Runoff Coefficient Table
Area Description Runoff Coefficient C
Business
Downtown 0.70-0.95
Neighborhood 0.50-0.70
Residential
Single-Family 0.30-0.50
Multiunits, detached 0.40-0.60
Multiunits, attached 0.60-0.75
Residential (suburban) 0.25-0.40
Apartment 0.50-0.70
Industrial
Light 0.50-0.80
Heavy 0.60-0.90
Parks, cemeteries 0.10-0.25
Playgrounds 0.20-0.35
Railroad yard 0.20-0.35
Unimproved 0.10-0.30
Pavement
Asphaltic and concrete 0.70-0.95
Brick 0.70-0.85
Roofs 0.75-0.95
Lawns, sandy soil
Flat, 2 percent 0.05-0.10
Average, 2-7 percent 0.10-0.15
Steep, 7 percent 0.15-0.20
Lawns, heavy soil
Flat, 2 percent 0.13-0.17
Average, 2-7 percent 0.18-0.22
Steep, 7 percent 0.25-0.35
http://www.ems-i.com/wmshelp/Hydrologic_Models/Models/Rational/Equation/Runoff_Coefficient_Table.htm
Thursday, July 19, 2007
Wednesday, July 18, 2007
TMDL and NPDEs
TMDL is a calculation of maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and an allocation of that amount ...
Monday, July 2, 2007
Hydraulic Head, Salt water related hydraulic head measures
Quote of the day: 学朋友长处，行圣贤语言
Hydraulic head, Fresh water head, Environmental head, Saltwater head, pressure head
Hydraulic head (total head) = pressure head + elevation head = constant for a static water column.
Equivalent Fresh water head in saltwater problems is similar to hydraulic head. It determines the flow of water.
Environmental head (Modflow-surface, HGL): computed from the equivalent freshwater head at any location, by subtracting the effects of density from that point up to the surface. Note that this an integrated process, concentration may varying from that point up to the surface. In the real world, this can be water level measured from an open hole well (opens from the point to the surface)
Saltwater head, native head (SEAWAT, USGS): computed from the equivalent freshwater head at any location, by subtracting the effects of density from that point only. Note that this is not an integrated process, concentration is a point value. In the real world, this can be water level measured from an well with a short screen opening.
Previous version of SEAWAT, input and output were expressed in terms of equivalent freshwater head.
SEAWAT-2000 uses equivalent freshwater head as the dependent variable in thevariable-density ground-water flow equation. But input and output are expressed in terms of the head of the native aquifer water (saltwater head)
So, for a given point, usually Equvalent Fresh water head >= Saltwater Head, native head (SEAWAT) >= Environmental Head (Modflow-surfact)
Hydraulic head, Fresh water head, Environmental head, Saltwater head, pressure head
Hydraulic head (total head) = pressure head + elevation head = constant for a static water column.
Equivalent Fresh water head in saltwater problems is similar to hydraulic head. It determines the flow of water.
Environmental head (Modflow-surface, HGL): computed from the equivalent freshwater head at any location, by subtracting the effects of density from that point up to the surface. Note that this an integrated process, concentration may varying from that point up to the surface. In the real world, this can be water level measured from an open hole well (opens from the point to the surface)
Saltwater head, native head (SEAWAT, USGS): computed from the equivalent freshwater head at any location, by subtracting the effects of density from that point only. Note that this is not an integrated process, concentration is a point value. In the real world, this can be water level measured from an well with a short screen opening.
Previous version of SEAWAT, input and output were expressed in terms of equivalent freshwater head.
SEAWAT-2000 uses equivalent freshwater head as the dependent variable in thevariable-density ground-water flow equation. But input and output are expressed in terms of the head of the native aquifer water (saltwater head)
So, for a given point, usually Equvalent Fresh water head >= Saltwater Head, native head (SEAWAT) >= Environmental Head (Modflow-surfact)
Modflow Sf1, sf2, ss and porosity
Quote of the Day: 教于幼正大光明，检于心忧勤惕厉
Please correct me if I am wrong...
My notes: Modflow Sf1, sf2, ss and porosity
Sf1: the primary storage coefficient, the storability. Read only for a transient
simulation (steady-state flag, ISS, is 0). SF1 would normally be confined storage coefficient.
The primary storage coefficient divided by the block thickness is equal to the specific storage Ss.
Usually in the range of 1e-3 to 1e-6. Represent the spongy characteristics of a confined aquifer.
Sf2: secondary storage coefficient, the specific yield. SF2 is read only if
the simulation is transient (steady-state flag, ISS, is 0). SF2 is approx. to porosity for a unconfined layer, but is smaller than porosity for a confined aquifer or an aquifer under pressure. sf2 is used to simulate water table in an aquifer.
sf2 is usually in the range of 0.1~0.4.
