material to be imported (expensive), the filled area is inherently less stable and requires elaborate foundations for construction, precise compaction is necessary, and fill slopes are more prone to erosion.

Slope Gradients and Standards

  • Gradient Formula: G = D/L

    • G = gradient

    • D = height difference (vertical change)

    • L = length (horizontal distance)

    • Note on Convention: In Australia, accepted usage for gradient ratios is vertical:horizontal (e.g., 1:4 for 1 unit vertical change over 4 units horizontal).

  • Percentage Slopes: A 100\% slope corresponds to a 1:1 ratio (a 45^ ext{o} angle), while a 10\% slope corresponds to a 1:10 ratio.

  • Angles of Repose (for Cut Slopes): The maximum stable angle at which a given material can stand without collapsing.

    • Solid well-bedded rock: 90^ ext{o}

    • Ordinary rock: 1:1.5 (53^ ext{o}, approximated)

    • Poor rock, sound shale, cemented gravels: 1:1 (45^ ext{o}, approximated)

    • Firm soils, compact gravel, boulders & earth: 1:1.25 (39^ ext{o}, approximated)

    • Loam, ordinary clay: 1:1.5 (33^ ext{o} 30', approximated)

    • Loose gravel, wet clay: 1:2 (26^ ext{o} 30', approximated)

    • Sand: 1:3 (18^ ext{o}, approximated)

    • Loose sand, soft clay: 1:4 (14^ ext{o}, approximated)

  • Angles of Repose (for Fill Slopes):

    • Rock (hand placed): 1:1.5

    • Ordinary earth: 1:3

  • Schedule of Common Gradients:

    • Lawns, grassed areas: Maximum preferred 1:4 (25\%), minimum preferred 1:50 (2\%).

      • 1:4 is maximum for ride-on and gang-mowing.

      • Slopes covered only by shrubs will tend to erode over 1:10 (10\%).

    • Grassed playing fields: Maximum preferred 1:50 (2\%), minimum preferred 1:100 (1\%).

    • Berms and mounds: Maximum preferred 1:4 (25\%).

    • Mown slopes: Maximum preferred 1:4 (25\%).

    • Unmown grassed slopes: Maximum preferred 1:5 (20\%).

    • Planted slopes/beds: Minimum preferred 1:10 (10\%).

    • Preferred crown for unsealed roads: 1:20 (5\%).

    • Preferred crown for sealed roads: 1:33.3 (3\%).

    • Preferred maximum for driveways: 1:5 (20\%).

    • Preferred maximum for wheelchair use: 1:20 (5\%).

    • Preferred minimum for grassed areas: 1:50 (2\%).

    • Preferred minimum for paved areas: 1:100 (1\%).

  • Other Gradient Standards for Specific Use Types:

    • Public Streets: Extreme range 0.5-10\%, desirable range 1-8\%.

    • Private Roads: Extreme range 0.5-20\%, desirable range 1-12\%.

    • Service Drives: Extreme range 1-10\%, desirable range 1-5\%.

    • Parking Areas: Extreme range 0.5-15\%, desirable range 0.5-8\%.

      • Preferred gradient at loading/unloading areas is 1-3\%.

    • Parking Ramps: Extreme range up to 20\%, desirable range up to 12\%. (1:15 = 6.68\%).

    • Collector Walks: Extreme range 0.5-8\%, desirable range 0.5-3\%.

    • Entrance Walks: Extreme range up to 12\%, desirable range 1-8\%.

    • Pedestrian Ramps: Extreme range 25-50\%, desirable range 33-50\%. Slope reinforcement (bolster walls with steel grid elements, earth nailing, or reinforced earth) required for these steep slopes.

    • Stairs: Given angles of 90^ ext{o}, 70^ ext{o}. (Note: These likely refer to very steep slope conditions, not the tread gradient).

    • Game Courts: (No specific percentage range given, but playfields like football may be level longitudinally with a 2-3\% cross slope).

    • Play Fields: (See above).

    • Paved Gutters: Extreme range 0.25-100\%, desirable range 1-4\%.

    • Grassed Swales: Extreme range 0.5-15\%, desirable range up to 8\%. (Dependent on soil type).

    • Terrace and Sitting Areas: Extreme range up to 15\%, desirable range 0.5-3\%.

    • Grassed Banks: Extreme range up to 50\%.

      • Maximum slope recommended for power mower is 25\%.

      • 1:2 (50\%) is recommended maximum value for meadow slopes in parks.

      • 1:3 (33\%) is recommended maximum value for sloping lawns in parks.

      • 15\% allows unrestricted use of mowing machines.

    • Planted Banks: Extreme range up to 100\%.

      • Increased care and additional watering may be required for high maintenance areas.

      • Slope secured with geogrids for 1:1.5 (66\%, max value for unsecured slopes, regular for road/canal building, erosion protection mats recommended).

      • 1:1.25 (80\%) is the maximum natural slope angle (may be shallower according to soil type).

Slope Analysis

  • Purpose: Undertaken as part of the site analysis process to understand water behavior, landform, and other site aspects.

  • Application: Forms the crucial basis for land use planning, guiding the placement of activities and structures within the landscape based on their suitability for specific slopes. This often results in a "Sensitivity map" and a "Landscape Development Framework."

  • General Slope Classification:

    • Gentle Slope: 0 - 5\% (up to 1:20)

    • Moderate Slope: 6 - 15\% (1:20 to 1:7)

    • Steep Slope: 16 - 25\% (1:7 to 1:4)

    • Very Steep Slope: > 25\% (1:4 or more)

  • Gradient Formula Application: The gradient formula (G = D/L) is consistently used during slope analysis.

  • Outcome: A map that clearly indicates different areas segmented and colored according to their specific slope classifications.

Architectural and Landscape Examples

  • Various projects illustrate the application of grading and contour principles in practice:

    • Water Villas and floating structures.

    • Projects by architects such as Hiroyuki Arima, Waldemarson Berglund, Wespi De Meuron Romeo Architects, Denis Joelsons, Gabriela Baraúna Uchida.

    • Candlestick Park by George Hargreaves.

    • Alvar Aalto Studio.

    • Kimmel residence by Dan Kiley.

    • Hollyhock House and Olive Hill (Frank Lloyd Wright).

    • Boarding School Mare de Déu de la Vallivana by Carme Pinós and Enric Miralles.

    • Tippet Rise Art Center pavilion by Francis Kéré.

    • Korman House by Louis Kahn.

Site Design Elements and Data

  • Detailed site plans often include:

    • Electrical and telephone lines.

    • Storm drains.

    • Roads (e.g., East Broadacres Road).

    • Tennis courts.

    • Building floor levels (e.g., First Floor Elev. 270.5).

    • Pools with specific rim elevations (e.g., Rim of Pool EL 253.0).

    • Landscape features like lawns, fire pits, planting beds, hedges, trellises, brick walks, and seating walls.

    • Top of curb/bottom of curb, top of wall/bottom of wall, finished floor level notations.

    • Numerical coordinate references (N, E) for specific points or changes in design.