Ss: Specific storage
Sf1: storativity = Ss*b (depth of a confined layer)
Sf2: Specific yield
Wikepedia
Specific storage and specific yield
Main article: Specific storage
Specific storage (Ss) and its depth-integrated equivalent, storativity (S=Ss*b), are indirect aquifer properties (they cannot be measured directly); they indicate the amount of groundwater released from storage due to a unit depressurization of a confined aquifer. They are fractions between 0 and 1.
Specific yield (Sy) is also a ratio between 0 and 1 (Sy ≤ porosity) which indicates the amount of water released due to drainage, from lowering the water table in an unconfined aquifer. Typically Sy is orders of magnitude larger than Ss. Often the porosity or effective porosity is used as an upper bound to the specific yield.
Specific storage is typically very small, generally 0.0001 1/ft or less
Storativity is a dimensionless quantity, and ranges between 0 and the effective porosity of the aquifer; although for confined aquifers, this number is usually much less than 0.01
Specific yield, also known as the drainable porosity, is a ratio, less than or equal to the effective porosity, indicating the volumetric fraction of the bulk aquifer volume that a given aquifer will yield when all the water is allowed to drain out of it under the forces of gravity
Typical Specific yield values: (low mid high)
Unconsolidated deposits
Clay: 0 2 5
Sandy clay (mud): 3 7 12
Silt: 3 18 19
Fine sand: 10 21 28
Medium sand: 15 26 32
Coarse sand: 20 27 35
Gravelly sand: 20 25 35
Fine gravel: 21 25 35
Medium gravel: 13 23 26
Coarse gravel: 12 22 26
Consolidated deposits
Fine-grained sandstone: 21
Medium-grained sandstone: 27
Limestone: 14
Schist: 26
Siltstone: 12
Tuff: 21
Other deposits: Dune sand 38
Loess : 18
Peat: 44
Till, predominantly silt: 6
Till, predominantly sand: 16
Till, predominantly gravel: 16
Please correct me if I am wrong...
My notes: Modflow Sf1, sf2, ss and porosity
Sf1: the primary storage coefficient, the storability. Read only for a transient
simulation (steady-state flag, ISS, is 0). SF1 would normally be confined storage coefficient.
The primary storage coefficient divided by the block thickness is equal to the specific storage Ss.
Usually in the range of 1e-3 to 1e-6. Represent the spongy characteristics of a confined aquifer.
Sf2: secondary storage coefficient, the specific yield. SF2 is read only if
the simulation is transient (steady-state flag, ISS, is 0). SF2 is approx. to porosity for a unconfined layer, but is smaller than porosity for a confined aquifer or an aquifer under pressure. sf2 is used to simulate water table in an aquifer.
sf2 is usually in the range of 0.1~0.4.
Ss: Specific storage
Sf1: storativity = Ss*b (depth of a confined layer)
Sf2: Specific yield
Wikepedia
Specific storage and specific yield
Main article: Specific storage
Specific storage (Ss) and its depth-integrated equivalent, storativity (S=Ss*b), are indirect aquifer properties (they cannot be measured directly); they indicate the amount of groundwater released from storage due to a unit depressurization of a confined aquifer. They are fractions between 0 and 1.
Specific yield (Sy) is also a ratio between 0 and 1 (Sy ≤ porosity) which indicates the amount of water released due to drainage, from lowering the water table in an unconfined aquifer. Typically Sy is orders of magnitude larger than Ss. Often the porosity or effective porosity is used as an upper bound to the specific yield.
Specific storage is typically very small, generally 0.0001 1/ft or less
Storativity is a dimensionless quantity, and ranges between 0 and the effective porosity of the aquifer; although for confined aquifers, this number is usually much less than 0.01
Specific yield, also known as the drainable porosity, is a ratio, less than or equal to the effective porosity, indicating the volumetric fraction of the bulk aquifer volume that a given aquifer will yield when all the water is allowed to drain out of it under the forces of gravity
Typical Specific yield values: (low mid high)
Unconsolidated deposits
Clay: 0 2 5
Sandy clay (mud): 3 7 12
Silt: 3 18 19
Fine sand: 10 21 28
Medium sand: 15 26 32
Coarse sand: 20 27 35
Gravelly sand: 20 25 35
Fine gravel: 21 25 35
Medium gravel: 13 23 26
Coarse gravel: 12 22 26
Consolidated deposits
Fine-grained sandstone: 21
Medium-grained sandstone: 27
Limestone: 14
Schist: 26
Siltstone: 12
Tuff: 21
Other deposits: Dune sand 38
Loess : 18
Peat: 44
Till, predominantly silt: 6
Till, predominantly sand: 16
Till, predominantly gravel: 16
Sunday, July 1, 2007
Brackish water
Water salinity based on dissolved salts in percent (%)
Fresh water:< 0.05 % (<500 ppm)
Brackish water:0.05 - 3 % (500~3000pm)
Saline water:3 - 5 % (3000~5000ppm)
Brine:> 5 %
http://en.wikipedia.org/wiki/Brackish_water
地下水中分布最广的是钾、钠、镁、钙、氯、硫酸根和碳酸氢根 7 种离子。地下水中各种离子、分子和化合物的总量称总矿化度 ，总矿化度小于1克／升的 ，称淡水，1～3克／升的 ，称微水，3 ～ 10克／升的，称咸水 ，10～50克／升的，称盐水，大于 50 克／升的，称卤水。地下水中钙、镁、铁、锰、锶、铝等溶解盐类的含量称硬度，含量高的硬度大，反之硬度小。
地下水是指埋藏在地面以下，存在于岩石和土壤的孔隙中可以流动的水体。地面以下的水并不都是地下水。地面以下的土层可分为包气带、饱水带。包气带的土层中含有空气，没有被水充满，包气带中的水分称为土壤水。饱水带中土壤孔隙被水充满，含水量达到饱和，饱水带中的水即为地下水。常见的井水、泉水都是地下水。地下水分布广泛，水量也较稳定，是工农业和生活用水的重要水源之一。地下水的过量开采（开采速度大于其补给速度）会造成地下水位的大幅下降，引起地面沉降。地下水位过高会对农作物生长不利，会造成渍害，若地下水含盐量较高，则会产生土地的次生盐碱化。 地下水污染 与地表水一样，地下水也受到了污染的威胁，主要来自于地表或土壤水的下渗，农用氮肥以及垃圾中的油、酚污染着地下水，氮肥中的硝酸盐一旦进入地下，便转变为亚硝酸盐，它在人体中能够转变成致癌物质。地面植被的破坏和湿地的排水减少了地表水的渗透，从而降低了潜水面。由于城市和工业的过度需要，淡水不断被抽出作为生活和工业用水，然后作为地表污水重新排放，因而还会导致潜水面的进一步下降。另一方面，大量频繁的灌溉可以增强渗透作用，使潜水面一直升到地表。而在干旱地区，被水渗透的土地由于异常的蒸发作用，引起地下水中盐类的沉淀，迟早会变成不能耕作的盐碱地。
地下水广泛埋藏于地表以下的各种状态的水，统称为地下水。大气降水是地下水的主要来源。根据地下埋藏条件的不同，地下水可分为上层滞水、潜水和自流水三大类。 上层滞水是由于局部的隔水作用，使下渗的大气降水停留在浅层的岩石裂缝或沉积层中所形成的蓄水体。潜水是埋藏于地表以下第一个稳定隔水层上的地下水，通常所见到的地下水多半是潜水。当潜水流出地面时就形成泉。自流水是埋藏较深的、流动于两个隔水层之间的地下水。这种地下水往往具有较大的水压力，特别是当上下两个隔水层呈倾斜状时，隔层中的水体要承受更大的水压力。当井或钻孔穿过上层顶板时，强大的压力就会使水体喷涌而出，形成自流水。
根据埋藏条件可把地下水分为包气带水、潜水和承压水。包气带水指潜水面以上包气带中的水，这里有吸着水、薄膜水、毛管水、气态水和暂时存在的重力水。包气带中局部隔水层之上季节性地存在的水称上层滞水。潜水是指存在于地表以下第一个稳定隔水层上面、具有自由水面的重力水。它主要由降水和地表水入渗补给。承压水是充满于上下两个隔水层之间的含水层中的水。它承受压力，当上覆的隔水层被凿穿时，水能从钻孔上升或喷出。按含水空隙的类型，地下水又被分为孔隙水、裂隙水和岩溶水。孔隙水是存在于岩土孔隙中的地下水，如松散的砂层、砾石层和砂岩层中的地下水。裂隙水是存在于坚硬岩石和某些粘土层裂隙中的水。岩溶水又称喀斯特水，指存在于可溶岩石（如石灰岩、白云岩等）的洞隙中的地下水。
Fresh water:< 0.05 % (<500 ppm)
Brackish water:0.05 - 3 % (500~3000pm)
Saline water:3 - 5 % (3000~5000ppm)
Brine:> 5 %
http://en.wikipedia.org/wiki/Brackish_water
地下水中分布最广的是钾、钠、镁、钙、氯、硫酸根和碳酸氢根 7 种离子。地下水中各种离子、分子和化合物的总量称总矿化度 ，总矿化度小于1克／升的 ，称淡水，1～3克／升的 ，称微水，3 ～ 10克／升的，称咸水 ，10～50克／升的，称盐水，大于 50 克／升的，称卤水。地下水中钙、镁、铁、锰、锶、铝等溶解盐类的含量称硬度，含量高的硬度大，反之硬度小。
地下水是指埋藏在地面以下，存在于岩石和土壤的孔隙中可以流动的水体。地面以下的水并不都是地下水。地面以下的土层可分为包气带、饱水带。包气带的土层中含有空气，没有被水充满，包气带中的水分称为土壤水。饱水带中土壤孔隙被水充满，含水量达到饱和，饱水带中的水即为地下水。常见的井水、泉水都是地下水。地下水分布广泛，水量也较稳定，是工农业和生活用水的重要水源之一。地下水的过量开采（开采速度大于其补给速度）会造成地下水位的大幅下降，引起地面沉降。地下水位过高会对农作物生长不利，会造成渍害，若地下水含盐量较高，则会产生土地的次生盐碱化。 地下水污染 与地表水一样，地下水也受到了污染的威胁，主要来自于地表或土壤水的下渗，农用氮肥以及垃圾中的油、酚污染着地下水，氮肥中的硝酸盐一旦进入地下，便转变为亚硝酸盐，它在人体中能够转变成致癌物质。地面植被的破坏和湿地的排水减少了地表水的渗透，从而降低了潜水面。由于城市和工业的过度需要，淡水不断被抽出作为生活和工业用水，然后作为地表污水重新排放，因而还会导致潜水面的进一步下降。另一方面，大量频繁的灌溉可以增强渗透作用，使潜水面一直升到地表。而在干旱地区，被水渗透的土地由于异常的蒸发作用，引起地下水中盐类的沉淀，迟早会变成不能耕作的盐碱地。
地下水广泛埋藏于地表以下的各种状态的水，统称为地下水。大气降水是地下水的主要来源。根据地下埋藏条件的不同，地下水可分为上层滞水、潜水和自流水三大类。 上层滞水是由于局部的隔水作用，使下渗的大气降水停留在浅层的岩石裂缝或沉积层中所形成的蓄水体。潜水是埋藏于地表以下第一个稳定隔水层上的地下水，通常所见到的地下水多半是潜水。当潜水流出地面时就形成泉。自流水是埋藏较深的、流动于两个隔水层之间的地下水。这种地下水往往具有较大的水压力，特别是当上下两个隔水层呈倾斜状时，隔层中的水体要承受更大的水压力。当井或钻孔穿过上层顶板时，强大的压力就会使水体喷涌而出，形成自流水。
根据埋藏条件可把地下水分为包气带水、潜水和承压水。包气带水指潜水面以上包气带中的水，这里有吸着水、薄膜水、毛管水、气态水和暂时存在的重力水。包气带中局部隔水层之上季节性地存在的水称上层滞水。潜水是指存在于地表以下第一个稳定隔水层上面、具有自由水面的重力水。它主要由降水和地表水入渗补给。承压水是充满于上下两个隔水层之间的含水层中的水。它承受压力，当上覆的隔水层被凿穿时，水能从钻孔上升或喷出。按含水空隙的类型，地下水又被分为孔隙水、裂隙水和岩溶水。孔隙水是存在于岩土孔隙中的地下水，如松散的砂层、砾石层和砂岩层中的地下水。裂隙水是存在于坚硬岩石和某些粘土层裂隙中的水。岩溶水又称喀斯特水，指存在于可溶岩石（如石灰岩、白云岩等）的洞隙中的地下水。
Range of Hydraulic Conductivity
水利传导系数只跟土壤情况有关。
但是楼主问的是流速，所以应该考虑水利坡度，dh/dl。。达西定律
一般的水利传导系数：
1e-2~1e-1(cm/s),非常好的蓄水层，沙，碎石
1e-2~1e-6(cm/s),差的蓄水层，细沙，泥沙，土
1e-6~1e-10,基本不透水层，粘土，有机粘土
(Jacob Bear) http://en.wikipedia.org/wiki/Hydraulic_conductivity#Ranges_of_values_for_natural_materials
但是楼主问的是流速，所以应该考虑水利坡度，dh/dl。。达西定律
一般的水利传导系数：
1e-2~1e-1(cm/s),非常好的蓄水层，沙，碎石
1e-2~1e-6(cm/s),差的蓄水层，细沙，泥沙，土
1e-6~1e-10,基本不透水层，粘土，有机粘土
(Jacob Bear) http://en.wikipedia.org/wiki/Hydraulic_conductivity#Ranges_of_values_for_natural_materials
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